Dual Nature of Matter

JEE Main level, single correct, medium

137 of 200

Question 137 of 200

A small object at rest, absorbs a light pulse of power 20mW20mW and duration 300ns300ns. Assuming speed of light as 3×108ms−13\times {10}^{8}m{s}^{-1}. The momentum of the object becomes equal to :

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Answer: (B) 2×10−17kgms−12\times {10}^{-17}kgm{s}^{-1}

Momentum p=Energy(E)Speedoflight(c)p=\dfrac{Energy\left(E\right)}{Speedoflight\left(c\right)}
=Power×timec=\dfrac{Power\times time}{c}
=(20×10−3W)(300×10−9s)3×108ms−1=\dfrac{\left(20\times {10}^{-3}W\right)\left(300\times {10}^{-9}s\right)}{3\times {10}^{8}m{s}^{-1}}
=2×10−17kgms−1=2\times {10}^{-17}kgm{s}^{-1}
As momentum is conserved, therefore momentum of object will be 2×10−17kgms−12\times {10}^{-17}kgm{s}^{-1}.

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