Question

In photoelectric effect, the KE of electrons emitted from the metal surface depends upon
A. Intensity of light
B. frequency of incident light
C. velocity of incident light
D. Both intensity and velocity of light

Answer 1

Hint: The phenomena of emission of the electron from the surface of metal upon incidence of light having a certain frequency which is greater than the threshold frequency is known as photoelectric effect.

Formula used:
\[KE = h\nu - \varphi \],
Here \[KE\] is the kinetic energy of the emitted electrons, h is the Plank’s constant, \[\nu \] is the frequency of the light and \[\varphi \] is the work function of the material.

Complete step by step solution:
The work function of the material of the photo-plate is the minimum energy needed to eject the electron from the surface of the material. In metal the valence shell electrons needed some energy to come out of the shell of the atom of the metal. When a photon is incident on the surface of the metal then these electrons gain energy during the collision with the photon and gain energy which must be sufficient to overcome the valence electron energy and comes out of the metal. These electrons are called the photoelectrons.

When a photon undergoes collision with the electrons then part of the energy is used to overcome the energy with which the electrons are bound to the shell of the atom of the metal and the rest of the energy gets transferred to the electrons as the kinetic energy.So, the kinetic energy of the photoelectrons is the difference between the energy of the photon and the work function of the metal.

The work function of a particular metal is constant and hence, the kinetic energy depends on the energy of the photon.
\[KE = h\nu - \phi \]
Hence, the kinetic energy of the electrons emitted from the metal surface depends upon the frequency of the incident light.

Therefore, the correct option is B.

Note: The number of electrons emitted is proportional to the number of photons incident on the metal surface per second, i.e. the intensity of the light. But the kinetic energy doesn’t depend on the number of photons incident per unit time.