Photoelectric EffectHard

Question

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

Options

A.the stopping potential will be 0.2 V
B.the stopping potential will be 1.8 V
C.the saturation current will be 6.0 mA   
D.the saturation current will be 2.0 mA 

Solution

When the source is 3 times farther, number of photons falling on the surface becomes 1/9th but the frequency remains same. Hence stopping potential will be same i.e. 0.6V and saturation current become 1/9 × 18 mA = 2mA,

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