Question

Photocurrent recorded in the micro ammeter in an experimental set-up of photoelectric effect vanishes when the retarding potential is more than 0.8 V if the wavelength of incident radiation is 4950 Å. If the source of incident radiation is changed, the stopping potential turns out to be 1.2 V. Find the work function of the cathode material and the wavelength of the second source.

Answer 1

Data: V_o = 0.8 V, λ = 4950 Å = 4.950 × 10^-7 m, 

V_o ‘ = 1.2V, h = 6.63 × 10^-34 J∙s, c = 3 × 10⁸ m/s. 

(i) V_oe = hv – Φ = \(\cfrac{hc}{\lambda}\) – Φ 

∴ The work function of the cathode material,

(ii) V_o'e = \(\cfrac{hc}{\lambda'}\) - Φ

∴ \(\cfrac{hc}{\lambda'}\) = V_o'e + Φ

∴ The wavelength of the second sources,

\(\lambda'\) = \(\cfrac{hc}{V_o{'}e+\phi}\)