CBSE 10th Physics Full Notes + PYQ's.pdf
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About This Presentation
CBSE 10th Physics Full Notes + PYQ's
Slide Content
PHYSICS
CBSE Class
10th
Karanjot SIngh
written by
CBSE Class
10th
Karanjot SIngh
written by
CBSE Class 10 Science: Natural
Phenomena
Part 1: Detailed Notes
Reflection of Light by Curved Surfaces
Spherical mirrors are reflective surfaces that form part of a hollow sphere. These mirrors
can be broadly categorized into two types, distinguished by their reflecting surfaces:
● Concave Mirror: This mirror possesses a reflecting surface that is curved inwards,
resembling the inside of a spoon. When a beam of parallel light rays strikes a concave
mirror, it is converged to a single point known as the principal focus. This converging
property makes concave mirrors highly useful in applications such as shaving mirrors,
where they produce an enlarged, erect image of the face, and in car headlights, where
they are used to reflect light from a bulb into a powerful, parallel beam.
● Convex Mirror: In contrast, a convex mirror has a reflecting surface that bulges
outwards. This configuration causes an incident beam of parallel light rays to diverge
after reflection, as if originating from a single point behind the mirror (the principal
focus). Due to their ability to provide a wide field of view, convex mirrors are commonly
employed as rearview mirrors in vehicles and as security mirrors in retail stores.
Key Terms for Spherical Mirrors
The behavior of spherical mirrors is described by a set of fundamental terms:
● Centre of Curvature (C): This is the geometric center of the hollow sphere from which
the mirror is a part.
● Principal Axis: An imaginary straight line that passes through the pole (P) and the
centre of curvature (C) of a spherical mirror. This axis serves as a key reference for ray
diagrams and calculations.
● Pole (P): The central point of the reflecting surface of a spherical mirror.
● Aperture: The diameter of the reflecting surface, which determines the amount of light
the mirror can capture.
● Principal Focus (F): For a concave mirror, this is the point on the principal axis where
light rays parallel to the axis converge after reflection. For a convex mirror, it is the point
from which parallel rays appear to diverge after reflection.
● Focal Length (f): The linear distance between the pole (P) and the principal focus (F).
The focal length is always half the radius of curvature (R), a relationship expressed as
f=2R.
Mirror Formula and Magnification
Phenomena
Part 1: Detailed Notes
Reflection of Light by Curved Surfaces
Spherical mirrors are reflective surfaces that form part of a hollow sphere. These mirrors
can be broadly categorized into two types, distinguished by their reflecting surfaces:
● Concave Mirror: This mirror possesses a reflecting surface that is curved inwards,
resembling the inside of a spoon. When a beam of parallel light rays strikes a concave
mirror, it is converged to a single point known as the principal focus. This converging
property makes concave mirrors highly useful in applications such as shaving mirrors,
where they produce an enlarged, erect image of the face, and in car headlights, where
they are used to reflect light from a bulb into a powerful, parallel beam.
● Convex Mirror: In contrast, a convex mirror has a reflecting surface that bulges
outwards. This configuration causes an incident beam of parallel light rays to diverge
after reflection, as if originating from a single point behind the mirror (the principal
focus). Due to their ability to provide a wide field of view, convex mirrors are commonly
employed as rearview mirrors in vehicles and as security mirrors in retail stores.
Key Terms for Spherical Mirrors
The behavior of spherical mirrors is described by a set of fundamental terms:
● Centre of Curvature (C): This is the geometric center of the hollow sphere from which
the mirror is a part.
● Principal Axis: An imaginary straight line that passes through the pole (P) and the
centre of curvature (C) of a spherical mirror. This axis serves as a key reference for ray
diagrams and calculations.
● Pole (P): The central point of the reflecting surface of a spherical mirror.
● Aperture: The diameter of the reflecting surface, which determines the amount of light
the mirror can capture.
● Principal Focus (F): For a concave mirror, this is the point on the principal axis where
light rays parallel to the axis converge after reflection. For a convex mirror, it is the point
from which parallel rays appear to diverge after reflection.
● Focal Length (f): The linear distance between the pole (P) and the principal focus (F).
The focal length is always half the radius of curvature (R), a relationship expressed as
f=2R.
Mirror Formula and Magnification
The Mirror Formula is a mathematical relationship that connects the object distance (u),
image distance (v), and focal length (f) of a spherical mirror. The formula is given by:
v1+u1=f1
The sign conventions for these variables are crucial for accurate calculations. A negative
object distance (u) indicates that the object is placed in front of the mirror, while a negative
image distance (v) signifies a virtual image formed behind the mirror.
● Magnification (m): Magnification is a dimensionless quantity that describes the relative
size and orientation of an image. It is defined as the ratio of the height of the image (h′)
to the height of the object (h). It can also be calculated as the negative ratio of the
image distance to the object distance:
m=hh′=−uv
A value of m greater than 1 implies that the image is magnified, whereas a value less than 1
indicates a diminished image. A negative sign for m signifies that the image is real and
inverted, while a positive sign indicates a virtual and erect image.
Image Formation by Spherical Mirrors
Table: Image Formation by Concave Mirror
Position of the
Object
Position of the
Image
Size of the Image Nature of the
Image
At infinity At the principal
focus (F)
Highly diminished,
point-sized
Real and inverted
Beyond the centre
of curvature (C)
Between F and C Diminished Real and inverted
At the centre of
curvature (C)
At the centre of
curvature (C)
Same size Real and inverted
Between C and F Beyond C Enlarged Real and inverted
At the principal
focus (F)
At infinity Highly enlarged Real and inverted
Between the pole
(P) and F
Behind the mirror Enlarged Virtual and erect
image distance (v), and focal length (f) of a spherical mirror. The formula is given by:
v1+u1=f1
The sign conventions for these variables are crucial for accurate calculations. A negative
object distance (u) indicates that the object is placed in front of the mirror, while a negative
image distance (v) signifies a virtual image formed behind the mirror.
● Magnification (m): Magnification is a dimensionless quantity that describes the relative
size and orientation of an image. It is defined as the ratio of the height of the image (h′)
to the height of the object (h). It can also be calculated as the negative ratio of the
image distance to the object distance:
m=hh′=−uv
A value of m greater than 1 implies that the image is magnified, whereas a value less than 1
indicates a diminished image. A negative sign for m signifies that the image is real and
inverted, while a positive sign indicates a virtual and erect image.
Image Formation by Spherical Mirrors
Table: Image Formation by Concave Mirror
Position of the
Object
Position of the
Image
Size of the Image Nature of the
Image
At infinity At the principal
focus (F)
Highly diminished,
point-sized
Real and inverted
Beyond the centre
of curvature (C)
Between F and C Diminished Real and inverted
At the centre of
curvature (C)
At the centre of
curvature (C)
Same size Real and inverted
Between C and F Beyond C Enlarged Real and inverted
At the principal
focus (F)
At infinity Highly enlarged Real and inverted
Between the pole
(P) and F
Behind the mirror Enlarged Virtual and erect
Table: Image Formation by Convex Mirror
Position of the
Object
Position of the
Image
Size of the Image Nature of the
Image
At infinity At the principal
focus (F), behind
the mirror
Highly diminished,
point-sized
Virtual and erect
Between infinity
and the pole (P)
Between P and F,
behind the mirror
Diminished Virtual and erect
Refraction of Light
Refraction is the phenomenon of light bending as it passes from one transparent medium to
another. This change in direction occurs because the speed of light varies in different media.
The degree of bending depends on the properties of the two media and the angle at which
the light ray enters the new medium.
Laws of Refraction:
1. The incident ray, the refracted ray, and the normal to the interface at the point of
incidence all lie within the same plane.
2. Snell's Law: This law provides a quantitative relationship between the angles of
incidence and refraction. It states that the ratio of the sine of the angle of incidence
(sini) to the sine of the angle of refraction (sinr) is a constant for a given pair of
media.sinrsini=constant
Refractive Index (n): The refractive index of a medium is a measure of how much the speed
of light is reduced in that medium compared to a vacuum. It is defined as the ratio of the
speed of light in a vacuum to the speed of light in the medium.
n=Speed of light in mediumSpeed of light in vacuum
A higher refractive index indicates an optically denser medium, where light travels at a slower
speed.
Refraction by Spherical Lenses
Spherical lenses are made of transparent material with one or two spherical surfaces. They
are a fundamental component of many optical instruments.
● Convex Lens (Converging Lens): A convex lens is thicker at its center than at its
edges. It converges parallel light rays to a single point after refraction. Its applications
Position of the
Object
Position of the
Image
Size of the Image Nature of the
Image
At infinity At the principal
focus (F), behind
the mirror
Highly diminished,
point-sized
Virtual and erect
Between infinity
and the pole (P)
Between P and F,
behind the mirror
Diminished Virtual and erect
Refraction of Light
Refraction is the phenomenon of light bending as it passes from one transparent medium to
another. This change in direction occurs because the speed of light varies in different media.
The degree of bending depends on the properties of the two media and the angle at which
the light ray enters the new medium.
Laws of Refraction:
1. The incident ray, the refracted ray, and the normal to the interface at the point of
incidence all lie within the same plane.
2. Snell's Law: This law provides a quantitative relationship between the angles of
incidence and refraction. It states that the ratio of the sine of the angle of incidence
(sini) to the sine of the angle of refraction (sinr) is a constant for a given pair of
media.sinrsini=constant
Refractive Index (n): The refractive index of a medium is a measure of how much the speed
of light is reduced in that medium compared to a vacuum. It is defined as the ratio of the
speed of light in a vacuum to the speed of light in the medium.
n=Speed of light in mediumSpeed of light in vacuum
A higher refractive index indicates an optically denser medium, where light travels at a slower
speed.
Refraction by Spherical Lenses
Spherical lenses are made of transparent material with one or two spherical surfaces. They
are a fundamental component of many optical instruments.
● Convex Lens (Converging Lens): A convex lens is thicker at its center than at its
edges. It converges parallel light rays to a single point after refraction. Its applications
include magnifying glasses, cameras, and microscopes.
● Concave Lens (Diverging Lens): A concave lens is thinner at its center than at its
edges. It causes parallel light rays to diverge after passing through it, as if originating
from a single point. It is used to correct certain vision defects and in peep holes.
Lens Formula and Magnification
The Lens Formula is analogous to the mirror formula and relates the object distance (u),
image distance (v), and focal length (f) of a spherical lens.
v1−u1=f1
Power of a Lens (P): The power of a lens is a measure of its ability to converge or diverge
light. It is defined as the reciprocal of its focal length expressed in metres.
P=f(in metres)1
The SI unit for power is the dioptre (D). A convex lens has positive power, while a concave
lens has negative power. For example, a convex lens with a focal length of 0.5m has a power
of 2D.
