This is my fourth time posting this problem, so if you are not 100% sure that yo

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 ( = 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 ( = 642.0 nm)? ____________ V

Explanation / Answer

(a) KEmax = eVo = hc/ -

=> Work function, = hc/ - eVo

=> = [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, Vo = hc/e - /e

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

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