Figure shows the stopping potential (V₀) 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 Plank'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 for the electrons emitted from it be effected? Justify your answer. [2020 | Delhi | Section - B | SET - 1 SET - 3, Q.25 Q.22] Solution :
a) Using Einstein's Photoelectric equation
Kmax=hν-hν₀
eV₀=hν-hν₀
eV₀=hν-W₀
V₀=(hν-W₀)/e
V₀=hν/e-W₀/e
V₀=hc/λe-W₀/e
V₀=(hc/e)(1/λ) + (-W₀/e)
On comparing with y=mx+c
slope (m) = hc/e
y-intercept (c) =-W₀/e
Now, Planck Constant, (h)
m = hc/e
h = me/c
b) On increasing the distance between the light source and metal A, the intensity of the radiation / light source will decrease but the frequency of radiation will remain same. The stopping potential depends on the frequency of the radiations and not on the intensity of light. Hence, there will be no effect on the stopping potential for the electrons.
