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Physics · 2025 · 3 marks
CBSE 2025 · Region 2 · Set 3 · Q25
(a) The amplitude of a light wave becomes n times. This results in intensity of the wave becoming m times. What is the relation between n and m? (b)…
(a)
The amplitude of a light wave becomes n times. This results in intensity of the wave becoming m times. What is the relation between n and m?
(b)
White light is incident on three identical surfaces-a black surface, a yellow surface and a white surface, one by one. For which surface, the pressure exerted on the surface by the incident light will be
(i)
maximum (ii) minimum? Justify your answer.
Marking-scheme solution
(a)
Intensity (I) $\displaystyle \propto$ (amplitude) $\displaystyle ^{2}$
$\displaystyle \Rightarrow m=n^{2}$
(b)(i)
White surface
As white surface will reflect maximum light falling on it, the change in momentum of light will be maximum and as a consequence the pressure exerted by the light will be maximum.
(ii)
Black surface
As black surface absorbs maximum light falling on it, the change in momentum of light will be minimum and as a consequence the pressure exerted by the light will be minimum.
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