Question

This is my fourth time posting this problem, so if you are not 100% sure that you know how to solve it please leave it alone.

Exercise: Two light sources are used in a photoelectric experiment to determine the work function for a particular metal surface. When green light from a mercury lamp (λ = 546.1 nm) is used, a stopping potential of 0.894 V reduces the photocurrent to zero.

(a) Based on this measurement, what is the work function for this metal? __________ eV (b) What stopping potential would be observed when using light from a red lamp (λ = 642.0 nm)? ____________ V

Answer 1

(a) KE_max = eV_o = hc/λ - φ

=> Work function, φ = hc/λ - eV_o

=> φ = [6.63 * 10^-34 * 3 * 10⁸ / (546.1 * 10^-9)] - [1.6 * 10^-19 * 0.894] = 2.2 * 10^-19 J = 1.38 eV

(b) Stopping potential, V_o = hc/eλ - φ/e

=> V_o = [6.63 * 10^-34 * 3 * 10⁸ / (642 * 10^-9 * 1.6 * 10^-19)] - 1.38 = 0.556 V