The minimum energy necessary to overcome the attractive force between the electron and the surface of silver metal is 7.52 × 10−19 J. What will be the maximum kinetic energy of the electrons ejected from silver which is being irradiated with ultraviolet light having a wavelength 360 Å?
From Planck's Theory,
E = hv = hcλ
Therefore,
Energy absorbed = hcλ
= 6.625 × 10−34 × 3.0 × 1010360 × 10−8
= 5.52 × 10−18 joule
Now this energy is used in overcoming forces of attraction between surface of metal and imparting velocity to electron, therefore,
Eabsorbed = E used in attractive forces + Kinetic energy of electron
∴ Kinetic energy = 5.52 × 10−18 − 7.52 × 10−19 joule
= 47.68 × 10−19 joule