The work function of a substance is 4.0 eV. The longest wavelength of light that can cause photoelectron emission from this substance is approximately

Options

(a) 540 nm
(b) 400 nm
(c) 310 nm
(d) 220 nm

Correct Answer:

310 nm

Explanation:

hc / λ(m) = Work function ⇒ λ(max) = hc / w

λ(max) = (6.6 x 10⁻³⁴) × (3 × 10⁸) / (4 × 1.6 × 10⁻¹⁹)

λ(max) = [(6.6 × 3) / (4 × 1.6)] × 10⁻⁷ m

λ(max) = 310 nm