Question

The photons, of light of wavelength λ, have the same momentum as that of electrons (mass = 9.31×10^–31 kg) moving with a speed of 1.6×10³ m/s. If this light (of wavelength λ ) is made to fall on a photosensitive surface of work function 1.793 eV, the ‘stopping potential’, needed to make the ‘photo current’ zero, is 

(1) 2.5 V 

(2) 2.0 V 

(3) 1.5 V 

(4) 1.0 V

Answer 1

Correct option : (4) 1.0 V

Explanation :

Momentum of photon = h/ λ = momentum of electron = mv

= 27.93×10^–1 eV = 2.793 eV 

Work function = 1.793 eV 

∴ Energy of the most energetic emitted photoelectric = (2.793–1.793) eV = 1 eV

∴ Stopping potential = 1 V