Question

The work function of lithium is 2.5 eV. The maximum wavelength of light that can cause the photoelectric effect in lithium is ______________

(a) 3980 Å

(b) 4980 Å

(c) 5980 Å

(d) 6980 Å

The question was posed to me during an online exam.

This interesting question is from PhotoElectric Effect topic in portion Quantum Physics of Engineering Physics I

Answer 1

Right option is (b) 4980 Å

Easiest explanation: Work function, Φ0 = hv0 or \(\frac{hc}{λ_0}\)

Therefore, λ0 = \(\frac{hc}{\Phi_0} \)

Here, Φ0 = 2.5 eV = 2.5 X 1.6 X 10^-19J

Maximum Wavelength, λ0 = \(\frac{hc}{\Phi_0} \) = 4.98 X 10^-7 m

λ0 = 4980 Å.