Question

A monochromatic ray of photons of energy $5eV$ are incident on cathode. Electrons reaching the anode have kinetic energies varying from $6eV$ to $8eV$ . Choose the current option.

• A. work function of the metal is $1eV$
• B. work function of the metal is $3eV$
• C. current in the circuit is equal to saturation value
• D. current in the circuit is less than saturation value.

Answer 1

Answer: (D)

${\left(KE\right)}_{max}=(5-\varphi )eV$
when these electrons are accelerated through $5\text{V}$ , they will reach the anode with maximum energy $=(5-\varphi +5)eV$
$10-\varphi =8\varphi =2eV$
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 $6eV$ .