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

A metal plate is illuminated by a monochromatic beam of light with a wavelength of 400 nm , and a negative potential of 1.1 V is required to halt the photocurrent. Determine the threshold wavelength for the metal.

Options

  1. A295 nm
  2. B620 nm
  3. C1127 nm
  4. D827 nm

Correct answer

B. 620 nm

Step-by-step solution

According to Einstein's photoelectric equation: E = + K_ max The energy of the incident photon is given by: E = hc = 1240 eV nm 400 nm = 3.1 eV The maximum kinetic energy of the photoelectrons is related to the stopping potential V₀ as: K_ max = eV₀ = 1.1 eV Substituting these values into the photoelectric equation: = E - K_ max = 3.1 eV - 1.1 eV = 2.0 eV The threshold wavelength ₀ is given by: ₀ = hc = 1240 eV nm 2.0 eV = 620 nm

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