Question

Photons of energy 5eV are incident on the cathode. Electrons reaching the anode have kinetic energies varying from 6eV to 8eV. Find the work function of the metal and state whether the current in the circuit is less than or equal to saturation current.
A. Work function of the metal is 2 eV
B. Work function of the metal is 3 eV
C. Current in the current is equal to saturation value
D. Current in the circuit is less than saturation value

Answer 1

Correct Answer - A::D
`KE_(max) = (5 - phi)eV`
when these electrons are accelerated through `5 V`
they will reach the anode with maximum energy `= (5- phi +5)eV`
`10 - phi = 8`
`phi = 2eV`
Current is less than saturation current because if slowest electron also reached the plate it would have `5 eV` energy at the anode, but there it is given that the minimum energy is 6 eV.