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

In a photoelectric effect experiment, the emitter and collector plates are separated by 10 cm and connected via an ammeter without any cell (as shown in the figure). A magnetic field B is applied parallel to the plates. The emitter has a work function of 2.39 eV , and the incident light contains wavelengths ranging from 400 nm to 600 nm . Determine the minimum value of B such that the current registered by the ammete

Options

  1. A5.70 10⁻⁵ T
  2. B1.42 10⁻⁵ T
  3. C2.85 10⁻⁴ T
  4. D2.85 10⁻⁵ T

Correct answer

D. 2.85 10⁻⁵ T

Step-by-step solution

The maximum kinetic energy of the emitted photoelectrons corresponds to the minimum wavelength of the incident light, = 400 nm . The energy of the incident photon is given by: E = hc = 1242 eV nm 400 nm = 3.105 eV Using Einstein's photoelectric equation, the maximum kinetic energy K_ is: K_ = E - = 3.105 eV - 2.39 eV = 0.715 eV For the ammeter to register zero current, the magnetic field must be strong enough to prevent even the most energetic photoelectrons from reaching the collector plate. Assuming the limiting

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