CBSE Class 12 · 2023 · Wave OpticsMultiple Choice

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A ray of monochromatic light propagating in air is incident on the surface of water. Which of the following will be the same for the reflected and refracted rays?

(A)Energy carried
(B)Speed
(C)Frequency✓ Correct
(D)Wavelength

Answer: (C)

Solution

Reflection and refraction occur when the incident light forces the surface electrons to oscillate; these oscillators re-radiate at exactly the frequency of the incident light. Hence the frequency of the reflected and refracted rays is the same as that of the incident ray.
The energy is split between the two rays, the speed changes on entering water, and (since

v = f λ

with

f

fixed) the wavelength of the refracted ray changes. Only the frequency is common.

(C) Frequency

CBSE Class 12 Board · 2023 · Single correct option

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