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Q)

When a monochromatic point source of light is at a distance 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 photocell, then choose the correct option:

$\begin {array} {1 1} (1)\;the\: stopping\: potential \: will\: be\: 0.2 \: V & \quad (2)\;the \: stopping \: potential \: will \: be\: 0.6\: V \\ (3)\;the \: saturation\: current\: will \: be\: 2 \: mA & \quad (4)\;the\: saturation\: current \: will\: be\: 6 \: mA \end {array}$

$\begin {array} {1 1} (a)\;1 \: and \: 3 & \quad (b)\;2 \: and \: 3 \\ (c)\;1\: and \: 4 & \quad (d)\;2\: and \: 4 \end {array}$

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A)
Ans : (b)
Since distance has been increased by a factor of 3 therefore
intensity has been reduced by factor of 9.