Question

when a point source of monochromatic ligth is at a distance of 0.2 m from a photoelectric cell , the cut off voltage and the saturation current are 0.6 V and 18mA resp . if the same source is placed 0.6 m away from the photoelectric cell then the stopping potential will be ?? ​

Answer 1

The stopping potential will be 2 m.A

Explanation:

• The intensity of light is inversely proportional to the square of the distance between the light source and photocell

Intensity, I∝1 / r^2 and saturation current ∝ I(intensity) ltbr

Saturation current ∝ 1 / r^2

= (Saturation current) - (final) / (Saturation current) - (initial)

= (r- initial)^2) / (r- (final)^2) implies (Saturation current) - (final)

= (0.2 x 0.2) / (0.6 x 0.6) x 18

= 2 m.A

Hence the stopping potential will be 2 m.A

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