The change in the direction of the light wave caused by its change in speed when it passes from one medium to another is known as the refraction of light. Formation of the rainbow, mirage, looming, twinkling of stars etc., are some real-life examples of refraction. When a light ray travels at an angle into a medium of a different refractive index, it refracts. Due to this change in speed of the light, its direction also changes and thus, refraction occurs.
The refraction index, also termed the refractive index, defines how fast light travels through the material. The refractive index is a dimensionless quantity.
For a given material, the ratio between the speed of light in a vacuum (c) and the speed of light in the medium (v) is known as the refractive index.
Suppose the refractive index for a medium is denoted by n. In that case, it is given by the following formula:
n = c/v
The below videos help to revise the chapter Light Reflection and Refraction Class 10
Important Questions on Refraction
1) The angle of deviation of the prism does not depend upon which of the following factors?
a) Angle of incidence
b) Material of the prism
c) Angle of reflection
d) Wavelength of light used
Correct Option: (c)
Explanation: The angle of incidence, the material of the prism, wavelength of light, and the angle of the prism are the factors on which the angle of deviation depends. But the angle of deviation has nothing to do with the angle of reflection.
2) Which of the following phenomena are the main causes of dispersion?
a) Reflection
b) Refraction
c) Interference
d) Diffraction
Correct Option: (b)
Explanation: The dispersion depends on refraction because the angle of refraction differs for different wavelengths of white light, while the angle of reflection is the same for all the wavelengths of white light.
3) When a light ray travels from a rarer medium to a denser medium, what will happen to its frequency and wavelength?
a) Frequency changes, but wavelength remains unchanged
b) Both are independent
c) Frequency and wavelength will change together
d) Frequency remains unchanged, but the wavelength changes
Correct Option: (d)
Explanation: There will be no change in the frequency of light because when light passes from a rarer to a denser medium, the wavelength of light fluctuates, but the frequency remains unaffected.
4) The relative refractive index of water with respect to glass will be _______.
a) Zero
b) Unity
c) Cannot be determined
d) Less than unity
Correct Option: (d)
Explanation: The relative refractive index of water with respect to glass, according to the formula of absolute refractive index (Speed of light in vacuum/Speed of light in the medium), is less than unity.
5) The wavelength and refractive index are directly proportional to each other. Is it true or false?
a) True
b) False
Correct Option: (b)
Explanation: Since the wavelength and refractive index are inversely proportional, this statement is false.
6) The apparent depth of a water tank is the same throughout because of refraction.
a) True
b) False
Correct Option: (b)
Explanation: The above statement is false because the apparent depth of the tank is maximum for that part that is observed normally.
7) In the absence of the atmosphere, what will be the colour of the sky?
a) Pink
b) Dark
c) Yellow
d) Red
Correct Option: (b)
Explanation: The sky will appear dark because, in the absence of the atmosphere, the sunlight will not be scattered. So, the sky will no longer be blue in the absence of an atmosphere.
8) The normal shift through a refracting medium depends upon which of the following factors?
a) Convection
b) Angle of incidence
c) Angle of reflection
d) The thickness of the refracting medium
Correct Option: (d)
Explanation: The normal shift depends on the refractive index of the material and the thickness of the refracting medium.
9) Name the phenomenon in which a lens seems to be invisible when immersed in a transparent liquid.
a) Less refractive index water
b) Higher refractive index or lens
c) Due to the same refractive index or lens and water.
d) None of these
Correct Option: (c)
Explanation: No light will be reflected by the lens when the refractive index of the liquid and lens material is the same, and hence, it will not be visible. So, a lens seems to be invisible when immersed in a transparent liquid.
10) What is the reason for the blue colour of the ocean?
a) Total internal reflection
b) Refraction
c) Interference
d) Scattering of light by water molecules
Correct Option: (d)
Explanation: Due to the superior scattering of light by water molecules, the ocean appears to be blue. This is the fundamental reason for many other phenomena, like the sky appearing to be blue or reddish at sunrise or sunset.
Related Videos
Revision: Optical Phenomena Class 10
Revision: Chapter Human Eye and the Colourful World
Practice Questions
1) What is refraction?
2) Define Snell’s law.
3) What is reflection?
4) Explain total internal reflection.
5) What are the laws of refraction?
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