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JEE Advanced 2019Paper 2
Exam
JEE Advanced
Year
2019
Paper
Paper 2
Subject
Physics
Chapter
Dual Nature of Matter

JEE Advanced 2019 · Paper 2 · Physics · Dual Nature of Matter

A perfectly reflecting mirror of mass M mounted on a spring...

A perfectly reflecting mirror of mass MM mounted on a spring constitutes a spring-mass system of angular frequency ΩΩ such that 4\piMΩh=1024m−2\dfrac{4\piMΩ}{h} = {10}^{24}{m}^{- 2} with hh as Planck's constant. NN photons of wavelength λ=8π×10−6m\lambda = 8\pi \times {10}^{- 6}m strike the mirror simultaneously at normal incidence such that the mirror gets displaced by 1\mum.1\mum . If the value of NN is x×1012,x \times {10}^{12}, then the value of xx is________.
[Consider the spring as massless]
A perfectly reflecting mirror of mass M mounted on a spring constitutes a spring-mass system of angular frequency Ω

Correct answer

0

Step-by-step solution

Total Momentum transferred on mirror =2Nhλ= \dfrac{2Nh}{\lambda} (for perfect reflection)
In an SHMSHM
{V}_\max = A . Ω
Where A=A = amplitude and Ω=Ω = angular frequency
⇒2Nhλ=MV(meanposition)⇒ \dfrac{2Nh}{\lambda} = M{V}_{\left(meanposition\right)}
{V(meanposition)=ΩA(whereA=1\mum)\begin{cases}{V}_{\left(meanposition\right)} = ΩA & \left(whereA = 1\mum\right)\end{cases}
⇒⇒\begin{cases}\dfrac{2Nh}{\lambda} = MΩA & \left(where\lambda = 8\pi \times {10}^{- 6}\right)\end{cases}$<br/><br />∴ N = \dfrac{\lambdaMΩA}{2h}<br/><br />⇒ N = \dfrac{MΩ\left({10}^{- 6}\right)\lambda}{2h} = \dfrac{MΩ8\pi \times {10}^{- 6} \times {10}^{- 6}}{2h}<br/><br />N = \dfrac{4\piMΩ}{h} \times {10}^{- 12}<br/><br />= {10}^{24} \times {10}^{- 12}<br/><br />N = 1 \times {10}^{12}<br/><br />x = 1$
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