JEE MAIN - Physics (2005 - No. 4)
A photocell is illuminated by a small bright source placed $$1$$ $$m$$ away. When the same source of light is placed $${1 \over 2}$$ $$m$$ away, the number of electrons emitted by photo-cathode would
increases by a factor of $$4$$
decreases by a factor of $$4$$
increases by a factor of $$2$$
decreases by a factor of $$2$$
Explanation
$$I \propto {1 \over {{r^2}}};{{{I_1}} \over {{I_2}}} = {\left( {{{{r_2}} \over {{r_1}}}} \right)^2} = {1 \over 4}$$
$${I_2} \to 4\,\,$$ times $${I_1}$$
When intensity becomes 4 times, no. of photoelectrons emitted would increase by $$4$$ times, since number of electrons emitted per second is directly proportional to intensity.
$${I_2} \to 4\,\,$$ times $${I_1}$$
When intensity becomes 4 times, no. of photoelectrons emitted would increase by $$4$$ times, since number of electrons emitted per second is directly proportional to intensity.
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