Ejection of the photoelectron from metal in the photoelectric effect experiment can be stopped by applying 0.5 V when the radiation of 250 nm is used. The work function of the metal is:

From Ejection photoelectron ⇌ hv = hvo + K.E.
hvx = Φ + Stopping pot
⇌ Φ = hcx - S.P. = 6.6 × 10⁻³⁴ × 3 × 10⁸ / 250 × 10⁻⁹ × 1.6 × 10⁻¹⁹ - 0.5 × 1.6 × 10⁻¹⁹
= 6.6 × 3 / 250 × 1.6 × 10⁻¹⁹ - 0.5 × 1.6 × 10⁻¹⁹
= 4.95 × 10⁻¹⁹ - 0.5 × 1.6 × 10⁻¹⁹
= 4.95 - 0.8
≈ 4.15 eV ≈ 4.5 eV