Light is incident normally on a completely absorbing surface with an energy flux of   25   W &#160…

Light is incident normally on a completely absorbing surface with an energy flux of  25 W cm-2 . If the surface has an area of  25 cm2 , the momentum transferred to the surface in 40 min time duration will be:
  1. 6.3×10-4 N s
  2. 5.0×10-3 N s
  3. 3.5×10-6 N s
  4. 1.4×10-6 N s

Solution

The power of the incident light is P=25  W cm-2×25 cm2
=625 W
Energy incident per second, E=hcλ=625 J
Momentum incident per second, p=Ec=hλ=625c
∴ Total momentum transferred to the surface =625c×40×60
=5×10-3 N s

Asked in: JEE Main 2019 (10 Apr Shift 2)

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