Image Formation by Spherical Lenses
Table: Image Formation by Convex Lens
Position of the
Object
Position of the
Image
Size of the Image Nature of the
Image
At infinity At the principal
focus (F2)
Highly diminished,
point-sized
Real and inverted
Beyond 2F1 Between F2 and
2F2
Diminished Real and inverted
At 2F1 At 2F2 Same size Real and inverted
Between F1 and 2F1 Beyond 2F2 Enlarged Real and inverted
At the principal
focus (F1)
At infinity Highly enlarged Real and inverted
Between the
optical centre (O)
and F1
On the same side
as the object
Enlarged Virtual and erect
● Concave Lens (Diverging Lens): A concave lens is thinner at its center than at its
edges. It causes parallel light rays to diverge after passing through it, as if originating
from a single point. It is used to correct certain vision defects and in peep holes.
Lens Formula and Magnification
The Lens Formula is analogous to the mirror formula and relates the object distance (u),
image distance (v), and focal length (f) of a spherical lens.
v1−u1=f1
Power of a Lens (P): The power of a lens is a measure of its ability to converge or diverge
light. It is defined as the reciprocal of its focal length expressed in metres.
P=f(in metres)1
The SI unit for power is the dioptre (D). A convex lens has positive power, while a concave
lens has negative power. For example, a convex lens with a focal length of 0.5m has a power
of 2D.
Image Formation by Spherical Lenses
Table: Image Formation by Convex Lens
Position of the
Object
Position of the
Image
Size of the Image Nature of the
Image
At infinity At the principal
focus (F2)
Highly diminished,
point-sized
Real and inverted
Beyond 2F1 Between F2 and
2F2
Diminished Real and inverted
At 2F1 At 2F2 Same size Real and inverted
Between F1 and 2F1 Beyond 2F2 Enlarged Real and inverted
At the principal
focus (F1)
At infinity Highly enlarged Real and inverted
Between the
optical centre (O)
and F1
On the same side
as the object
Enlarged Virtual and erect
Table: Image Formation by Concave Lens
Position of the
Object
Position of the
Image
Size of the Image Nature of the
Image
At infinity At the principal
focus (F1)
Highly diminished,
point-sized
Virtual and erect
Between infinity
and the optical
centre (O)
Between F1 and O Diminished Virtual and erect
The Human Eye and Vision Defects
The human eye is a complex optical system that functions like a camera. The cornea, iris, and
crystalline lens collectively focus light onto the light-sensitive retina. The ability of the eye to
adjust the focal length of its lens to focus on objects at different distances is called
accommodation. This is achieved by the action of the ciliary muscles, which change the
curvature of the eye lens.
Defects of Vision:
1. Myopia (Nearsightedness): This defect occurs when a person can see nearby objects
clearly but cannot see distant objects distinctly. It arises either because the eyeball is
too long or the eye lens has excessive converging power. As a result, the image of a
distant object is formed in front of the retina. Myopia is corrected by using a concave
lens of suitable power, which diverges the light rays to ensure the image is formed
directly on the retina.
2. Hypermetropia (Farsightedness): This is a condition where a person can see distant
objects clearly but has difficulty viewing nearby objects. The defect is caused by the
eyeball being too short or the eye lens having insufficient converging power. The image
of a nearby object is therefore formed behind the retina. Hypermetropia is corrected by
using a convex lens of appropriate power to converge the light rays to form the image
on the retina.
Refraction of Light Through a Prism and Scattering
A prism is a transparent medium with at least two non-parallel plane surfaces. When light
passes through a prism, it undergoes refraction at each surface. The deviation of the light ray
from its original path is known as the angle of deviation.
Dispersion of Light: The phenomenon of a beam of white light splitting into its seven
Position of the
Object
Position of the
Image
Size of the Image Nature of the
Image
At infinity At the principal
focus (F1)
Highly diminished,
point-sized
Virtual and erect
Between infinity
and the optical
centre (O)
Between F1 and O Diminished Virtual and erect
The Human Eye and Vision Defects
The human eye is a complex optical system that functions like a camera. The cornea, iris, and
crystalline lens collectively focus light onto the light-sensitive retina. The ability of the eye to
adjust the focal length of its lens to focus on objects at different distances is called
accommodation. This is achieved by the action of the ciliary muscles, which change the
curvature of the eye lens.
Defects of Vision:
1. Myopia (Nearsightedness): This defect occurs when a person can see nearby objects
clearly but cannot see distant objects distinctly. It arises either because the eyeball is
too long or the eye lens has excessive converging power. As a result, the image of a
distant object is formed in front of the retina. Myopia is corrected by using a concave
lens of suitable power, which diverges the light rays to ensure the image is formed
directly on the retina.
2. Hypermetropia (Farsightedness): This is a condition where a person can see distant
objects clearly but has difficulty viewing nearby objects. The defect is caused by the
eyeball being too short or the eye lens having insufficient converging power. The image
of a nearby object is therefore formed behind the retina. Hypermetropia is corrected by
using a convex lens of appropriate power to converge the light rays to form the image
on the retina.
Refraction of Light Through a Prism and Scattering
A prism is a transparent medium with at least two non-parallel plane surfaces. When light
passes through a prism, it undergoes refraction at each surface. The deviation of the light ray
from its original path is known as the angle of deviation.
Dispersion of Light: The phenomenon of a beam of white light splitting into its seven
constituent colours (VIBGYOR) upon passing through a prism is called dispersion. This occurs
because the refractive index of the prism material is slightly different for each color, causing
each color to bend at a different angle. This results in the formation of a spectrum of colors.
Scattering of Light: The redirection of light rays by minute particles in the atmosphere is
known as the scattering of light. The extent of scattering is dependent on the wavelength of
light and the size of the scattering particles.
● The shorter wavelengths of light, such as blue and violet, are scattered more effectively
by the fine air molecules in the atmosphere than the longer wavelengths, such as red.
This is the primary reason why the sky appears blue on a clear day.
Part 2: Previous Year's Questions (PYQs)
Q1. The refractive index of diamond is 2.42. What is the meaning of this statement? (CBSE
2018)
A. The statement means that the speed of light in a vacuum is 2.42 times the speed of light in
diamond. A higher refractive index indicates that the medium is optically denser and the
speed of light is slower in it.
Q2. An object is placed at a distance of 10cm from a convex mirror of focal length 15cm. Find
the position and nature of the image. (CBSE 2016)
A.
Given:
Object distance, u=−10cm
Focal length, f=+15cm (for a convex mirror)
Using the mirror formula, v1+u1=f1
v1=f1−u1=151−−101=151+101
v1=302+3=305=61
v=+6cm
The image is formed at a distance of 6cm behind the mirror.
Nature of the image: The image is virtual, erect, and diminished.
Q3. An object placed in front of a concave mirror forms an image at the same position as the
object. What is the position of the object? (CBSE 2017)
A. The image formed by a concave mirror is at the same position and size as the object only
when the object is placed at the centre of curvature (C). The image formed is real and
inverted.
Q4. A student sitting in the last row of the classroom cannot read the writing on the
blackboard clearly but can read the book in his hands. Name the defect of vision he is
suffering from and how can it be corrected? (CBSE 2019)
because the refractive index of the prism material is slightly different for each color, causing
each color to bend at a different angle. This results in the formation of a spectrum of colors.
Scattering of Light: The redirection of light rays by minute particles in the atmosphere is
known as the scattering of light. The extent of scattering is dependent on the wavelength of
light and the size of the scattering particles.
● The shorter wavelengths of light, such as blue and violet, are scattered more effectively
by the fine air molecules in the atmosphere than the longer wavelengths, such as red.
This is the primary reason why the sky appears blue on a clear day.
Part 2: Previous Year's Questions (PYQs)
Q1. The refractive index of diamond is 2.42. What is the meaning of this statement? (CBSE
2018)
A. The statement means that the speed of light in a vacuum is 2.42 times the speed of light in
diamond. A higher refractive index indicates that the medium is optically denser and the
speed of light is slower in it.
Q2. An object is placed at a distance of 10cm from a convex mirror of focal length 15cm. Find
the position and nature of the image. (CBSE 2016)
A.
Given:
Object distance, u=−10cm
Focal length, f=+15cm (for a convex mirror)
Using the mirror formula, v1+u1=f1
v1=f1−u1=151−−101=151+101
v1=302+3=305=61
v=+6cm
The image is formed at a distance of 6cm behind the mirror.
Nature of the image: The image is virtual, erect, and diminished.
Q3. An object placed in front of a concave mirror forms an image at the same position as the
object. What is the position of the object? (CBSE 2017)
A. The image formed by a concave mirror is at the same position and size as the object only
when the object is placed at the centre of curvature (C). The image formed is real and
inverted.
Q4. A student sitting in the last row of the classroom cannot read the writing on the
blackboard clearly but can read the book in his hands. Name the defect of vision he is
suffering from and how can it be corrected? (CBSE 2019)
A. The student is suffering from Myopia (Nearsightedness). This is because he can see nearby
objects (the book) clearly but not distant objects (the blackboard). It can be corrected by
using a concave lens of appropriate power. The concave lens diverges the light rays slightly
before they enter the eye, allowing them to focus correctly on the retina.
Q5. Why does the sky appear blue on a clear day? (CBSE 2015)
A. The sky appears blue due to the scattering of light by fine particles and air molecules in the
atmosphere. The shorter wavelengths of light (blue and violet) are scattered more effectively
than the longer wavelengths (red and orange). As sunlight passes through the atmosphere,
the blue light is scattered in all directions, reaching our eyes from every direction, making the
sky appear blue.
Q6. The far point of a myopic person is 80cm in front of the eye. What is the nature and
power of the lens required to correct the defect? (CBSE 2014)
A.
The person needs to see an object at infinity clearly. The image of the object at infinity should
be formed at the far point of the myopic eye.
Object distance, u=−∞
Image distance, v=−80cm=−0.8m
Using the lens formula, f1=v1−u1
f1=−0.81−−∞1=−0.81−0
f1=−1.25D
Power of the lens, P=f1=−1.25D
Nature of the lens: Concave lens.
Q7. A ray of light travelling in air enters an optically denser medium. Does it bend towards or
away from the normal? Why? (CBSE 2013)
A. A ray of light travelling from a rarer medium (air) to a denser medium will bend towards the
normal. This is because the speed of light decreases as it enters an optically denser medium.
Q8. A convex lens forms a real and inverted image of an object at a distance of 40cm from it.
The size of the image is equal to the size of the object. Find the focal length of the lens.
(CBSE 2012)
A. For a real image of the same size as the object, the object must be at a distance of 2f from
the lens. The image will also be formed at a distance of 2f.
Given, image distance, v=+40cm (for a real image)
This means, 2f=40cm
Focal length, f=240=20cm
Q9. Why do stars twinkle but planets do not? (CBSE 2011)
objects (the book) clearly but not distant objects (the blackboard). It can be corrected by
using a concave lens of appropriate power. The concave lens diverges the light rays slightly
before they enter the eye, allowing them to focus correctly on the retina.
