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In a photoelectric cell, the cathode material is replaced so that its work function increases from W1 to W2, with W2 > W1. If the photocurrent before and after the change are I1 and I2 respectively, and all other conditions are kept the same (with hν > W2), which relation is correct?

1. I1 = I2
2. I1 < I2
3. I1 > I2
4. I1 < 2I2

Correct answer: I1 = I2

Solution

As long as hv exceeds the work function, the saturation photocurrent is set by the number of incident photons (intensity), which is unchanged. Hence I1 = I2.

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