Question

Light of wavelength λ falls on a metal with work-function hc/λ₀. Photoelectric effect will take place only if
(a) λ ≥ λ₀
(b) λ ≥ 2λ₀
(c) λ ≤ λ₀
(d) λ < λ₀/2

Answer 1

(c) λ ≤ λ₀

As the work-function of the metal is hc/λ₀, its threshold wavelength is λ₀.
For photoelectric effect, the wavelength of the incident light should be less than or equal to the threshold wavelength of the metal on which light is incident.