CBSE Class 12 Physics 2020 Delhi Set 1 Paper

Question : 25 of 37

Marks: +1, -0

Figure shows the stopping potential

( {\V}_0)

for the photoelectron versus

\;{1}/{λ}

graph, for two metals A and

B, λ

being the wavelength of incident light.

(a) How is the value of Planck's constant determined from the graph ?
(b) If the distance between the light source and the surface of metal

A

is increased, how will the stopping potential from electrons emitted from it be effected? Justify your answer.

Solution:

(a) Planck's constant can be determined from the gradient of the graph.

\;\text " Gradient "\;=\;{h c}/{e}

h=

Planck's constant

c=

Velocity of light in vacuum

e=

Charge of electron
Gradient to be measured from graph. The values of

c

and

e

are known. Hence,

h

can be determined.
(b) If distance between source of light and surface of metal A is increased, the intensity of incident light decreases. But stopping potential does not depend on the intensity of the incident light. So, the stopping potential will not be affected.

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