Refraction and Dispersion of light.pptx

HELLO EVERYONE MY NAME IS DAKSH GUPTA I READ IN CLASS 8 THIS PRESENTATION WILL HELP YOU TO MAKE YOUR OWN PRESENTATION BETTER THAN ME THANK YOU FOR SEEING THIS PRESENTATION

1. REFRACTION AND DISPERSION OF LIGHT 

2. WHAT DO YOU understand the refraction of light ? This bending by refraction makes it possible for us to have lenses, magnifying glasses, prisms and rainbows. Even our eyes depend upon this bending of light. Without refraction, we wouldn't be able to focus light onto our retina .

3. Components

4. REFRACTION OF LIGHT  When a ray of light enters from one medium to another, then it deviates from its actual path. This phenomenon is called refraction of light.

5. Refraction and the speed of light  Light travels at lower speeds in glass and water than in air . We say that glass and  water are optically denser than air . Optical density  : Optical density is a property of a transparent material. It is a measure of the speed of light through the material. 

6. when a ray of light travels from a rarer medium to a denser medium, then  it bends towards the normal  and when the light travels from a denser medium to a rarer medium, it bends away from the normal.  

7. when a ray of light travels from a rarer medium to a denser medium, then  it bends towards the normal  and when the light travels from a denser medium to a rarer medium, it bends away from the normal.

8. Effects of refraction  Real and apparent depth : The real depth is the actual depth of the bottom of the tank and the apparent depth is the virtual depth that is observed as a result of the refraction of light . The apparent depth depends upon the refractive index of the medium. 

9. Apparent bending of a pencil Rays of light from the tip  of the pencil bend away from the normal as they go from water to air. The refracted appear to come from point . Thus the immersed portion of a pencil in water appears . Hence, the pencil appears to bent at the water surface. Moreover, the immersed portion of the pencil in water also appears to be shorter than the actual length of the pencil.

10. Refraction through the Glass Slab Since the angle of incidence is equal to the angle of emergence, therefore the emergent ray is parallel to the incident ray. In the glass slab,  the light ray gets refracted two times firstly, from rarer to denser medium and secondly from denser to rarer medium

11. refraction through a prism Refraction is  the bending of light when it goes from one medium to another  so, when a ray of light passes through a glass prism, refraction of light occurs both, when it enters the prism as well as when it leaves the prism. 

12. dispersion When white light is passed through a glass prism it splits into its spectrum of colours (in order violet, indigo, blue, green, yellow, orange and red) and this  process of white light splitting into its constituent colours  is termed as dispersion.

13. reason for dispersion of light Cause of Dispersion: When white light passes through a glass prism, its constituent colours (red, orange, yellow, green, blue, indigo, violet) travel with different speeds in the prism because refractive index is color dependent. This causes the dispersion of light.

14. LENSES  A transparent medium bounded by two surfaces of which at least one is spherical is called a lens.

15. LENSES are classified into two types : Concave lens : A concave lens is thinner in the middle and thicker at the edges. It is also known as Converging Lens   Convex lens :  A convex lens is thicker in the middle and thinner at the edges. as It is also known as Diverging Lens

16. Principal axis. :  An imaginary line passing through the centers of two spheres of which the spherical lens is a part is known as the principal axis terms related to lenses

17. Optical Centre: The point on a lens through which a ray of light passes without deviation  is called the optical centre   of the lens.  terms related to lenses

18.  Principal Focus: The point on a lens through which a ray of light passes without deviation is called the optical centre   of the lens.   terms related to lenses

19. Focus length : The distance between the focus and the optical center  is known as focal length. It is denoted by f. terms related to lenses

20. Image formed by a lens

21. The image formed by a convex lens varies in size, position and nature (erect or inverted , real or virtual ) depending upon the distance of the object from the lens . Image formed by a convex lens 

22. When an object is at infinity , then  the rays coming from it is almost parallel to principal axis . Hence the image formed is  at focus.  The image of a very far off object (object at infinity) is  a real, diminished and almost point-like image .  Object very far off ( or at infinity):

23. When an object is placed beyond 2f in front of a convex lens , then the image formed is between f and 2f on the other side of the lens , it is  real , inverted and smaller than the object  . It can be formed on a screen placed at that point . Object beyond 2f :

24. When an object is placed at 2f in front of a convex lens, the image is real, inverted and and of the same size the object    Object at 2f :

25. When an object is placed between F and 2F  in front of a convex lens , The image is real , inverted  and larger than the object . It is situated beyond 2f on the other side of the lens  Object between f and  2f

26. When an object is placed at 2f in front of a convex lens, The image is real , inverted  and inverted . It is highly enlarged in size than the object . The image is formed at infinity . Object at f 

27. When an object is placed between F and 0 in front of a convex lens,  then  its image is formed between C1 and F1 . The image is enlarged, erect and virtual. Object between F AND 0

28. A diverging lens always forms a virtual image , which is erect and smaller in size than the object . It is formed between the optical centre and the focus, on the same side of the lens as the object . The image formed by a concave lens

29. Eye – the natural optical instrument  Light entering the human eye is first refracted by the cornea. The refracted light is then incident on an iris. The lens is just behind the iris and light after refracted through the pupil falls on it and forms a sharp image. Image formation exactly on the retina enables us to see the object real and inverted.

