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Concepts Of Physics MCQ Edition [Volume 2]PhysicsPhotoelectric Effect and Wave–Particle Duality

A sphere of radius 1.00 cm is positioned in the path of a parallel beam of light of large aperture. The intensity of the light is 0.50 W cm ⁻² . If the sphere is not perfectly absorbing, how does the force on the sphere due to the light falling on it compare to the case where it completely absorbs the radiation?

Options

  1. AThe force is greater than when it completely absorbs the radiation
  2. BThe force is the same as when it completely absorbs the radiation
  3. CThe force depends on the specific absorption coefficient of the sphere
  4. DThe force is less than when it completely absorbs the radiation

Correct answer

B. The force is the same as when it completely absorbs the radiation

Step-by-step solution

Let the intensity of the incident light be I and the radius of the sphere be R . For a perfectly absorbing sphere, the light is completely absorbed by the projected cross-sectional area R^2 . The force exerted is the rate of change of momentum: F_ abs = I c R^2 For a perfectly reflecting sphere, consider an elemental ring on the surface of the sphere at an angle with respect to the direction of the incident beam. The area of this element is dS = 2 R^2 d . The power incident on this elemental area is P = I dS . Sinc

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