Q5. Why does the sky appear blue on a clear day? (CBSE 2015)
A. The sky appears blue due to the scattering of light by fine particles and air molecules in the
atmosphere. The shorter wavelengths of light (blue and violet) are scattered more effectively
than the longer wavelengths (red and orange). As sunlight passes through the atmosphere,
the blue light is scattered in all directions, reaching our eyes from every direction, making the
sky appear blue.
Q6. The far point of a myopic person is 80cm in front of the eye. What is the nature and
power of the lens required to correct the defect? (CBSE 2014)
A.
The person needs to see an object at infinity clearly. The image of the object at infinity should
be formed at the far point of the myopic eye.
Object distance, u=−∞
Image distance, v=−80cm=−0.8m
Using the lens formula, f1=v1−u1
f1=−0.81−−∞1=−0.81−0
f1=−1.25D
Power of the lens, P=f1=−1.25D
Nature of the lens: Concave lens.
Q7. A ray of light travelling in air enters an optically denser medium. Does it bend towards or
away from the normal? Why? (CBSE 2013)
A. A ray of light travelling from a rarer medium (air) to a denser medium will bend towards the
normal. This is because the speed of light decreases as it enters an optically denser medium.
Q8. A convex lens forms a real and inverted image of an object at a distance of 40cm from it.
The size of the image is equal to the size of the object. Find the focal length of the lens.
(CBSE 2012)
A. For a real image of the same size as the object, the object must be at a distance of 2f from
the lens. The image will also be formed at a distance of 2f.
Given, image distance, v=+40cm (for a real image)
This means, 2f=40cm
Focal length, f=240=20cm
Q9. Why do stars twinkle but planets do not? (CBSE 2011)
A. Stars twinkle because they are very far away and appear as point sources of light. The light
from a star undergoes multiple refractions due to the changing density and temperature of
the Earth's atmosphere. This causes the apparent position and brightness of the star to
fluctuate, leading to the twinkling effect. Planets, being much closer, appear as extended
sources. The variations in light from different points of the planet's surface average out, and
the total amount of light entering our eyes remains constant, so they do not appear to
twinkle.
Q10. What is meant by the power of a lens? Write its SI unit. A student uses a lens of power
−2.5D to correct a vision defect. Name the defect and the type of lens used. (CBSE 2019)
A. The power of a lens is a measure of its ability to converge or diverge light. It is defined as
the reciprocal of its focal length in metres. The SI unit of power is the dioptre (D).
A lens with negative power (−2.5D) is a concave lens. A concave lens is used to correct
Myopia (nearsightedness).
Q11. An object is placed at a distance of 10cm from a concave mirror of focal length 20cm.
Find the position of the image and its magnification. (CBSE 2018)
A.
Given:
Object distance, u=−10cm
Focal length, f=−20cm (for a concave mirror)
Using the mirror formula, v1+u1=f1
v1=f1−u1=−201−−101=−201+101
v1=20−1+2=201
v=+20cm
The image is formed at a distance of 20cm behind the mirror. The image is virtual and erect.
Magnification, m=−uv=−−1020=+2
Q12. A ray of light passes from glass to air. Will it bend towards the normal or away from the
normal? Why? (CBSE 2016)
A. The ray of light will bend away from the normal. This is because the speed of light
increases as it travels from an optically denser medium (glass) to a rarer medium (air).
Q13. Name the component of the human eye that regulates the amount of light entering it.
(CBSE 2015)
A. The iris is the component of the human eye that regulates the amount of light entering it. It
automatically adjusts the size of the pupil.
Q14. An object is placed at a distance of 15cm from a convex lens of focal length 10cm. Find
the position and nature of the image formed. (CBSE 2014)
A.
from a star undergoes multiple refractions due to the changing density and temperature of
the Earth's atmosphere. This causes the apparent position and brightness of the star to
fluctuate, leading to the twinkling effect. Planets, being much closer, appear as extended
sources. The variations in light from different points of the planet's surface average out, and
the total amount of light entering our eyes remains constant, so they do not appear to
twinkle.
Q10. What is meant by the power of a lens? Write its SI unit. A student uses a lens of power
−2.5D to correct a vision defect. Name the defect and the type of lens used. (CBSE 2019)
A. The power of a lens is a measure of its ability to converge or diverge light. It is defined as
the reciprocal of its focal length in metres. The SI unit of power is the dioptre (D).
A lens with negative power (−2.5D) is a concave lens. A concave lens is used to correct
Myopia (nearsightedness).
Q11. An object is placed at a distance of 10cm from a concave mirror of focal length 20cm.
Find the position of the image and its magnification. (CBSE 2018)
A.
Given:
Object distance, u=−10cm
Focal length, f=−20cm (for a concave mirror)
Using the mirror formula, v1+u1=f1
v1=f1−u1=−201−−101=−201+101
v1=20−1+2=201
v=+20cm
The image is formed at a distance of 20cm behind the mirror. The image is virtual and erect.
Magnification, m=−uv=−−1020=+2
Q12. A ray of light passes from glass to air. Will it bend towards the normal or away from the
normal? Why? (CBSE 2016)
A. The ray of light will bend away from the normal. This is because the speed of light
increases as it travels from an optically denser medium (glass) to a rarer medium (air).
Q13. Name the component of the human eye that regulates the amount of light entering it.
(CBSE 2015)
A. The iris is the component of the human eye that regulates the amount of light entering it. It
automatically adjusts the size of the pupil.
Q14. An object is placed at a distance of 15cm from a convex lens of focal length 10cm. Find
the position and nature of the image formed. (CBSE 2014)
A.
Given:
Object distance, u=−15cm
Focal length, f=+10cm
Using the lens formula, v1−u1=f1
v1=f1+u1=101+−151=101−151
v1=303−2=301
v=+30cm
The image is formed at a distance of 30cm on the other side of the lens.
Nature of the image: The image is real, inverted, and magnified.
Q15. What is Tyndall effect? Give an example. (CBSE 2011)
A. The Tyndall effect is the scattering of a beam of light by colloidal particles or very fine
suspended particles in a medium.
Example: The path of a beam of light becomes visible when it passes through a dark, dusty
room. The dust particles in the air scatter the light, making its path visible.
Object distance, u=−15cm
Focal length, f=+10cm
Using the lens formula, v1−u1=f1
v1=f1+u1=101+−151=101−151
v1=303−2=301
v=+30cm
The image is formed at a distance of 30cm on the other side of the lens.
Nature of the image: The image is real, inverted, and magnified.
Q15. What is Tyndall effect? Give an example. (CBSE 2011)
A. The Tyndall effect is the scattering of a beam of light by colloidal particles or very fine
suspended particles in a medium.
Example: The path of a beam of light becomes visible when it passes through a dark, dusty
room. The dust particles in the air scatter the light, making its path visible.
CBSE Class 10 Science: The Human Eye
and Colourful World
Part 1: Detailed Notes
The Human Eye: Structure and Functioning
The human eye is one of the most valuable and sensitive sense organs. It is a natural optical
instrument that enables us to see the colourful world around us. It functions much like a
camera.
Key Components of the Eye:
● Cornea: The transparent front part of the eye that refracts light.
● Iris: A muscular diaphragm that controls the size of the pupil.
● Pupil: The black opening in the center of the iris through which light enters the eye.
● Crystalline Lens: A transparent, flexible, biconvex lens that focuses light onto the
retina.
● Ciliary Muscles: Muscles that can alter the curvature (and thus the focal length) of the
eye lens.
● Retina: The light-sensitive screen at the back of the eye where the image is formed.
● Optic Nerve: The nerve that transmits electrical signals from the retina to the brain.
How a Lens in the Human Eye Functions:
The eye lens is a convex lens that forms a real and inverted image of an object on the retina.
The lens is not fixed in position; its curvature and focal length can be adjusted by the ciliary
muscles. This ability of the eye to adjust its focal length to see objects at varying distances is
called accommodation. When viewing a distant object, the ciliary muscles relax, making the
lens thin and its focal length longer. When viewing a nearby object, the muscles contract,
making the lens thicker and its focal length shorter.
Image of the human eye diagram
Defects of Vision and Their Correction
The ability of a normal eye to see objects clearly at all distances is excellent, but sometimes
the eye may lose its power of accommodation, leading to vision defects.
1. Myopia (Nearsightedness):
○ Description: A person with myopia can see nearby objects clearly but cannot see
distant objects distinctly. The far point of a myopic eye is closer than infinity.
○ Causes:
and Colourful World
Part 1: Detailed Notes
The Human Eye: Structure and Functioning
The human eye is one of the most valuable and sensitive sense organs. It is a natural optical
instrument that enables us to see the colourful world around us. It functions much like a
camera.
Key Components of the Eye:
● Cornea: The transparent front part of the eye that refracts light.
● Iris: A muscular diaphragm that controls the size of the pupil.
● Pupil: The black opening in the center of the iris through which light enters the eye.
● Crystalline Lens: A transparent, flexible, biconvex lens that focuses light onto the
retina.
● Ciliary Muscles: Muscles that can alter the curvature (and thus the focal length) of the
eye lens.
● Retina: The light-sensitive screen at the back of the eye where the image is formed.
● Optic Nerve: The nerve that transmits electrical signals from the retina to the brain.
How a Lens in the Human Eye Functions:
The eye lens is a convex lens that forms a real and inverted image of an object on the retina.
The lens is not fixed in position; its curvature and focal length can be adjusted by the ciliary
muscles. This ability of the eye to adjust its focal length to see objects at varying distances is
called accommodation. When viewing a distant object, the ciliary muscles relax, making the
lens thin and its focal length longer. When viewing a nearby object, the muscles contract,
making the lens thicker and its focal length shorter.
Image of the human eye diagram
Defects of Vision and Their Correction
The ability of a normal eye to see objects clearly at all distances is excellent, but sometimes
the eye may lose its power of accommodation, leading to vision defects.
1. Myopia (Nearsightedness):
○ Description: A person with myopia can see nearby objects clearly but cannot see
distant objects distinctly. The far point of a myopic eye is closer than infinity.
○ Causes:
■ Excessive curvature of the eye lens.
■ Elongation of the eyeball.
○ Correction: It can be corrected by using a concave lens of appropriate power. The
concave lens diverges the light rays, allowing the final image to be formed on the
retina.
2. Hypermetropia (Farsightedness):
○ Description: A person with hypermetropia can see distant objects clearly but has
difficulty viewing nearby objects. The near point of the eye is farther away from the
normal near point of 25cm.
○ Causes:
■ The eye lens's focal length is too long.
■ The eyeball is too short.
○ Correction: It can be corrected by using a convex lens of appropriate power. The
convex lens converges the light rays before they enter the eye, ensuring the final
image is formed on the retina.
Refraction of Light Through a Prism
A prism is a transparent refracting medium with at least two non-parallel plane surfaces.
When a ray of light passes through a prism, it bends towards the base of the prism. The angle
between the incident ray and the emergent ray is known as the angle of deviation (δ).