30. Functions of human eye ( the natural optical instrument ) Cornea : The eye consists of the eyeball which is nearly spherical in shape . It in front portion , It is called cornea . The light enters the eye through the cornea  Iris  The colored tissue at the front of the eye that contains the pupil in the center . The iris helps control the size of the pupil to let more or less light into the eye. Pupil   The pupil is the opening at the center of the iris through which light passes. The iris adjusts the size of the pupil to  control the amount of light that enters the eye . Aqueous  The aqueous humour is  a thin, transparent fluid similar to plasma . It's made up of 99.9% water – the other 0.1% consists of sugars, vitamins, proteins and other nutrients. This fluid nourishes the cornea and the lens, and gives the eye its shape

31. Lens  The image formed by the eye lens on the retina is  real, inverted, diminished . Retina  The image formed at the retina of the human eye is  real and inverted . It is due to the presence of a convex lens in the eye. Ciliary muscles  The ciliary body is a circular structure that is an extension of the iris, the colored part of the eye. The ciliary body produces the fluid in the eye called aqueous humor. It also contains the ciliary muscle, which  changes the shape of the lens when your eyes focus on a near  objec Vitreous  humour   The vitreous humor's main role is to  maintain the round shape of the eye . The size and shape of the vitreous humor also ensures that it remains attached to the retina, which is the layer at the back of the eye that is sensitive to light Cone  cones are sensitive to bright light,  can detect  colour  .  We have three types of cones: blue, green, and red.  Rods  They are sensitive to light levels and help give us good vision in low light. They are concentrated in the outer areas of the retina and give us peripheral vision.

32. Blind spot – the area of no vision  At the junction of the optic nerve and the retina,  there are no sensory cells that could produce impulses when light falls on that location , so no vision is possible at that spot. This is called the blind spot.

33. Accommodation of the eye  The capacity of the eye lens to adapt its focal length throughout the order to clearly concentrate rays from a distant and a close object here on the retina  is called the eye's accommodating power. Human eye lenses are translucent and crystalline. The least distance at which the ye can see an object clearly is called the near point of the ye . The far point of the eye is the maximum distance at which it can see clearly. For a normal eye the near point is about 25 cm and the far point of the eye is  at infinity . A normal eye can see objects clearly that are between 25 cm and infinity.

34. Accommodation of the eye 

35. Defects of vision  There are two main defects the eye suffers from  These are : Myopia  Hypermetropia 

36. Defects of vision  Myopia  :  Myopia is  an eye defect or common abnormality of the eye in which the near vision is clear while distant vision is blurred . This condition is known as myopia also it is called near or short-sightedness. Retina is that part of the eye which provides a surface for image formation. 

37. Defects of vision  The far point of a myopic person is  80 cm in front of the eye .

38. Defects of vision  Defect corrected by concave lens .

39. Defects of vision  Hypermetropia or long sightedness . Hypermetropia is also known as  far-sightedness . A person with hypermetropia can see distant objects clearly but cannot see nearby objects distinctly. The near point, for the person, is farther away from the normal near point (25 cm)

40. Defects of vision  Near point of hypermetropic eye  For a person suffering from hypermetropia , the near point is beyond 25 cm 

41. Defects of vision  Defect corrected by convex lens . Hypermetropia is corrected using a convex lens of appropriate power.  The convex lens converges the light rays so that the final image from human eye lens is formed on the retina . 

42. Defects of vision  Cataract :  The medical condition in which the lens of eye of a person becomes progressively cloudy resulting in blurred vision  is called cataract. Cataract develops when the eye-lens of a person becomes cloudy (or even opaque) due to the formation of a membrane over it.

43. Care of the eyes We must take proper care of the eyes . We must  try to avoid any kind of injury to our eyes . Some simple precautions given below may help in protecting our eyes . Do not work or read in a dim light or very bright light. This tires the eyes  wash our eyes regularly with cold water We must get eyesight checkups done in case of any changes in the vision. We must avoid watching screens for a very long period of time. Etc.

44. Persistence of vision  Even after the object is removed, the impression of an object seen by the eye remains on the retina for 1/16th of a second . If we see another object before this time, the impressions of the two merge to give us a sense of continuity. This eye property is known as persistence of vision.

45. Visually impairment is  the decrease in the ability of a person's sight to a large degree such that it cannot be fixed by any conventional means of corrections like glasses and lenses . The term blind people or blindness refers to a complete or nearly complete vision loss. The visually impaired

46. Use braille  Braille is a system developed by Louis Braille in 1824 to help visually challenged people . It is a code by which languages such as English, French, Spanish, etc can be written and read. This code consists of raised dots, that can be read with fingers by blind people. The visually impaired

47.  braille  code

48. Made by – Daksh gupta