CBSE Class 12 Physics 2023 Outside Delhi Set 1 Paper

Question : 35

Total: 35

(a) Figure shows the variation of photoelectric current measured in a photo cell circuit as a function of the potential difference between the plates of the photo cell when light beams A, B, C and D of different wavelengths are incident on the photo cell. Examine the given figure and answer the following questions:

(i) Which light beam has the highest frequency and why?
(ii) Which light beam has the longest wavelength and why?
(iii) Which light beam ejects photoelectrons with maximum momentum and why?
OR
(b) What is the effect on threshold frequency and stopping potential on increasing the frequency of incident beam of light? Justify your answer.

Solution: 👈: Video Solution

(a) (i) Light beam B has the highest frequency. As the frequency increases, work function remaining same, the stopping potential increases.

For light beam B stopping potential is maximum. Hence, it has the highest frequency.

(ii) Light beam C has the lowest frequency. Hence, this beam has the longest wavelength.

(iii) Light beam B has the highest frequency. So, electrons ejected due to this radiation will have maximum kinetic energy and hence maximum momentum.

OR
(b) ● Stopping potential increases with increase of frequency of incident beam of light.
From Einsten's equation,
hv=hv0+eVS
v0 is constant for a particular substance. So, as v increases, VS increases.
● There is no effect on threshold frequency. Threshold frequency (v0) is a constant for a substance. If frequency of incident light is lower than this, no photoemission will take place. If frequency of incident light is higher than this, photoemission will take place.

Go to Question:

Prev Question