Question

Photoelectrons are ejected from a metal when light of frequency v falls on it. Pick out the wrong statement from the following A)-No electrons are emitted if v less than W/h , where W is the work function of the metal B)-The ejected of the photoelectrons is instantaneous. C)-The maximum energy of the photoelectrons is hv. D)-The maximum energy of the photoelectrons is independent of the intensity of the light.

Answer 1

The incorrect statement is that the maximum energy of photoelectrons is hv. The maximum kinetic energy is actually the energy of the incident photon minus the work function of the metal (Kmax = hv - W), and is independent of light intensity.

Step-by-step explanation:

The inaccuracy lies in the statement that 'The maximum energy of the photoelectrons is hv'. The correct expression is that the maximum kinetic energy (Kmax) of a photoelectron is calculated by subtracting the work function (W) of the metal from the energy of the incident photon (hv), which is expressed in the equation Kmax = hv - W. Hence, the maximum energy of the photoelectrons depends on both the frequency of the light and the work function, and is not simply hv. The frequency (v) of the incident light has to be above the threshold frequency; otherwise, no photoelectrons are emitted (v < W/h), and the emission of photoelectrons is instantaneous upon the absorption of photons with sufficient energy. The maximum energy of the photoelectrons is also independent of the intensity of the light but depends on the frequency of the light.

Answer 2

The incorrect statement is C) "The maximum energy of the photoelectrons is hv."

Let's analyze each statement one by one:

A) "No electrons are emitted if v is less than W/h, where W is the work function of the metal."

This statement is correct. The energy of a photon (E) is directly proportional to its frequency (v) by the equation E = hv, where h is Planck's constant. For photoemission to occur, the energy of the incident photons must be greater than or equal to the work function (W) of the metal. So, if v is less than W/h, no electrons will be emitted.

B) "The ejection of the photoelectrons is instantaneous."

This statement is also correct. When photons with sufficient energy strike the metal surface, they can eject electrons almost instantaneously through the photoelectric effect. This process occurs on a very short timescale, typically within femtoseconds.

C) "The maximum energy of the photoelectrons is hv."

This statement is incorrect. The energy of the ejected photoelectrons can reach a maximum value of hv - W, where W is the work function of the metal. The energy of the photon (hv) is partially used to overcome the work function (W) and the rest becomes the kinetic energy of the emitted photoelectrons.

D) "The maximum energy of the photoelectrons is independent of the intensity of the light."

This statement is correct. The kinetic energy of the emitted photoelectrons depends on the energy of the incident photons (which is determined by their frequency) and the work function of the metal. It is not dependent on the intensity (brightness) of the light. Increasing the intensity of the light increases the number of photoelectrons ejected but not their individual kinetic energies.

So, the incorrect statement is C) "The maximum energy of the photoelectrons is hv."