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KCET2020PhysicsDual Nature of Matter

A light beam of intensity 20 ~W / cm ² is incident normally on a perfectly reflecting surface of sides 25 ~cm 15 ~cm . The momentum imparted to the surface by the light per second is

Options

  1. A2 10⁻⁵ ~kg - ms ⁻¹
  2. B1 10⁻⁵ ~kg - ms ⁻¹
  3. C5 10⁻⁵ ~kg - ms ⁻¹
  4. D1.2 10⁻⁵ ~kg - ms ⁻¹

Correct answer

C. 5 10⁻⁵ ~kg - ms ⁻¹

Step-by-step solution

Given, intensity, I=20 ~W / cm ² Area of surface, A=(25 15) cm ² and time, t=1 ~s The intensity of light of energy E is given by aligned I &= E A t 20= E 25 15 1 E &=20 25 15 ~J aligned The momentum imparted to a perfectly reflecting surface is given by p= 2 E c = 2 20 25 15 3 10⁸ =5 10⁻⁵ ~kg ~ms ⁻¹

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