Question

Select the incorrect statement:
A.K.E. of photo-electron does not depend upon the wavelength of incident radiation
B. Photoelectric current depends on intensity of incident radiation and not on frequency
C. Stopping potential depends on frequency of radiation and not on intensity
D. None of these

Answer 1

Hint: The mechanism by which the electrons get ejected from the surface of a metal when light of suitable frequency strikes on it is called photoelectric effect. The emitted electrons are called photoelectrons.

Complete Solution :
The results observed in photoelectric experiment are as follows:
1. No Time Lag Between the Striking of Light and Ejection of Electrons : It was seen that as soon as the light of suitable frequency strikes the metal surface, photoelectrons are ejected.
2. Threshold Frequency : It is the minimum frequency of light needed to cause photoelectric effect. Below this frequency the photoelectrons cannot be ejected. Threshold frequency is symbolised as (${{v}_{0}}$). So, it was seen that if the frequency of light ($v$) is greater than the threshold frequency ($v$) then only electrons are ejected accompanied with maximum possible kinetic energy.
3. Number of Photoelectrons : The number of electrons ejected is proportional to the intensity or brightness of light striking the metal but do not depend upon the frequency of light
4. Kinetic energy of the photoelectrons : The kinetic energy of the ejected electrons (photoelectrons) depend upon the frequency of the light used.
Now from the above theories we conclude wavelength increases, speed decreases, so KE also decreases and vice versa.
So, the correct answer is “Option A”.

Note: The photoelectric effect is used in a wide range of applications, starting from the cathode ray of televisions, to the night vision devices. It can also be used to determine the energy levels of electrons.