# Physics Questions and Answers – Ray Optics – Refraction

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This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Ray Optics – Refraction”.

1. Identify the factor on which the angle of deviation of the prism does not depend.
a) The angle of incidence
b) The material of the prism
c) The angle of reflection
d) The wavelength of light used

Explanation: Factors on which the angle of deviation depends are ➔ the angle of incidence, the material of the prism, the wavelength of light used, and the angle of the prism. So, the factor on which the angle of deviation that does not depend on is the angle of reflection.

2. Calculate the refractive index of the material of an equilateral prism for which the angle of minimum deviation is 60°.
a) $$\frac {\sqrt {3}}{2}$$
b) √3
c) $$\frac {1}{2}$$
d) $$\frac {1}{\sqrt {2}}$$

Explanation: Refractive index of the prism material is μ = $$\frac { \{ sin \frac {(A+\delta_m)}{2} \} }{ \{ sin \frac {A}{2} \} }$$
μ = $$\frac { \{ sin \frac {(60^o+60^o)}{2} \} }{ \{ sin \frac {60^o}{2} \} }$$
μ = √3.

3. Which of the following causes dispersion?
a) Refraction
b) Reflection
c) Total internal reflection
d) Total internal dispersion

Explanation: The reason is that for a given angle f incidence, the reflection is the same for all the wavelengths of white light while the angle of refraction is different for different wavelengths. Therefore, this is how dispersion is caused.

4. What happens to the frequency and the wavelength when light passes from a rarer to a denser medium?
a) Wavelength remains unchanged but frequency changes
b) They are independent
c) Wavelength and frequency changes
d) Wavelength changes but the frequency remain unchanged

Explanation: When light passes from a rarer to a denser medium, the wavelength of light changes but the frequency remains unchanged. Therefore, there is no change in the frequency of light, only the wavelength changes.

5. What is the relative refractive index of water with respect to glass?
a) Unity
b) More than unity
c) Less than unity
d) Zero

Explanation: Absolute refractive index = $$\frac {Speed \, of \, light \, in \, vacuum}{Speed \, of \, light \, in \, the \, medium}$$. The relative refractive index of water with respect to glass is less than unity.

6. The refraction in a water tank makes apparent depth the same throughout.
a) True
b) False

Explanation: No, this statement is false. Apparent depth is maximum for that part of the bottom of the tank which is observed normally. Apparent depth decreases with increasing obliquity. Therefore, the refraction in a water tank does not make apparent depth the same throughout.

7. What will be the color of the sky in the absence of the atmosphere?
a) White
b) Dark
c) Blue
d) Pink

Explanation: The sunlight will not be scattered in the absence of the atmosphere. So the sky will appear dark. So, the sky will no longer be blue in the absence of an atmosphere.

8. On what factor does the normal shift through a refracting medium depend?
a) The thickness of the refracting medium
b) Angle of Prism
c) Angle of deviation
d) Convection

Explanation: The normal shift depends on the thickness of the refracting medium and the refractive index of the material. The normal shift does not depend on the angle of the prism, angle of deviation, and convection.

9. A lens immersed in a transparent liquid is not visible. Under what condition can this happen?
a) Less refractive index
b) Higher refractive index
c) Same refractive index
d) Total internal reflection is zero

Explanation: When the refractive index of the liquid is the same as the lens material, no light will be reflected by the lens and hence it will not be visible. So, the lens immersed in a transparent liquid will not be visible.

10. What is the cause of the blue color of the ocean?
a) Reflection
b) Scattering of light by water molecules
c) Total internal reflection
d) Refraction 