Question

When does the number of photoelectrons emitted per second from a metal surface increase?
A. The energy of incident photons increases
B. The frequency of incident light increase
C. The wavelength of incident light increase
D. The intensity of incident light increase

Answer 1

Hint: When light is incident on a metal surface, electrons are emitted known as photoelectrons. This phenomenon is called the photoelectric effect. The minimum energy under which the emission of photoelectrons takes place is known as the threshold energy.

Formula used:
The expression of kinetic energy of emitted electrons is,
\[K.E = E - W\]
Here, $E$ is the energy of the incident radiation and $W$ is the work function of a metal.

Complete step by step solution:
As we know that the kinetic energy of the emitted electron is,
\[K.E = E - W\]
Work function is a constant for a given material. If the energy is increased then the kinetic energy of the emitted electrons also increases. Now, we need to see how the number of photons increases or on what factors the number of photons increases.

The intensity of the light is directly proportional to the number of photons and we know that one photon emits only one electron at a time, if we increase the number of photons then the number of electrons also increases. That means when the intensity increases the number of photons also increases. And if we consider the other options, this happens only because of the change in the kinetic energy. Therefore, if the intensity of incident light increases then the number of photoelectrons emitted per second from a metal surface increases.

Hence, Option D is the correct answer.

Note:Work function of a metal is the minimum energy required to remove one electron from a metal surface. Work function can also be said as the characteristics of the surface and not the complete metal. As we know that the energy of the incident light or photons should be more than the work function of the metal for the photoemission to take place.