Dual Nature of Matter

JEE Main level, single correct, medium

171 of 200

Question 171 of 200

Light is incident normally on a completely absorbing surface with an energy flux of 25Wcm−225Wc{m}^{-2} . If the surface has an area of 25cm225c{m}^{2} , the momentum transferred to the surface in 40min\text{40} \text{min} time duration will be:

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Answer: (B) 5.0×10−3Ns5.0\times {10}^{-3}Ns

The power of the incident light is P=25Wcm−2×25cm2P=25 W c{m}^{-2}\times 25 c{m}^{2}
=625W=625 W
Energy incident per second, E=hcλ=625JE=\dfrac{hc}{\lambda }=625J
Momentum incident per second, p=Ec=hλ=625cp=\dfrac{E}{c}=\dfrac{h}{\lambda }=\dfrac{625}{c}
∴∴ Total momentum transferred to the surface =625c×40×60=\dfrac{625}{c}\times 40\times 60
=5×10−3Ns=5\times {10}^{-3} Ns

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