Dispersion of White Light by a Glass Prism
Dispersion is the phenomenon of a beam of white light splitting into its seven constituent
colours (VIBGYOR) upon passing through a prism. This happens because each colour of light
has a different wavelength and, therefore, a different speed in the prism's medium. As a
result, each colour bends at a slightly different angle, leading to their separation.
The sequence of colours in the spectrum is VIBGYOR (Violet, Indigo, Blue, Green, Yellow,
Orange, Red). Violet light bends the most, and red light bends the least. This is because the
refractive index of glass is slightly different for each colour.
Atmospheric Refraction and Scattering of Light
● Atmospheric Refraction: The bending of light as it passes through the Earth's
atmosphere due to the varying refractive indices of different atmospheric layers. This is
responsible for phenomena like the twinkling of stars.
● Scattering of Light: The redirection of light rays by minute particles in the atmosphere.
The amount of scattering depends on the wavelength of light and the size of the
scattering particles.
● Why the Sky Appears Blue: The fine air molecules in the atmosphere scatter shorter
wavelengths (blue and violet) much more effectively than longer wavelengths (red). This
■ Elongation of the eyeball.
○ Correction: It can be corrected by using a concave lens of appropriate power. The
concave lens diverges the light rays, allowing the final image to be formed on the
retina.
2. Hypermetropia (Farsightedness):
○ Description: A person with hypermetropia can see distant objects clearly but has
difficulty viewing nearby objects. The near point of the eye is farther away from the
normal near point of 25cm.
○ Causes:
■ The eye lens's focal length is too long.
■ The eyeball is too short.
○ Correction: It can be corrected by using a convex lens of appropriate power. The
convex lens converges the light rays before they enter the eye, ensuring the final
image is formed on the retina.
Refraction of Light Through a Prism
A prism is a transparent refracting medium with at least two non-parallel plane surfaces.
When a ray of light passes through a prism, it bends towards the base of the prism. The angle
between the incident ray and the emergent ray is known as the angle of deviation (δ).
Dispersion of White Light by a Glass Prism
Dispersion is the phenomenon of a beam of white light splitting into its seven constituent
colours (VIBGYOR) upon passing through a prism. This happens because each colour of light
has a different wavelength and, therefore, a different speed in the prism's medium. As a
result, each colour bends at a slightly different angle, leading to their separation.
The sequence of colours in the spectrum is VIBGYOR (Violet, Indigo, Blue, Green, Yellow,
Orange, Red). Violet light bends the most, and red light bends the least. This is because the
refractive index of glass is slightly different for each colour.
Atmospheric Refraction and Scattering of Light
● Atmospheric Refraction: The bending of light as it passes through the Earth's
atmosphere due to the varying refractive indices of different atmospheric layers. This is
responsible for phenomena like the twinkling of stars.
● Scattering of Light: The redirection of light rays by minute particles in the atmosphere.
The amount of scattering depends on the wavelength of light and the size of the
scattering particles.
● Why the Sky Appears Blue: The fine air molecules in the atmosphere scatter shorter
wavelengths (blue and violet) much more effectively than longer wavelengths (red). This
scattered blue light reaches our eyes from all directions, making the sky appear blue.
Part 2: Previous Year's Questions (PYQs)
Q1. What is meant by the power of accommodation of the eye? (CBSE 2017)
A. The power of accommodation of the eye is the ability of the eye lens to adjust its focal
length. This allows the eye to form a clear image of objects located at varying distances on
the retina.
Q2. The near point of a person is 75cm. Name the defect of vision and the type of lens
required to correct it. (CBSE 2018)
A. The person's near point is greater than the normal 25cm, which means they are suffering
from hypermetropia (farsightedness). This can be corrected using a convex lens of
appropriate power.
Q3. A student sitting in the last row of the classroom cannot read the writing on the
blackboard clearly but can read a book. Name the defect of vision and how can it be
corrected? (CBSE 2019)
A. The student is suffering from myopia (nearsightedness). This is because they can see
nearby objects (the book) but not distant objects (the blackboard). It can be corrected by
using a concave lens of appropriate power.
Q4. Why does a prism split white light into its constituent colours? (CBSE 2016)
A. White light is composed of seven colours. A prism splits white light because the refractive
index of the glass is slightly different for each colour (or wavelength). This causes each
colour to bend at a different angle as it passes through the prism, leading to the separation
of colours and the formation of a spectrum.
Q5. Why do stars twinkle but planets do not? (CBSE 2011)
A. Stars twinkle because they are very far away and act as point sources of light. The light
from a star undergoes continuous refraction as it passes through the turbulent and varying
atmosphere, causing the apparent position and brightness of the star to fluctuate. Planets,
being much closer, act as extended sources of light. The light from a planet is the sum of light
from many point sources. The effects of atmospheric refraction are averaged out, and the
total amount of light entering our eyes remains constant, so planets do not twinkle.
Q6. The far point of a myopic person is 80cm in front of the eye. What is the nature and
power of the lens required to correct the defect? (CBSE 2014)
A. The person needs to see an object at infinity clearly. The image of the object at infinity
should be formed at the far point of the eye.
● Object distance, u=−∞
● Image distance, v=−80cm=−0.8m
Using the lens formula, f1=v1−u1
f1=−0.81−−∞1=−1.25−0P=f1=−1.25D
The negative power indicates a concave lens.
Part 2: Previous Year's Questions (PYQs)
Q1. What is meant by the power of accommodation of the eye? (CBSE 2017)
A. The power of accommodation of the eye is the ability of the eye lens to adjust its focal
length. This allows the eye to form a clear image of objects located at varying distances on
the retina.
Q2. The near point of a person is 75cm. Name the defect of vision and the type of lens
required to correct it. (CBSE 2018)
A. The person's near point is greater than the normal 25cm, which means they are suffering
from hypermetropia (farsightedness). This can be corrected using a convex lens of
appropriate power.
Q3. A student sitting in the last row of the classroom cannot read the writing on the
blackboard clearly but can read a book. Name the defect of vision and how can it be
corrected? (CBSE 2019)
A. The student is suffering from myopia (nearsightedness). This is because they can see
nearby objects (the book) but not distant objects (the blackboard). It can be corrected by
using a concave lens of appropriate power.
Q4. Why does a prism split white light into its constituent colours? (CBSE 2016)
A. White light is composed of seven colours. A prism splits white light because the refractive
index of the glass is slightly different for each colour (or wavelength). This causes each
colour to bend at a different angle as it passes through the prism, leading to the separation
of colours and the formation of a spectrum.
Q5. Why do stars twinkle but planets do not? (CBSE 2011)
A. Stars twinkle because they are very far away and act as point sources of light. The light
from a star undergoes continuous refraction as it passes through the turbulent and varying
atmosphere, causing the apparent position and brightness of the star to fluctuate. Planets,
being much closer, act as extended sources of light. The light from a planet is the sum of light
from many point sources. The effects of atmospheric refraction are averaged out, and the
total amount of light entering our eyes remains constant, so planets do not twinkle.
Q6. The far point of a myopic person is 80cm in front of the eye. What is the nature and
power of the lens required to correct the defect? (CBSE 2014)
A. The person needs to see an object at infinity clearly. The image of the object at infinity
should be formed at the far point of the eye.
● Object distance, u=−∞
● Image distance, v=−80cm=−0.8m
Using the lens formula, f1=v1−u1
f1=−0.81−−∞1=−1.25−0P=f1=−1.25D
The negative power indicates a concave lens.
Q7. Name the component of the human eye that regulates the amount of light entering it.
(CBSE 2015)
A. The iris is the component of the human eye that regulates the amount of light entering it. It
automatically adjusts the size of the pupil, which acts as the aperture.
Q8. What is the Tyndall effect? Give an example. (CBSE 2011)
A. The Tyndall effect is the scattering of a beam of light by very fine suspended particles in a
medium.
Example: The path of a beam of light becomes visible when it passes through a dusty room or
a misty forest. The dust or mist particles scatter the light, making its path visible.
Q9. Why does the sky appear blue on a clear day? (CBSE 2015)
A. The sky appears blue due to the scattering of light by fine air molecules in the atmosphere.
The shorter wavelengths of visible light, especially blue, are scattered much more efficiently
than the longer wavelengths, such as red. This scattered blue light reaches our eyes from all
directions.
Q10. A person needs a lens of power −4.5D for correction of vision. What kind of defect is he
suffering from? (CBSE 2019)
A. The negative power indicates a concave lens. A concave lens is used to correct myopia
(nearsightedness).
Q11. State the cause of dispersion of white light. (CBSE 2012)
A. The cause of dispersion is that the refractive index of the medium (e.g., glass of the prism)
is different for different wavelengths of light. This causes each colour to travel at a slightly
different speed and bend at a different angle upon entering and leaving the prism, leading to
their separation.
Q12. What is the principal cause of twinkling of stars? (CBSE 2018)
A. The twinkling of stars is caused by atmospheric refraction. The light from a distant star
travels through the atmosphere with varying layers of air density and temperature. This
continuous change in the refractive index of the atmosphere causes the light to randomly
bend, making the star appear to twinkle.
Q13. What is the function of the crystalline eye lens in the human eye? (CBSE 2016)
A. The crystalline eye lens is responsible for focusing light onto the retina. Its unique ability to
change its focal length through the action of the ciliary muscles allows the eye to focus on
both near and distant objects.
Q14. A student finds that the image of a distant tree is formed at the far point of his eye.
Name the defect of vision and suggest a lens to correct it. (CBSE 2017)
A. The student's far point is not at infinity, which is a symptom of myopia. The image of a
distant object is formed in front of the retina. This defect can be corrected by using a
concave lens.
Q15. The pupil of an eye is black. Why? (CBSE 2013)
A. The pupil appears black because almost all the light entering it is absorbed by the retina.
No light is reflected back from the eye, making the pupil appear black.
(CBSE 2015)
A. The iris is the component of the human eye that regulates the amount of light entering it. It
automatically adjusts the size of the pupil, which acts as the aperture.
Q8. What is the Tyndall effect? Give an example. (CBSE 2011)
A. The Tyndall effect is the scattering of a beam of light by very fine suspended particles in a
medium.
Example: The path of a beam of light becomes visible when it passes through a dusty room or
a misty forest. The dust or mist particles scatter the light, making its path visible.
Q9. Why does the sky appear blue on a clear day? (CBSE 2015)
A. The sky appears blue due to the scattering of light by fine air molecules in the atmosphere.
The shorter wavelengths of visible light, especially blue, are scattered much more efficiently
than the longer wavelengths, such as red. This scattered blue light reaches our eyes from all
directions.
Q10. A person needs a lens of power −4.5D for correction of vision. What kind of defect is he
suffering from? (CBSE 2019)
A. The negative power indicates a concave lens. A concave lens is used to correct myopia
(nearsightedness).
Q11. State the cause of dispersion of white light. (CBSE 2012)
A. The cause of dispersion is that the refractive index of the medium (e.g., glass of the prism)
is different for different wavelengths of light. This causes each colour to travel at a slightly
different speed and bend at a different angle upon entering and leaving the prism, leading to
their separation.
