Question

A photon has momentum 9 X 10-28kgms-1.What will be the stopping potential, if photo cathode has work function 1.3eV?

Answer 1

Momentum of photon , P = 9 × 10⁻²⁸ Kgm/s
We know, according to De- broglie's wavelength,
λ = h/P
= h/9 × 10⁻²⁸

Now, use formula
Maximum kinetic = hc/λ - Φ Here, Φ is work function ,
K.Emax = hc/{h/9 × 10⁻²⁸} J - 1.3eV
K.Emax = 3 × 10⁸ × 9 × 10⁻²⁸/1.6 × 10⁻¹⁹ eV - 1.3 eV
= 2.7/1.6 - 1.3 eV
= (2.7 - 2.08)/1.6 eV
= 0.62/1.6 eV = 0.3875eV

Now, shopping potential = K.Emax [Here V₀ is stopping potential]
eV₀ = 0.3875eV
hence, stopping potential = 0.3875V