Refraction

When light travelling in one medium falls on the surface of second medium the following three effect may occur.
1:- A part of incident light is reflected back into the same medium. This is called Reflection of light.
2:- A part of light is passes through the medium.This Is known as Refraction of light.
3:- And remaining part of the light is absorbed by the surface on which the light fall. This is known as Absorption of light.

1. REFRACTION A STEP TOWARDS VISION

2. CONTENT Nature of light. Introduction. Basic law of refraction. Snell’s law of refraction. Refraction through Glass slab. Causes of refraction. Refraction through glass prism. Terminology. Angle of deviation Vs angle of incidence. Refraction by curved surface. Refraction by spherical lenses.

3. Refraction by spherical lenses. Refraction by convex lens. Refraction by concave lens. Refraction by cylindrical lens. Spherical lens versus cylindrical lens . Refraction and the Eyes. Refraction for distance and near vision. Refraction caused by eye lens.

4. Nature of light Rectilinear propagations of light. When light travelling in one medium falls on the surface of second medium the following three effect may occur. 1:- A part of incident light is reflected back into the same medium. This is called Reflection of light. 2:- A part of light is passes through the medium. This Is known as Refraction of light . 3:- And remaining part of the light is absorbed by the surface on which the light fall. This is known as Absorption of light.

5. INTRODUCTION Definition -The phenomenon of the bending of light as it passes obliquely from one transparent medium to another due to change in density of medium and speed of light. The path along which the travel in the first medium is called INCEDENT RAY . And that in the second medium is called REFRACTED RAY. The angle which the incident ray and the refracted ray makes with the normal at the surface of separation are called “angle of incidence” and “angle of refraction”

6. law of refraction First law:- The incident ray, Refracted ray and the normal to the surface at the point of incidence all lie in the same plane. Second law:- The ratio of the angle of incidence to that of the angle of refraction is constant for a given pair of media This law is also known as snell’s law of refraction.

7. Snell’s Descartes law Discovered by Willobrord Snellius in1621. It is used to describe the relation between angle “i” and angle “r” when light passing through a boundary b/w two different isotropic media such as Glass or Air. In experimental optics it is used to find the refractive index of material. RELATION :-

8. REFRACTION THROUGH GLASS SLAB Whenever a refraction occur through glass slab three phenomenon will be occur 1:- When a ray passes from optically rarer to denser medium it bends towards the normal i.e angle “i” greater than angle “r” . 2:-When a ray passes from optically denser to rarer medium it bends away from the normal i.e angle “r” greater than angle “i” . 3:- A ray of light travelling along the normal passes undeflected i.e- angle “i” is equal to angle “r”

9. GLASSSLAB 1:-When parallel light ray fall obliquely upon a glass plate (with parallel side) there direction is changed on account of the retardation of one edge of the beam before the other. 2:-When entire width of beam has entered the substance of the glass, all the ray will be equal retarded throughout ,and consequently travelling at a uniform through lessened speed .

10. CAUSE OF REFRACTION OF LIGHT The amount by which the beam of light is bent depend on three factors these are as follows, 1:- Optical density- The bending of light is dependent on the retardation of light the more resistance the body offers the more slowly will be light be made to travel. 2:- Refractive index - It is the relation b/w angle of incidence and angle of refraction. Because of this relation the more oblique the light ray the greater will be the bending. 3:- Wavelength - Blue light is more bent than red light because of difference in wavelength.

11. Refraction through prism A prism is a transparent optical element with flat, polished surface that refract light. When a light ray fall on a non parallel surface (PRISM) the direction of light also change. The incident beam of light is retarded and bent round and run through the substance of the glass until reaches the another surface . Consequently the beam is bent round further in the same sense and is deviated out of its original path altogether . since a ray on entering the denser medium (GLASS) from a rare one (AIR) , the incident ray bends towards the base as it enter the PRISM .

12. Light after passing through a prism travels on in a parallel beam ,it is never brought to a Focus and no image is formed . But in the prism the light source should be shifted to apex when seen from the base of another side.

13. terminology 1:- Angle of incidence- The angle b/w the incidence ray and the normal. 2:- Angle of refraction- The angle b/w the refracted ray and the normal. 3:- Angle of deviation- The angle b/w the incidence ray and the emergent ray. 4:- Angle of minimum deviation- The minimum value of the angle of deviation suffered by a ray on passing through a prism . The main phenomenon of the prism is to deviate the white light into seven colors which can be appear as spectrum on screen. In prism dispersion occur because refractive index of material varies with the wavelength or color of light used

14. Angle of deviation versus angle of incidence The given fig shows the variation of angle of deviation with the angle of incidence “i”. For a given prism and for a given pair of light , the angle of deviation depends upon the angle i only i.e.- As angle “i” increases , the angle of deviation first decreases and reduce a min value of deviation and then decreases .

