JEE Mains · Physics · STD 12 - 11. Dual nature of radiation and matter
A small mirror of mass \(m\) is suspended by a massless thread of length \(l\). Then the small angle through which the thread will be deflected when a short pulse of laser of energy \(E\) falls normal on the mirror ( \(\mathrm{c}=\) speed of light in vacuum and \(\mathrm{g}=\) acceleration due to gravity)
- A \(\theta=\frac{3 \mathrm{E}}{4 \mathrm{mc} \sqrt{\mathrm{g} l}}\)
- B \(\theta=\frac{\mathrm{E}}{\mathrm{mc} \sqrt{\mathrm{g} l}}\)
- C \(\theta=\frac{\mathrm{E}}{2 \mathrm{mc} \sqrt{\mathrm{gl}}}\)
- D \(\theta=\frac{2 \mathrm{E}}{\mathrm{mc} \sqrt{\mathrm{g} l}}\)
Answer & Solution
Correct Answer
(D) \(\theta=\frac{2 \mathrm{E}}{\mathrm{mc} \sqrt{\mathrm{g} l}}\)
Step-by-step Solution
Detailed explanation
Force due to beam assuming complete reflection \(\mathrm{F}=\frac{2 \mathrm{P}}{\mathrm{C}}=\frac{2}{\mathrm{C}} \frac{\mathrm{dE}}{\mathrm{dt}} ; \mathrm{P}\) is power So change in momentum of mirror.…
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