Question

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

Answer 1

According to Einstein's equation

$K.E=h\nu -h{\nu }_0$

So, ${K.E}_{max}=(5-\varphi )eV$

When these electrons are accelerated through $5V$, they will reach the anode with maximum energy$=(5-\varphi +5)eV$

$\therefore 10-\varphi =8$

$\varphi =2eV$

Current is less than saturation current because if slowest electron also reaches the plate it would have $5eV$ energy at the anode, but it is given that the minimum energy is $6eV$, So current in the circuit is less than the saturation value