Q12. What is the principal cause of twinkling of stars? (CBSE 2018)
A. The twinkling of stars is caused by atmospheric refraction. The light from a distant star
travels through the atmosphere with varying layers of air density and temperature. This
continuous change in the refractive index of the atmosphere causes the light to randomly
bend, making the star appear to twinkle.
Q13. What is the function of the crystalline eye lens in the human eye? (CBSE 2016)
A. The crystalline eye lens is responsible for focusing light onto the retina. Its unique ability to
change its focal length through the action of the ciliary muscles allows the eye to focus on
both near and distant objects.
Q14. A student finds that the image of a distant tree is formed at the far point of his eye.
Name the defect of vision and suggest a lens to correct it. (CBSE 2017)
A. The student's far point is not at infinity, which is a symptom of myopia. The image of a
distant object is formed in front of the retina. This defect can be corrected by using a
concave lens.
Q15. The pupil of an eye is black. Why? (CBSE 2013)
A. The pupil appears black because almost all the light entering it is absorbed by the retina.
No light is reflected back from the eye, making the pupil appear black.
CBSE Class 10 Science: Electricity
Part 1: Detailed Notes
Introduction to Electric Current and Circuit
Electric Current: An electric current is defined as the flow of electric charges. The direction of
conventional current is from the positive terminal to the negative terminal of a cell or battery.
The magnitude of electric current is the amount of charge (Q) flowing through a particular
area in a unit time (t).
I=tQ
The SI unit of electric current is the ampere (A), named after the French scientist André-
Marie Ampère. One ampere is defined as one coulomb of charge flowing per second.
Electric Circuit: An electric circuit is a continuous and closed path of an electric current. It
consists of a cell, a key or switch, and other components connected by wires. A circuit is
considered an open circuit when the switch is open and no current flows. A closed circuit is
one where the switch is closed and current flows.
Potential Difference and Ohm's Law
Electric Potential Difference: The electric potential difference between two points in an
electric circuit is the work done (W) to move a unit charge (Q) from one point to the other.
V=QW
The SI unit of potential difference is the volt (V), named after Alessandro Volta. One volt is
the potential difference between two points in a current-carrying conductor when 1 joule of
work is done to move a charge of 1 coulomb from one point to another.
Ohm's Law: This law states that the potential difference (V) across the ends of a given
metallic wire in an electric circuit is directly proportional to the current (I) flowing through it,
provided its temperature remains constant.
V∝IorV=IR
Here, R is the constant of proportionality called resistance.
Resistance and Resistivity
Resistance: The property of a conductor to resist the flow of charges through it is called
resistance. The SI unit of resistance is the ohm (Ω).
Factors Affecting Resistance: The resistance of a uniform metallic conductor depends on:
1. Length (l): Resistance is directly proportional to the length of the conductor (R∝l).
Part 1: Detailed Notes
Introduction to Electric Current and Circuit
Electric Current: An electric current is defined as the flow of electric charges. The direction of
conventional current is from the positive terminal to the negative terminal of a cell or battery.
The magnitude of electric current is the amount of charge (Q) flowing through a particular
area in a unit time (t).
I=tQ
The SI unit of electric current is the ampere (A), named after the French scientist André-
Marie Ampère. One ampere is defined as one coulomb of charge flowing per second.
Electric Circuit: An electric circuit is a continuous and closed path of an electric current. It
consists of a cell, a key or switch, and other components connected by wires. A circuit is
considered an open circuit when the switch is open and no current flows. A closed circuit is
one where the switch is closed and current flows.
Potential Difference and Ohm's Law
Electric Potential Difference: The electric potential difference between two points in an
electric circuit is the work done (W) to move a unit charge (Q) from one point to the other.
V=QW
The SI unit of potential difference is the volt (V), named after Alessandro Volta. One volt is
the potential difference between two points in a current-carrying conductor when 1 joule of
work is done to move a charge of 1 coulomb from one point to another.
Ohm's Law: This law states that the potential difference (V) across the ends of a given
metallic wire in an electric circuit is directly proportional to the current (I) flowing through it,
provided its temperature remains constant.
V∝IorV=IR
Here, R is the constant of proportionality called resistance.
Resistance and Resistivity
Resistance: The property of a conductor to resist the flow of charges through it is called
resistance. The SI unit of resistance is the ohm (Ω).
Factors Affecting Resistance: The resistance of a uniform metallic conductor depends on:
1. Length (l): Resistance is directly proportional to the length of the conductor (R∝l).
2. Area of Cross-section (A): Resistance is inversely proportional to the area of cross-
section (R∝A1).
3. Nature of the Material: Resistance depends on the material of the conductor.
Combining these factors, we get the relationship:
R=ρAl
Here, ρ (rho) is the constant of proportionality called resistivity. Its SI unit is ohm-metre
(Ωm).
Resistors in Series and Parallel
Resistors in Series: When two or more resistors are connected end-to-end, they are said to
be in series. The total equivalent resistance (RS) is the sum of the individual resistances. The
current is the same in every part of the circuit.
RS=R1+R2+⋯+Rn
Resistors in Parallel: When two or more resistors are connected between the same two
points, they are said to be in parallel. The reciprocal of the equivalent resistance (RP) is the
sum of the reciprocals of the individual resistances. The potential difference across each
resistor is the same.
RP1=R11+R21+⋯+Rn1
Heating Effect of Electric Current and Electric Power
Joule's Law of Heating: When an electric current passes through a resistor, it dissipates
energy as heat. This is known as the heating effect of electric current. Joule's Law states that
the heat produced (H) in a resistor is:
1. Directly proportional to the square of the current (I2).
2. Directly proportional to the resistance of the conductor (R).
3. Directly proportional to the time for which the current flows (t).
H=I2Rt
The SI unit of heat is joule (J).
Electric Power: Electric power is the rate at which electrical energy is consumed in an
electric circuit.
P=VIorP=I2RorP=RV2
The SI unit of electric power is the watt (W). One watt is the power consumed by a device
that carries 1 A of current when the potential difference across it is 1 V. The commercial unit
of electrical energy is the kilowatt-hour (kWh).
1kWh=3.6×106J
section (R∝A1).
3. Nature of the Material: Resistance depends on the material of the conductor.
Combining these factors, we get the relationship:
R=ρAl
Here, ρ (rho) is the constant of proportionality called resistivity. Its SI unit is ohm-metre
(Ωm).
Resistors in Series and Parallel
Resistors in Series: When two or more resistors are connected end-to-end, they are said to
be in series. The total equivalent resistance (RS) is the sum of the individual resistances. The
current is the same in every part of the circuit.
RS=R1+R2+⋯+Rn
Resistors in Parallel: When two or more resistors are connected between the same two
points, they are said to be in parallel. The reciprocal of the equivalent resistance (RP) is the
sum of the reciprocals of the individual resistances. The potential difference across each
resistor is the same.
RP1=R11+R21+⋯+Rn1
Heating Effect of Electric Current and Electric Power
Joule's Law of Heating: When an electric current passes through a resistor, it dissipates
energy as heat. This is known as the heating effect of electric current. Joule's Law states that
the heat produced (H) in a resistor is:
1. Directly proportional to the square of the current (I2).
2. Directly proportional to the resistance of the conductor (R).
3. Directly proportional to the time for which the current flows (t).
H=I2Rt
The SI unit of heat is joule (J).
Electric Power: Electric power is the rate at which electrical energy is consumed in an
electric circuit.
P=VIorP=I2RorP=RV2
The SI unit of electric power is the watt (W). One watt is the power consumed by a device
that carries 1 A of current when the potential difference across it is 1 V. The commercial unit
of electrical energy is the kilowatt-hour (kWh).
1kWh=3.6×106J
Part 2: Previous Year's Questions (PYQs)
Q1. What is the SI unit of electric potential difference? Define it. (CBSE 2017)
A. The SI unit of electric potential difference is the volt (V). One volt is the potential difference
between two points in a circuit when 1 joule of work is done to move a 1-coulomb charge from
one point to the other.
Q2. An electric circuit consists of a 0.5m long nichrome wire, an ammeter, a voltmeter, and a
battery. The ammeter shows a reading of 0.5A and the voltmeter shows a reading of 2.5V.
Find the resistance of the nichrome wire. (CBSE 2016)
A.
Given: I=0.5A, V=2.5V.
Using Ohm's Law, V=IR.
R=IV=0.5A2.5V=5Ω
Q3. An electric iron of resistance 20Ω takes a current of 5A. Calculate the heat developed in
30s. (CBSE 2018)
A.
Given: R=20Ω, I=5A, t=30s.
Using Joule's Law of Heating, H=I2Rt.
H = (5A)2 × (20 Ω) × (30 s) = 15000 J
Q4. What is the commercial unit of electrical energy? Express it in joules. (CBSE 2015)
A. The commercial unit of electrical energy is the kilowatt-hour (kWh).
1 kWh = 1 kW × 1h = (1000 W) × (3600 s) = 3.6 × 106 J
Q5. How is a voltmeter connected in a circuit to measure the potential difference? (CBSE
2019)
A. A voltmeter is always connected in parallel across the two points between which the
potential difference is to be measured.
Q6. Define the term resistance. What is the unit of resistivity? (CBSE 2017)
A. Resistance is the property of a conductor that opposes the flow of electric current.
The unit of resistivity is ohm-metre (Ωm).
Q7. A student has to connect four resistors of 2Ω each to form a network with an equivalent
resistance of 2Ω. How should he connect them? (CBSE 2014, Modified)
A. The student should connect two pairs of resistors in parallel. Each parallel pair will have an
Q1. What is the SI unit of electric potential difference? Define it. (CBSE 2017)
A. The SI unit of electric potential difference is the volt (V). One volt is the potential difference
between two points in a circuit when 1 joule of work is done to move a 1-coulomb charge from
one point to the other.
Q2. An electric circuit consists of a 0.5m long nichrome wire, an ammeter, a voltmeter, and a
battery. The ammeter shows a reading of 0.5A and the voltmeter shows a reading of 2.5V.
Find the resistance of the nichrome wire. (CBSE 2016)
A.
Given: I=0.5A, V=2.5V.
Using Ohm's Law, V=IR.
R=IV=0.5A2.5V=5Ω
Q3. An electric iron of resistance 20Ω takes a current of 5A. Calculate the heat developed in
30s. (CBSE 2018)
A.
Given: R=20Ω, I=5A, t=30s.
Using Joule's Law of Heating, H=I2Rt.
H = (5A)2 × (20 Ω) × (30 s) = 15000 J
Q4. What is the commercial unit of electrical energy? Express it in joules. (CBSE 2015)
A. The commercial unit of electrical energy is the kilowatt-hour (kWh).
1 kWh = 1 kW × 1h = (1000 W) × (3600 s) = 3.6 × 106 J
Q5. How is a voltmeter connected in a circuit to measure the potential difference? (CBSE
2019)
A. A voltmeter is always connected in parallel across the two points between which the
potential difference is to be measured.
