First slide

Photoelectric effect and study of photoelectric effect

Question

When a point source of monochromatic light is at a distance of 0.2 m from a photoelectric cell, the cut-off voltage and the saturation current are 0.6 volt and 18 mA respectively. If the same source is placed 0.6 m away from the photoelectric cell, then

Moderate

A

The stopping potential will be 0.2V
B

The stopping potential will be 0.6 V
C

The saturation current will be 6 mA
D

The saturation current will be 18 mA

Solution

Cut-off voltage is independent of intensity and hence, remains the same. Since distance becomes 3 times, intensity (I) becomes $\frac{I}{9}$ . Hence, photocurent also decreases by this factor i.e., becomes $\frac{18}{9} = 2$ mA.

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