Question

When a centimeter thick surface is illuminated by light of wavelength l,the stopping potential is V. When the same surface is illuminated by light of wavelength 2l,the stopping potential is V/3. The threshold wavelength for the surface is

Answer 1

let the threshold wavelength = λ
the energy required by photo electrons to escape = h c/λ

e V + hc/λ = hc/l
e V/3 + hc/λ = hc/2l

=>  h c/l = 4/3 * eV
=>  hc/λ = 1/3 * eV 
=>   λ = 4 l

Answer 2

Answer:

This is the answer

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