Q6. Define the term resistance. What is the unit of resistivity? (CBSE 2017)
A. Resistance is the property of a conductor that opposes the flow of electric current.
The unit of resistivity is ohm-metre (Ωm).
Q7. A student has to connect four resistors of 2Ω each to form a network with an equivalent
resistance of 2Ω. How should he connect them? (CBSE 2014, Modified)
A. The student should connect two pairs of resistors in parallel. Each parallel pair will have an
equivalent resistance of RP=1/2+1/21=1Ω. Then, connect these two parallel combinations in
series with each other. The total equivalent resistance will be RS=1Ω+1Ω=2Ω.
Q8. A bulb is rated 220V and 100W. When it is operated on 110V, what is the power
consumed? (CBSE 2013)
A.
First, calculate the resistance of the bulb using its given ratings.
P=RV2⟹R=PV2=100W(220V)2=484Ω
Now, calculate the power consumed at the new voltage.
P=RV2=484Ω(110V)2=25W
Q9. Why are copper wires used as connecting wires? (CBSE 2012)
A. Copper wires are used as connecting wires because copper has a very low resistivity,
making it an excellent conductor of electricity. This allows current to flow with minimal loss of
energy in the form of heat.
Q10. Differentiate between resistance and resistivity. (CBSE 2011)
A. Resistance is the property of a specific conductor to oppose the flow of current. It
depends on the length, area, and nature of the material. Its unit is the ohm (Ω).
Resistivity is an intrinsic property of a material itself. It is the resistance of a conductor of unit
length and unit area of cross-section. It does not depend on the dimensions of the
conductor. Its unit is ohm-metre (Ωm).
Q11. What is the relationship between the potential difference, current, and resistance in a
circuit? Name the law. (CBSE 2019)
A. The relationship is given by Ohm's Law, which states that potential difference is directly
proportional to the current. The equation is V=IR.
Q12. What is the maximum number of 100Ω resistors that can be connected in parallel to a
200V line if the total current is not to exceed 10A? (CBSE 2018, Modified)
A.
Minimum equivalent resistance required, Req=ImaxV=10A200V=20Ω.
For n resistors in parallel: Req1=Rn.
201=100n⟹n=20100=5
The maximum number of resistors is 5.
series with each other. The total equivalent resistance will be RS=1Ω+1Ω=2Ω.
Q8. A bulb is rated 220V and 100W. When it is operated on 110V, what is the power
consumed? (CBSE 2013)
A.
First, calculate the resistance of the bulb using its given ratings.
P=RV2⟹R=PV2=100W(220V)2=484Ω
Now, calculate the power consumed at the new voltage.
P=RV2=484Ω(110V)2=25W
Q9. Why are copper wires used as connecting wires? (CBSE 2012)
A. Copper wires are used as connecting wires because copper has a very low resistivity,
making it an excellent conductor of electricity. This allows current to flow with minimal loss of
energy in the form of heat.
Q10. Differentiate between resistance and resistivity. (CBSE 2011)
A. Resistance is the property of a specific conductor to oppose the flow of current. It
depends on the length, area, and nature of the material. Its unit is the ohm (Ω).
Resistivity is an intrinsic property of a material itself. It is the resistance of a conductor of unit
length and unit area of cross-section. It does not depend on the dimensions of the
conductor. Its unit is ohm-metre (Ωm).
Q11. What is the relationship between the potential difference, current, and resistance in a
circuit? Name the law. (CBSE 2019)
A. The relationship is given by Ohm's Law, which states that potential difference is directly
proportional to the current. The equation is V=IR.
Q12. What is the maximum number of 100Ω resistors that can be connected in parallel to a
200V line if the total current is not to exceed 10A? (CBSE 2018, Modified)
A.
Minimum equivalent resistance required, Req=ImaxV=10A200V=20Ω.
For n resistors in parallel: Req1=Rn.
201=100n⟹n=20100=5
The maximum number of resistors is 5.
Q13. An electric heater of resistance 8Ω draws 15A from the service mains for 2 hours.
Calculate the cost of operating the heater if the rate is Rs. 3.00 per kWh. (CBSE 2017)
A.
First, calculate the power of the heater.
P=I2R=(15A)2×(8Ω)=1800W=1.8kW
Now, calculate the energy consumed.
Energy = Power × Time = 1.8kW×2h=3.6kWh.
Cost = Energy consumed × Rate = 3.6kWh×Rs. 3.00/kWh=Rs. 10.80.
Q14. Name an instrument used to measure electric current. How is it connected in a circuit?
(CBSE 2016)
A. An ammeter is used to measure electric current. It is always connected in series in the
circuit to measure the current flowing through it.
Q15. What is the total resistance when two resistors of 5Ω and 10Ω are connected in parallel?
(CBSE 2015)
A.
Using the parallel resistance formula:
RP1=R11+R21=51+101=102+1=103RP=310≈3.33Ω
Calculate the cost of operating the heater if the rate is Rs. 3.00 per kWh. (CBSE 2017)
A.
First, calculate the power of the heater.
P=I2R=(15A)2×(8Ω)=1800W=1.8kW
Now, calculate the energy consumed.
Energy = Power × Time = 1.8kW×2h=3.6kWh.
Cost = Energy consumed × Rate = 3.6kWh×Rs. 3.00/kWh=Rs. 10.80.
Q14. Name an instrument used to measure electric current. How is it connected in a circuit?
(CBSE 2016)
A. An ammeter is used to measure electric current. It is always connected in series in the
circuit to measure the current flowing through it.
Q15. What is the total resistance when two resistors of 5Ω and 10Ω are connected in parallel?
(CBSE 2015)
A.
Using the parallel resistance formula:
RP1=R11+R21=51+101=102+1=103RP=310≈3.33Ω
CBSE Class 10 Science: Magnetic Effects
of Current
Part 1: Detailed Notes
Magnetic Field and Field Lines
A magnetic field is the region surrounding a magnet or a current-carrying conductor where
its magnetic force can be detected.
Magnetic field lines are imaginary lines that represent the direction and strength of a
magnetic field.
● The lines emerge from the North pole and merge into the South pole of a magnet.
● Inside the magnet, the direction of field lines is from the South pole to the North pole,
forming closed loops.
● The field lines never intersect each other.
● The closer the field lines are, the stronger the magnetic field.
Magnetic Field due to Electric Current
A magnetic field is produced whenever an electric current flows through a conductor.
Magnetic Field due to a Straight Conductor:
The magnetic field lines around a straight current-carrying conductor are concentric circles,
centered on the wire. The direction of these circles can be determined using the Right-Hand
Thumb Rule.
of Current
Part 1: Detailed Notes
Magnetic Field and Field Lines
A magnetic field is the region surrounding a magnet or a current-carrying conductor where
its magnetic force can be detected.
Magnetic field lines are imaginary lines that represent the direction and strength of a
magnetic field.
● The lines emerge from the North pole and merge into the South pole of a magnet.
● Inside the magnet, the direction of field lines is from the South pole to the North pole,
forming closed loops.
● The field lines never intersect each other.
● The closer the field lines are, the stronger the magnetic field.
Magnetic Field due to Electric Current
A magnetic field is produced whenever an electric current flows through a conductor.
Magnetic Field due to a Straight Conductor:
The magnetic field lines around a straight current-carrying conductor are concentric circles,
centered on the wire. The direction of these circles can be determined using the Right-Hand
Thumb Rule.
● Right-Hand Thumb Rule: If you hold a current-carrying conductor in your right hand
with your thumb pointing in the direction of the current, your fingers will curl in the
direction of the magnetic field lines.
Magnetic Field due to a Circular Coil:
For a circular coil, the magnetic field lines are concentric circles near the wire. As you move
towards the center of the coil, the circles become larger, and the field lines at the center are
almost straight, forming a uniform magnetic field.
Magnetic Field due to a Solenoid:
A solenoid is a coil of many turns of insulated copper wire closely wound in the shape of a
cylinder. The magnetic field produced by a solenoid is similar to that of a bar magnet. The
field lines inside the solenoid are parallel to the axis, indicating a uniform magnetic field.
Force on a Current-Carrying Conductor
A current-carrying conductor placed in a magnetic field experiences a force. The direction of
this force depends on the direction of the current and the direction of the magnetic field. This
principle is the basis for the electric motor.
The direction of the force is perpendicular to both the direction of the current and the
magnetic field. This can be determined by Fleming’s Left-Hand Rule.
Fleming’s Left-Hand Rule:
Stretch the thumb, forefinger, and middle finger of your left hand so that they are mutually
perpendicular.
● The forefinger points in the direction of the magnetic field.
with your thumb pointing in the direction of the current, your fingers will curl in the
direction of the magnetic field lines.
Magnetic Field due to a Circular Coil:
For a circular coil, the magnetic field lines are concentric circles near the wire. As you move
towards the center of the coil, the circles become larger, and the field lines at the center are
almost straight, forming a uniform magnetic field.
Magnetic Field due to a Solenoid:
A solenoid is a coil of many turns of insulated copper wire closely wound in the shape of a
cylinder. The magnetic field produced by a solenoid is similar to that of a bar magnet. The
field lines inside the solenoid are parallel to the axis, indicating a uniform magnetic field.
Force on a Current-Carrying Conductor
A current-carrying conductor placed in a magnetic field experiences a force. The direction of
this force depends on the direction of the current and the direction of the magnetic field. This
principle is the basis for the electric motor.
The direction of the force is perpendicular to both the direction of the current and the
magnetic field. This can be determined by Fleming’s Left-Hand Rule.
Fleming’s Left-Hand Rule:
Stretch the thumb, forefinger, and middle finger of your left hand so that they are mutually
perpendicular.
● The forefinger points in the direction of the magnetic field.
● The middle finger points in the direction of the current.
● The thumb will then point in the direction of the force or motion.
Direct Current (DC) and Alternating Current (AC)
● Direct Current (DC): A current that flows only in one direction. Sources of DC include
batteries and solar cells.
● Alternating Current (AC): A current that periodically reverses its direction. In India, AC
changes direction every 1001 of a second, so the frequency is 50 Hz.
Advantages of AC over DC:
● AC can be transmitted over long distances with minimal energy loss.
● The voltage of AC can be easily changed using transformers.
Domestic Electric Circuits
Domestic circuits are arranged in a parallel combination to ensure that each appliance
receives the same voltage, and if one appliance fails, the others continue to work.
Wires in a Domestic Circuit:
● Live Wire (Red): Carries the electric current. It is at a high potential (typically 220 V in
India).
● Neutral Wire (Black): Completes the circuit and is at zero potential.
● Earth Wire (Green): A safety wire connected to the ground. It prevents electric shocks
● The thumb will then point in the direction of the force or motion.
Direct Current (DC) and Alternating Current (AC)
● Direct Current (DC): A current that flows only in one direction. Sources of DC include
batteries and solar cells.
