Question

The diagram shows the path of a ray of light through a rectangular glass block placed in a liquid of uniform density.

(i) (a) Does the light speed up or slow down in glass, (b) Give reason for your answer. 

(ii) What is the angular, deviation of the emergent ray from the glass block with respect to the incident ray? 

(iii) Show with the help of a ray diagram the path of the ray when incident ray normally falls on the first surface of the glass block and passes through the block and the liquid. 

(iv) What should be the rate of the speed of light through the liquid to the speed through glass so that there is no refraction of light at the boundaries of the glass block when the system is illuminated by light of one colour?

Answer 1

Since the refractive index in glass is usually higher than that of liquid, hence the speed of light in glass will be less. 

(ii) As shown by line in the diagram, the emergent ray is parallel to the incident ray (when produced) and so there is no angular deviation. 

(iii) See the diagram. 

(iv) Since there is no refraction of light at the boundaries of the glass block, it is possible only when the speed of light through the liquid as well as through the block is the same. Hence the ratio between the speed of light through the liquid to the speed of light through glass must be 1 (one).