Science
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Chapter 10: Reflection and Refraction
Class: X
Exercises 3
Question 1
A ray of light travelling in air enters obliquely into water. Does the light ray bend towards the normal or away from the normal? Why?
Answer 1
Yes, A ray of light travelling in air enters obliquely into water bends towards the normal. A light ray bends towards the normal when it travels from an optically rarer to denser medium. As water is optically denser than air and therefore a ray of light travelling from air into the water will bend towards the normal.
Question 2
Light enters from air to glass having refractive index 1.50. What is the speed of light in
the glass? The speed of light in vacuum is 3 × 108 m s−1.
Answer 2
Question 3
Find out, from table below, the medium having highest optical density. Also find the
medium with lowest optical density.
Answer 3
Optical density is directly proportional to the refractive index of that medium. That means a medium which has the highest refractive index will have the highest optical density. It can be observed from the given table that diamond has the highest refractive index (2.42) and hence it had highest optical density.
Air has the lowest refractive index (1.0003) and therefore, air has the lowest optical density.
Question 4
You are given kerosene, turpentine and water. In which of these does the light travel fastest? Use the information given in the below table.
Answer 4
The velocity of the light in the medium is indirectly proportional to the refractive index of that medium. That means light will travel faster in the medium which has the lowest refractive index. It can be observed from the given table that refractive index of kerosene is 1.44, turpentine is 1.47, and water is 1.33. Water has the lowest refractive index and the light will travel faster in the water as compared to kerosene and turpentine.
Question 5
The refractive index of diamond is 2.42. What is the meaning of this statement?
Answer 5
The refractive index of diamond is 2.42. That means that the speed of light in diamond
will reduce by a factor 2.42 compared to the speed of light in air.
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