Question

A photon of wavelength 3310 Å falling on a photo cathode ejects an electron of energy 3 × 10^–19 J and one of wavelength 5000 Å ejects an electron of energy 0.972 × 10^–19 J. Calculate the value of Planck’s constant and the threshold wavelength for the photo cathode. 

Answer 1

In the first case,

In the second case,

Subtracting one from the other,

h = 6.62 × 10^–34 J-s

Substituting this value of h, W₀ = 3 × 10^–19 J