Question

Three laser guns labelled as $$I, II$$ and $$III$$ have power $$2,3$$ and $$5\ W$$ (not necessary in the same order) are used to produce photocurrent from metal plate. Number of photons emitted by laser guns are $$4\times 10^{18}, 5\times 10^{18}$$ and $$9\times 10^{18}$$ per second. Metal plate have thershold energy $$4.5\times 10^{-19}\ J$$. Neither the power nor the number of photons emitted by a particular laser gun is known and it is known that all capable photons emit a photoelectron
Minimum photocurrent which must be passed through the circuit is

Answer 1

Correct option is D. $$0.64\ A$$