● Alternating Current (AC): A current that periodically reverses its direction. In India, AC
changes direction every 1001 of a second, so the frequency is 50 Hz.
Advantages of AC over DC:
● AC can be transmitted over long distances with minimal energy loss.
● The voltage of AC can be easily changed using transformers.
Domestic Electric Circuits
Domestic circuits are arranged in a parallel combination to ensure that each appliance
receives the same voltage, and if one appliance fails, the others continue to work.
Wires in a Domestic Circuit:
● Live Wire (Red): Carries the electric current. It is at a high potential (typically 220 V in
India).
● Neutral Wire (Black): Completes the circuit and is at zero potential.
● Earth Wire (Green): A safety wire connected to the ground. It prevents electric shocks
by providing a low-resistance path for the current in case of a fault.
Safety Devices:
● Fuse: A safety device that protects an electric circuit from damage due to excessive
current (overloading). It has a low melting point, so it breaks the circuit when the current
exceeds a certain limit.
● Earthing: A process of connecting the metallic body of an electrical appliance to the
earth to prevent electric shocks.
Part 2: Previous Year's Questions (PYQs)
Q1. State the Right-Hand Thumb Rule. (CBSE 2011)
A. The Right-Hand Thumb Rule states that if you hold a current-carrying straight conductor in
your right hand with your thumb pointing in the direction of the current, your fingers will curl
around the conductor in the direction of the magnetic field lines.
Q2. An electric motor takes a current of 5A from a 220V supply. Calculate the power and
energy consumed in 2 hours. (CBSE 2012)
A.
Given: I=5A, V=220V, t=2h.
Power, P=VI=220V×5A=1100W=1.1kW.
Energy consumed = Power × Time = 1.1kW×2h=2.2kWh.
Q3. What is the function of an earth wire? (CBSE 2013)
A. The earth wire is a safety device that connects the metallic body of an appliance to the
ground. In case of a fault where the live wire touches the metal casing, the current flows to
the earth, preventing the user from getting an electric shock.
Q4. What is the difference between an AC and DC supply? (CBSE 2014)
A. Direct current (DC) flows in only one direction, while alternating current (AC) periodically
reverses its direction. The frequency of AC is 50 Hz in India.
Q5. What is a solenoid? How does it behave like a magnet? (CBSE 2015)
A. A solenoid is a cylindrical coil of many turns of insulated wire. It behaves like a bar magnet
when a current is passed through it. One end acts as a North pole, and the other acts as a
South pole.
Q6. The magnetic field lines inside a current-carrying solenoid are:
(a) straight
(b) parallel to the axis of the solenoid
(c) straight and parallel to the axis of the solenoid
(d) all of the above (CBSE 2016)
Safety Devices:
● Fuse: A safety device that protects an electric circuit from damage due to excessive
current (overloading). It has a low melting point, so it breaks the circuit when the current
exceeds a certain limit.
● Earthing: A process of connecting the metallic body of an electrical appliance to the
earth to prevent electric shocks.
Part 2: Previous Year's Questions (PYQs)
Q1. State the Right-Hand Thumb Rule. (CBSE 2011)
A. The Right-Hand Thumb Rule states that if you hold a current-carrying straight conductor in
your right hand with your thumb pointing in the direction of the current, your fingers will curl
around the conductor in the direction of the magnetic field lines.
Q2. An electric motor takes a current of 5A from a 220V supply. Calculate the power and
energy consumed in 2 hours. (CBSE 2012)
A.
Given: I=5A, V=220V, t=2h.
Power, P=VI=220V×5A=1100W=1.1kW.
Energy consumed = Power × Time = 1.1kW×2h=2.2kWh.
Q3. What is the function of an earth wire? (CBSE 2013)
A. The earth wire is a safety device that connects the metallic body of an appliance to the
ground. In case of a fault where the live wire touches the metal casing, the current flows to
the earth, preventing the user from getting an electric shock.
Q4. What is the difference between an AC and DC supply? (CBSE 2014)
A. Direct current (DC) flows in only one direction, while alternating current (AC) periodically
reverses its direction. The frequency of AC is 50 Hz in India.
Q5. What is a solenoid? How does it behave like a magnet? (CBSE 2015)
A. A solenoid is a cylindrical coil of many turns of insulated wire. It behaves like a bar magnet
when a current is passed through it. One end acts as a North pole, and the other acts as a
South pole.
Q6. The magnetic field lines inside a current-carrying solenoid are:
(a) straight
(b) parallel to the axis of the solenoid
(c) straight and parallel to the axis of the solenoid
(d) all of the above (CBSE 2016)
A. (c) straight and parallel to the axis of the solenoid.
Q7. State Fleming's Left-Hand Rule. (CBSE 2017)
A. Fleming's Left-Hand Rule helps to find the direction of force on a current-carrying
conductor in a magnetic field. The thumb, forefinger, and middle finger of the left hand are
stretched perpendicular to each other. The forefinger represents the direction of the
magnetic field, the middle finger represents the direction of the current, and the thumb
represents the direction of the force.
Q8. A magnetic compass shows a deflection when placed near a current-carrying wire. Why?
(CBSE 2018)
A. A current-carrying wire produces a magnetic field around it. The compass needle, being a
small magnet, aligns itself with the external magnetic field, which causes it to show a
deflection.
Q9. Why are household appliances connected in parallel? (CBSE 2019)
A. Household appliances are connected in parallel because this ensures that each appliance
gets the same voltage as the supply line (220 V). Additionally, if one appliance stops working,
the circuit for the other appliances remains complete, so they continue to function.
Q10. What is the role of a fuse in a domestic electric circuit? (CBSE 2011)
A. The fuse is a safety device that protects circuits and appliances from overloading. It has a
high resistance and a low melting point. When an excessive current flows through the circuit,
the fuse wire melts, breaks the circuit, and prevents damage to the appliances.
Q11. An electron enters a magnetic field at right angles to it. What is the direction of the force
on the electron? (CBSE 2012)
A. The direction of the force is perpendicular to both the magnetic field and the direction of
motion of the electron. It can be determined by Fleming's Left-Hand Rule.
Q12. Name two advantages of AC over DC. (CBSE 2015)
A. 1. The voltage of AC can be easily changed using transformers, making it suitable for long-
distance transmission. 2. Power loss during long-distance transmission is significantly less for
AC compared to DC.
Q13. Why is an ammeter always connected in series and a voltmeter in parallel? (CBSE 2018)
A. An ammeter is connected in series because it has very low resistance and needs to
measure the total current flowing through the circuit. A voltmeter is connected in parallel
because it has very high resistance and measures the potential difference across two points
without drawing significant current from the circuit.
Q7. State Fleming's Left-Hand Rule. (CBSE 2017)
A. Fleming's Left-Hand Rule helps to find the direction of force on a current-carrying
conductor in a magnetic field. The thumb, forefinger, and middle finger of the left hand are
stretched perpendicular to each other. The forefinger represents the direction of the
magnetic field, the middle finger represents the direction of the current, and the thumb
represents the direction of the force.
Q8. A magnetic compass shows a deflection when placed near a current-carrying wire. Why?
(CBSE 2018)
A. A current-carrying wire produces a magnetic field around it. The compass needle, being a
small magnet, aligns itself with the external magnetic field, which causes it to show a
deflection.
Q9. Why are household appliances connected in parallel? (CBSE 2019)
A. Household appliances are connected in parallel because this ensures that each appliance
gets the same voltage as the supply line (220 V). Additionally, if one appliance stops working,
the circuit for the other appliances remains complete, so they continue to function.
Q10. What is the role of a fuse in a domestic electric circuit? (CBSE 2011)
A. The fuse is a safety device that protects circuits and appliances from overloading. It has a
high resistance and a low melting point. When an excessive current flows through the circuit,
the fuse wire melts, breaks the circuit, and prevents damage to the appliances.
Q11. An electron enters a magnetic field at right angles to it. What is the direction of the force
on the electron? (CBSE 2012)
A. The direction of the force is perpendicular to both the magnetic field and the direction of
motion of the electron. It can be determined by Fleming's Left-Hand Rule.
Q12. Name two advantages of AC over DC. (CBSE 2015)
A. 1. The voltage of AC can be easily changed using transformers, making it suitable for long-
distance transmission. 2. Power loss during long-distance transmission is significantly less for
AC compared to DC.
Q13. Why is an ammeter always connected in series and a voltmeter in parallel? (CBSE 2018)
A. An ammeter is connected in series because it has very low resistance and needs to
measure the total current flowing through the circuit. A voltmeter is connected in parallel
because it has very high resistance and measures the potential difference across two points
without drawing significant current from the circuit.
Q14. What is the frequency of AC in India? (CBSE 2014)
A. The frequency of alternating current (AC) in India is 50 Hz.
Q15. What happens to the magnetic field of a straight conductor if the current is doubled?
(CBSE 2019)
A. The strength of the magnetic field is directly proportional to the magnitude of the current.
Therefore, if the current is doubled, the magnetic field strength will also be doubled.
A. The frequency of alternating current (AC) in India is 50 Hz.
Q15. What happens to the magnetic field of a straight conductor if the current is doubled?
(CBSE 2019)
A. The strength of the magnetic field is directly proportional to the magnitude of the current.
Therefore, if the current is doubled, the magnetic field strength will also be doubled.
CBSE Class 10 Science: Our Environment
Part 1: Detailed Notes
Eco-system
An eco-system is a self-contained unit of living organisms (biotic components) and their
non-living environment (abiotic components) interacting with each other. It can be natural,
like a forest, a pond, or a grassland, or artificial, such as an aquarium or a garden.
Components of an Eco-system:
1. Biotic Components: All living organisms. They are further divided based on their
nutritional needs.
o Producers: Organisms that produce food using inorganic substances (e.g.,
green plants, algae).
o Consumers: Organisms that depend on producers for food. They can be
herbivores, carnivores, or omnivores.
o Decomposers: Organisms (e.g., bacteria, fungi) that break down dead
remains of plants and animals, returning nutrients to the environment.
2. Abiotic Components: All non-living factors like air, water, soil, sunlight,
temperature, and minerals.
Environmental Problems
Human activities have a significant impact on the environment, leading to several
problems. Two of the most critical issues are ozone depletion and waste management.
Ozone Depletion
The ozone layer is a protective layer in the atmosphere that absorbs harmful ultraviolet
(UV) radiation from the sun, preventing it from reaching the Earth's surface. UV radiation
can cause skin cancer, cataracts, and damage to the immune system.
Cause of Ozone Depletion:
The main cause of ozone depletion is the high concentration of human-made chemicals,
especially chlorofluorocarbons (CFCs), which were widely used in refrigerants, fire
extinguishers, and aerosol sprays. When these chemicals reach the upper atmosphere, UV
radiation breaks them down, releasing chlorine atoms. These chlorine atoms act as
catalysts, breaking down thousands of ozone molecules.
