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JEE Main 201910 AprilEvening Shift
Exam
JEE Main
Year
2019
Date
10 April
Shift
Evening Shift
Subject
Physics
Chapter
Dual Nature of Matter

JEE Main 2019 · 10 April · Evening Shift · Physics · Dual Nature of Matter

Light is incident normally on a completely absorbing surface with...

Light is incident normally on a completely absorbing surface with an energy flux of 25Wcm−225Wcm^{- 2} . If the surface has an area of 25cm225cm^{2} , the momentum transferred to the surface in 40min\text{40}\text{min} time duration will be:

Options

  1. A6.3×10−4Ns6.3 \times {10}^{- 4}Ns
  2. B5.0×10−3Ns5.0 \times {10}^{- 3}Ns
  3. C3.5×10−6Ns3.5 \times {10}^{- 6}Ns
  4. D1.4×10−6Ns1.4 \times {10}^{- 6}Ns

Correct answer

B. 5.0×10−3Ns5.0 \times {10}^{- 3}Ns

Step-by-step solution

The power of the incident light is P=25Wcm−2×25cm2P = 25Wc{m}^{- 2} \times 25c{m}^{2}
=625W= 625W
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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