Question

Light of frequency 1.5 times the threshold frequency is incident on a photosensitive material. What will be the photoelectric current if the frequency is halved and intensity is doubled?

• A. doubled
• B. four times
• C. one-fourth
• D. zero

Answer 1

The Correct Option is D

The question involves the photoelectric effect, which is a phenomenon where electrons are ejected from a material when it is exposed to light of a certain minimum frequency, known as the threshold frequency. The photoelectric effect can be understood using the equation:

\(E = h f\)

Where:

• \(E\) is the energy of the incident photons.
• \(h\) is Planck's constant.
• \(f\) is the frequency of the incident light.

For photoelectric emission to occur, the frequency of the incident light must be greater than the threshold frequency \(f_0\). Given:

• The initial frequency of the light is 1.5 times the threshold frequency: \(f = 1.5 f_0\).

If the frequency is halved, the new frequency \(f'\) becomes:

\(f' = \frac{f}{2} = \frac{1.5 f_0}{2} = 0.75 f_0\)

Now, the new frequency \(f'\) is less than the threshold frequency \(f_0\). As a result:

• No photoelectric emission will occur because the incident light frequency is below the threshold frequency required to liberate electrons from the material.

Regarding the photoelectric current, which is directly related to the number of electrons emitted, since no electrons are emitted when the frequency is below the threshold frequency, the photoelectric current will be zero, regardless of the intensity of the light.

Therefore, the correct answer is:

• Zero