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(B) The intensity $I$ of light from a point source at a distance $d$ is given by $I = \frac{P}{4\pi d^2}$,where $P$ is the power of the source.Thus,$I

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Become four times

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(B) The intensity $I$ of light from a point source at a distance $d$ is given by $I = \frac{P}{4\pi d^2}$,where $P$ is the power of the source.Thus,$I \propto \frac{1}{d^2}$.When the distance is reduced to $d' = d/2$,the new intensity $I'$ becomes $I' = \frac{P}{4\pi (d/2)^2} = \frac{P}{4\pi (d^2/4)} = 4 	imes \frac{P}{4\pi d^2} = 4I$.The number of photoelectrons emitted per second is directly proportional to the intensity of the incident light $(N \propto I)$.Since the intensity becomes $4$ times,the number of electrons emitted per second will also become $4$ times the original value.

$A$ photoelectric cell is illuminated by a point source of light kept at a distance $d$. If the distance is reduced to $d/2$,then the number of electrons emitted per second will be:

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