Question

While studying photoelectric emission from a given surface, the wavelength of the incident radiation is changed from 600 nm to 400 nm, keeping the intensity of radiation the same. Then ______.

विकल्प

• cut-off potential will decrease.

• cut-off potential will increase.

• saturation current will decrease.

• saturation current will increase.

Answer 1

While studying photoelectric emission from a given surface, the wavelength of the incident radiation is changed from 600 nm to 400 nm, keeping the intensity of radiation the same. Then cut-off potential will increase.

Explanation:

The maximum kinetic energy of the photoelectrons, which is dependent on the energy of the incident photons, determines the cut-off potential, also known as the stopping potential.

If the frequency is above the threshold, the saturation current is determined by the number of photoelectrons released per second, which is proportional to the intensity (number of photons).

Einstein’s photoelectric equation:

eV_s = hv − Φ

= `(h c)/lambda - phi`

Where V_s is the stopping potential, λ is the wavelength, and ϕ is the work function.

The wavelength is decreased from 600 nm to 400 nm.

As λ decreases, the energy of each photon E = `(h c)/lambda` increases.

From the equation eV_s = `(h c)/lambda - phi`, an increase in `(h c)/lambda` results in an increase in V_s, provided the intensity is kept constant.

The intensity (energy per unit area per unit time) determines the saturation current. In fact, the number of photons per second reduces slightly but does not increase if the intensity remains constant while the wavelength decreases. The alteration in stopping potential is the most noticeable effect.