Part 1: Detailed Notes
Eco-system
An eco-system is a self-contained unit of living organisms (biotic components) and their
non-living environment (abiotic components) interacting with each other. It can be natural,
like a forest, a pond, or a grassland, or artificial, such as an aquarium or a garden.
Components of an Eco-system:
1. Biotic Components: All living organisms. They are further divided based on their
nutritional needs.
o Producers: Organisms that produce food using inorganic substances (e.g.,
green plants, algae).
o Consumers: Organisms that depend on producers for food. They can be
herbivores, carnivores, or omnivores.
o Decomposers: Organisms (e.g., bacteria, fungi) that break down dead
remains of plants and animals, returning nutrients to the environment.
2. Abiotic Components: All non-living factors like air, water, soil, sunlight,
temperature, and minerals.
Environmental Problems
Human activities have a significant impact on the environment, leading to several
problems. Two of the most critical issues are ozone depletion and waste management.
Ozone Depletion
The ozone layer is a protective layer in the atmosphere that absorbs harmful ultraviolet
(UV) radiation from the sun, preventing it from reaching the Earth's surface. UV radiation
can cause skin cancer, cataracts, and damage to the immune system.
Cause of Ozone Depletion:
The main cause of ozone depletion is the high concentration of human-made chemicals,
especially chlorofluorocarbons (CFCs), which were widely used in refrigerants, fire
extinguishers, and aerosol sprays. When these chemicals reach the upper atmosphere, UV
radiation breaks them down, releasing chlorine atoms. These chlorine atoms act as
catalysts, breaking down thousands of ozone molecules.
Effects of Ozone Depletion:
• Increased UV radiation on Earth's surface.
• Rise in cases of skin cancer and cataracts.
• Damage to crops and marine life.
Waste Production and Management
Waste is any substance that is discarded after primary use. It can be classified into two
main types based on its ability to decompose.
1. Biodegradable Substances: These are substances that can be broken down
naturally by the action of decomposers (e.g., bacteria and fungi) over time.
o Examples: Vegetable peels, paper, cotton, wood, and cow dung.
2. Non-biodegradable Substances: These are substances that cannot be broken
down by biological processes. They persist in the environment for a very long time,
causing pollution.
o Examples: Plastics, glass, metals, DDT, and certain pesticides.
Solutions for Waste Production (The 3 R's):
The most effective way to manage waste is to reduce its production. The three R's provide a
simple framework:
• Reduce: Use less, for example, by carrying your own cloth bag instead of using a
plastic one.
• Reuse: Use an item again for the same or a different purpose, for example, using
empty glass jars to store kitchen items.
• Recycle: Collect plastic, paper, and glass waste to be processed into new products.
Part 2: Previous Year's Questions (PYQs)
Q1. What are the components of an ecosystem? (CBSE 2011)
A. The two main components of an ecosystem are the biotic components (all living
organisms) and the abiotic components (non-living factors like air, water, soil, etc.).
Q2. Differentiate between biodegradable and non-biodegradable substances. Give one
example of each. (CBSE 2015)
• Increased UV radiation on Earth's surface.
• Rise in cases of skin cancer and cataracts.
• Damage to crops and marine life.
Waste Production and Management
Waste is any substance that is discarded after primary use. It can be classified into two
main types based on its ability to decompose.
1. Biodegradable Substances: These are substances that can be broken down
naturally by the action of decomposers (e.g., bacteria and fungi) over time.
o Examples: Vegetable peels, paper, cotton, wood, and cow dung.
2. Non-biodegradable Substances: These are substances that cannot be broken
down by biological processes. They persist in the environment for a very long time,
causing pollution.
o Examples: Plastics, glass, metals, DDT, and certain pesticides.
Solutions for Waste Production (The 3 R's):
The most effective way to manage waste is to reduce its production. The three R's provide a
simple framework:
• Reduce: Use less, for example, by carrying your own cloth bag instead of using a
plastic one.
• Reuse: Use an item again for the same or a different purpose, for example, using
empty glass jars to store kitchen items.
• Recycle: Collect plastic, paper, and glass waste to be processed into new products.
Part 2: Previous Year's Questions (PYQs)
Q1. What are the components of an ecosystem? (CBSE 2011)
A. The two main components of an ecosystem are the biotic components (all living
organisms) and the abiotic components (non-living factors like air, water, soil, etc.).
Q2. Differentiate between biodegradable and non-biodegradable substances. Give one
example of each. (CBSE 2015)
A. Biodegradable substances can be broken down by decomposers (e.g., vegetable peels),
while non-biodegradable substances cannot be broken down naturally (e.g., plastic).
Q3. What is the function of the ozone layer? Name a chemical that causes its depletion.
(CBSE 2017)
A. The ozone layer protects the Earth from harmful ultraviolet (UV) radiation from the sun.
The chemical responsible for its depletion is chlorofluorocarbons (CFCs).
Q4. Why are some substances biodegradable and some non-biodegradable? (CBSE 2016)
A. Substances are biodegradable if they can be acted upon by decomposers (bacteria,
fungi) and their enzymes. Non-biodegradable substances cannot be broken down by these
organisms and therefore persist in the environment.
Q5. Why is the use of plastics harmful for our environment? (CBSE 2018)
A. Plastics are non-biodegradable and persist in the environment for a long time. They can
clog drains, harm wildlife that ingest them, and contribute to soil and water pollution.
Q6. What is the role of decomposers in an ecosystem? (CBSE 2019)
A. Decomposers break down the complex organic matter from dead organisms into simpler
inorganic substances. This process returns essential nutrients to the soil, which can be
reused by the producers, thus completing the nutrient cycle.
Q7. List two environmental problems caused by human activities. (CBSE 2015)
A. Two major environmental problems are ozone layer depletion and the accumulation of
plastic waste in landfills and oceans.
Q8. What is a food chain? Give an example. (CBSE 2014)
A. A food chain is a sequence of organisms in an ecosystem through which energy is
transferred from one trophic level to another.
Example: Grass → Deer → Lion
Q9. Why do we need to manage our waste effectively? (CBSE 2016)
A. Effective waste management is crucial to prevent the accumulation of waste, which can
lead to environmental pollution, spread of diseases, and harm to living organisms. It also
helps in conserving natural resources by reusing and recycling materials.
Q10. What would happen if all the decomposers were removed from the ecosystem?
(CBSE 2019)
while non-biodegradable substances cannot be broken down naturally (e.g., plastic).
Q3. What is the function of the ozone layer? Name a chemical that causes its depletion.
(CBSE 2017)
A. The ozone layer protects the Earth from harmful ultraviolet (UV) radiation from the sun.
The chemical responsible for its depletion is chlorofluorocarbons (CFCs).
Q4. Why are some substances biodegradable and some non-biodegradable? (CBSE 2016)
A. Substances are biodegradable if they can be acted upon by decomposers (bacteria,
fungi) and their enzymes. Non-biodegradable substances cannot be broken down by these
organisms and therefore persist in the environment.
Q5. Why is the use of plastics harmful for our environment? (CBSE 2018)
A. Plastics are non-biodegradable and persist in the environment for a long time. They can
clog drains, harm wildlife that ingest them, and contribute to soil and water pollution.
Q6. What is the role of decomposers in an ecosystem? (CBSE 2019)
A. Decomposers break down the complex organic matter from dead organisms into simpler
inorganic substances. This process returns essential nutrients to the soil, which can be
reused by the producers, thus completing the nutrient cycle.
Q7. List two environmental problems caused by human activities. (CBSE 2015)
A. Two major environmental problems are ozone layer depletion and the accumulation of
plastic waste in landfills and oceans.
Q8. What is a food chain? Give an example. (CBSE 2014)
A. A food chain is a sequence of organisms in an ecosystem through which energy is
transferred from one trophic level to another.
Example: Grass → Deer → Lion
Q9. Why do we need to manage our waste effectively? (CBSE 2016)
A. Effective waste management is crucial to prevent the accumulation of waste, which can
lead to environmental pollution, spread of diseases, and harm to living organisms. It also
helps in conserving natural resources by reusing and recycling materials.
Q10. What would happen if all the decomposers were removed from the ecosystem?
(CBSE 2019)
A. If all decomposers were removed, the recycling of nutrients would stop. The dead bodies
of plants and animals would accumulate, and the supply of inorganic nutrients for
producers would be cut off, eventually leading to the collapse of the ecosystem.
Q11. Give one example of an artificial ecosystem. (CBSE 2011)
A. An aquarium is a good example of an artificial ecosystem.
Q12. What are the harmful effects of UV radiation? (CBSE 2018)
A. UV radiation can cause skin cancer, damage to the eyes (cataracts), and weaken the
human immune system.
Q13. Suggest any two methods to reduce the amount of waste. (CBSE 2017)
A. Two methods to reduce waste are:
1. Reduce: Use less, for example, by buying products with minimal packaging.
2. Reuse: Use items more than once, for example, using a glass bottle for water
instead of a plastic one.
Q14. In a food chain, if 1000J of energy is available at the producer level, how much energy
will be available to the secondary consumer? (CBSE 2016)
A. According to the 10% law of energy transfer, only 10% of the energy is transferred to the
next trophic level.
Energy at producer level: 1000J.
Energy at primary consumer level: 10% of 1000J=100J.
Energy at secondary consumer level: 10% of 100J=10J.
Q15. What is the biological name of the "ozone hole"? What is its significance? (CBSE
2012)
A. The "ozone hole" is not a hole but a region of severely depleted ozone concentration in
the stratosphere. Its significance is that it allows harmful UV radiation to penetrate the
atmosphere, posing a threat to all life on Earth.
of plants and animals would accumulate, and the supply of inorganic nutrients for
producers would be cut off, eventually leading to the collapse of the ecosystem.
Q11. Give one example of an artificial ecosystem. (CBSE 2011)
A. An aquarium is a good example of an artificial ecosystem.
Q12. What are the harmful effects of UV radiation? (CBSE 2018)
A. UV radiation can cause skin cancer, damage to the eyes (cataracts), and weaken the
human immune system.
Q13. Suggest any two methods to reduce the amount of waste. (CBSE 2017)
A. Two methods to reduce waste are:
1. Reduce: Use less, for example, by buying products with minimal packaging.
2. Reuse: Use items more than once, for example, using a glass bottle for water
instead of a plastic one.
Q14. In a food chain, if 1000J of energy is available at the producer level, how much energy
will be available to the secondary consumer? (CBSE 2016)
A. According to the 10% law of energy transfer, only 10% of the energy is transferred to the
next trophic level.
Energy at producer level: 1000J.
Energy at primary consumer level: 10% of 1000J=100J.
Energy at secondary consumer level: 10% of 100J=10J.
Q15. What is the biological name of the "ozone hole"? What is its significance? (CBSE
2012)
A. The "ozone hole" is not a hole but a region of severely depleted ozone concentration in
the stratosphere. Its significance is that it allows harmful UV radiation to penetrate the
atmosphere, posing a threat to all life on Earth.
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