Question 13: Dual Nature of Matter and Radiation

Question

Emission of electrons from a metal plate illuminated with monochromatic electromagnetic radiation will always take place provided

Accepted Answer

The correct choice is D.
Here's why:
PhotoelectricÃ¢ÂÂeffect threshold
Electrons are only emitted if each photon carries enough energy to overcome the metalÃ¢ÂÂs work function.  In symbols:
$$h
u \ge \phi$$
where
Ã¢ÂÂ¢ $h$ is PlanckÃ¢ÂÂs constant,
Ã¢ÂÂ¢ $
u$ is the light frequency,
Ã¢ÂÂ¢ $\phi$ is the work function (minimum energy to free an electron).
Why the other options fail
Ã¢ÂÂ¢ A (plate positively charged):  Charging might help pull electrons out, but if $h
u\phi$, electrons will indeed leave the metal surface.
Hence, Ã¢ÂÂthe work function is less than the energy of a single photon and the plate is unchargedÃ¢ÂÂ (option D) is the only choice that guarantees emission.

Answer

The plate is positively charged

Answer

The plate is negatively charged

Answer

The radiation is sufficiently intense

Answer

The work function of the plate is less than the energy of a single photon and the plate is uncharged

Dual Nature of Matter and Radiation

Emission of electrons from a metal plate illuminated with monochromatic electromagnetic radiation will always take place provided

Choose the correct answer: