Exercise 4-A

Q.8. State the Snell’s law of Refraction of light.
Ans. The Snell’s Laws of refraction of light are :
(i) The incident ray, the refracted ray and the normal at the point of incidence, all lie in the same plane.
(ii) The ratio of the sine of the angle of incidence i to the sine of angle of refraction r is constant for the pair of given media. Mathematically :

The constant is called refractive index of the second medium with respect to the first medium.

Q.10. How is the refractive index of a medium related to the speed of light in it?
Ans. The refractive index of a medium is defined as the ratio of the speed of light in vacuum(or air) to the speed of light in that medium. The speed of light of all colours is same in air or vacuum, but in other transparent medium, the speed of light is different for different colours.

Q.13. What do you understand by the statement ‘the refractive index of glass is 1.5 for white light’ ?
Ans. This means the speed of white light in air or vacuum is 1.5 times more than in glass.

Q.17. Name two factors on which the refractive index of a medium depends? State how does it depend on the factors stated by you.
(in the below answer we are explaining three factors. you can write any two.)
Ans. The refractive index of a medium depends on three factors :
– Nature of the medium : If the speed of light in a medium is lesser as compared in air or vacuum, means the refractive index of that medium is high.
– Physical condition such as temperature : If temperature of the medium increases the speed of light increases so refractive index decreases.
– The color or wavelength of light : The speed of light of all colours are same in air or vacuum, but in any other medium the speed of light is different for different colours. So refractive index is different for different colours.

Q.23. What is lateral displacement? Draw a ray diagram showing the lateral displacement of a ray of light when it passes through a parallel sided glass slab.
Ans. The perpendicular distance between the direction of the incident ray and emergent ray is called lateral displacement.

In figure we observe that due to refraction of light at two parallel surfaces of a parallel sided glass block, the incident ray and the emergent ray are not along same line but parallel to each other. The perpendicular distance “d” between the path of emergent ray and direction of incident ray is called the lateral displacement.

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