Eduprobe
Question:
A certain metallic surface is illuminated with monochromatic light of wavelength, λ. The stopping potential for photo-electric current for this light is 3V₀. If the same surface is illuminated with light of wavelength 2λ, the stopping potential is V₀. The threshold wavelength for this surface for photo-electric effect is:
4λ
λ/4
6λ
λ/6
Solution:
From photoelectric equation, K.E.max = hν - hνthreshold.. (i)
where ν is frequency of light
ν = c/λ
from equation (i)
3eV₀ = hc/λ - hc/λthreshold.. (ii)
eV₀ = hc/2λ - hc/λthreshold.. (iii)
multiplying (iii) by 3 and subtracting (ii)
0 = hc/2λ - 3hc/λthreshold
λthreshold = 4λ