Question

Photons with energy $5eV$ are incident on a cathode $C$ in a photoelectric cell. The maximum energy of emitted photoelectrons is $2eV$. When photons of energy $6eV$ are incident on $C$, no photoelectrons will reach the anode $A$, if the stopping potential of $A$ relative to $C$ is

• A. $-1V$
• B. $-3V$
• C. $+3V$
• D. $+4V$

Answer 1

Answer: (B)

When $5eV$ is incident the kinetic energy is $2eV$ it simply means the work function is $W=5eV-2eV=3eV$

Similarly When $6eV$ is incident the kinetic energy should be $6eV-W=6eV-3eV=3eV$

it simply means to stop them we need a $negative$ potential at anode equal to $\frac{3eV}{e}=3V$

So answer is $-3V$ i.e. option B is correct.