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NEET2016PhysicsDual Nature of MatterActual

When a metallic surface is illuminated with radiation of wavelength λ , the stopping potential is V . If the same surface is illuminated with radiation of wavelength 2 λ , the stopping potential is V 4 . The threshold wavelength for the metallic surface is:

Options

  1. A4 λ
  2. B5 λ
  3. C5 2 λ
  4. D3 λ

Correct answer

D. 3 λ

Step-by-step solution

Given, Stopping potential is V when the metal is illuminated with λ . Stopping potential is V 4 when the metal is illuminated with 2 λ . In photo electric effects e V 0 =   h ν − W e V 0 = h c λ - W e V = h c λ - W ...(i) e V 4 = h c 2 λ - W ....(ii) From (i) and (ii) h c λ - W = 4 h c 2 λ - W h c λ - W = 2 h c λ - 4 W 3 W = h c λ ⇒ W = h c 3 λ h c λ m a x = h c 3 λ ⇒ λ m a x = threshold wavelength = 3 λ

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