15. Refraction by a curved surface When parallel rays of light strike a spherical surface ,each individual ray will be bent to a different degree and the rays may then all meet at a focus. The distance of this focus from the surface depend on the curvature and the optical density of the two media .

16. REFRACTION BY spherical Lenses Refraction in spherical lenses occur because in these lenses all the meridian have same curvature , so the ray coming from infinity should be focus at a point. When the parallel light is passes through the lens ,the light ray is converge or diverge because of prismatic effect in lenses. As shown in given figures:-

17. Refraction by convex lens When light ray go through a CONVEX IENS the light ray are refracted and show convergence and all the ray meet at a point on a principal axis known as FOCUS and form real and inverted image. For any ray entering the lens that is not along a normal the light will change direction because here change in media occurs i.e. light ray travel from Rarer-Denser-Rarer. A ray entering along the normal passes straight without any deviation because lens can also act as parallel plate glass slab.

18. Refraction by concave lens The basic difference b/w the refraction of convex and concave is the nature of lens.i.e convex les is of converging nature whereas concave lens is of diverging nature so all the parallel beam of light passes through the concave lens are diverging so these rays never meet at focus actually but appear to meet at focus and form virtual and erect image of object. In this phenomenon refraction also occurs due to change in media i.e. Rarer-denser-rarer.

19. Refraction by cylindrical lens 1:- A cylindrical lens is a piece of glass , one of the surface of which is cylindrical . 2:- A cylindrical lens is a lens which focuses light into a line instead of a point . 3:- This lens compresses the image in the direction perpendicular to the image line. 4:- A Cylindrical lens has two meridians.i.e one is plane meridian having no power and plane perpendicular to plane meridian is known as power meridian. 5:- This lens is used to correct astigmatism.

20. Spherical lens versus cylindrical l ens SPHERICAL LENS 1 :- Spherical lens are used to correct distance.(Myopia and hypermetropia). 2:-Spherical lens have same power in all meridian . 3:- it can focus the light into the point image . 4:-Spherical lens is curved both vertically and horizontally. 5:-Spherical lens is the best for distortion free vision due to its shape. CYLINDRICAL LENS 1:- this lens is used to correct astigmatism. 2:-This lens have different power in different meridians. 3:-This lens cannot form the point image but focus the light as line parallel to cylindrical axis. 4:- This lens is flat vertically and curved horizontally across face. 5:-Cylindrical lens are flat at the edge , which can cause distortion at certain angles.

21. Refraction and the eyes 1:- Refraction is the phenomenon which makes the image formation possible by eyes. 2:-Most of the refraction in the eyes takes place at first anterior most surface of the eye i.e. CORNEA. 3:- Since the refraction through cornea takes place because large change in the Refractive index which the light experiences. 4:- About 80% of the refraction occur through cornea while rest of 20% refraction occur through crystalline lens. 5:- The image formed at retina is inverted but our brain convert into erect image.

22. Distance vision and near vision In distance vision light rays from distance object are parallel ,so no much refraction occurs in this case In close vision light rays that are coming from closer object are diverges and need much refraction to focus properly .

23. In our eyes there are total six elements through refraction occurs these are:- anterior surface of cornea, the substance of cornea, the posterior surface of cornea, the aqueous humour, the anterior surface of lens, the posterior surface of lens, the substance of lens and vitreous humour. But the refraction at the posterior surface of cornea is ignored because the R.I. is same as that of aqueous humour. The light entering the eyes is refracted at the anterior surface of cornea because of the two reason- 1:- curvature of cornea. 2:- Difference in R.I. of air and cornea.

24. Refraction caused by Eye lens 1:-Since lens is made of several layer so central nucleus have higher R.I. than the cortical layer. 2:- The curvature of the outer layer of lens is less than that of the inner ,so the central nucleus is more spherical than the cortical layer . so refraction is greater at the central region of the lens than the cortical region . 3:-The comparatively greater refractive strength of the central region of lens has a biological significance. A:- It reduces the amount of scattered light within the eyeball. B:- It reduces the spherical and chromatic aberration .