Question

Photons of energy 5 eV are incident on cathode. Electrons reaching the anode have kinetic energies varying from 6eV to 8eV.

• A. Work function of the metal is 1 eV
• B. Work function of the metal is 2 eV
• C. Current in the circuit is equal to saturation value
• D. Current in the circuit is less than saturation value.

Answer 1

Answer: (B), (D)

Work function of the metal is 2 eV
Current in the circuit is less than saturation value.

According to Einstein's equation $KE=hv-h{v}_0$
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 reached the plate it would have 5eV energy at the anode, but there it is given that the minimum energy is 6eV.

So, the answers are option (B) & (D).