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NEETPhysicsDual Nature of Matter

A monochromatic light source of power P emits photons of wavelength . The light falls normally on a perfectly absorbing surface. The total momentum delivered to the surface per second is ( c is the speed of light in vacuum and h is Planck's constant):

Options

  1. AP hc
  2. BP
  3. CPc
  4. DP c

Correct answer

D. P c

Step-by-step solution

The energy of a single photon is E = hc . The number of photons emitted per second is n = P E = P hc . The momentum of a single photon is p = h . The total momentum delivered to the surface per second is the product of the number of photons per second and the momentum of each photon. Total momentum per second = n p = ( P hc ) ( h ) = P c . Alternatively, since the total energy incident per second is P , and momentum p = E c , the total momentum delivered per second is simply P c . Answer: P c

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