PYQ NEET- Dual Nature Of Matter And Radiation L-7

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

A) $+3 V$

B) $+4 \mathrm{~V}$

C) $-1 \mathrm{~V}$

D) $-3 \mathrm{~V}$

Answer: $-3 \mathrm{~V}$#

Solution:#

Stopping potential is the voltage which is needed to stop energetic photo electron for reaching towards cathode.

Stopping potential, $\phi=\mathrm{E}-\mathrm{K}_{\max }$ $2 \mathrm{eV}=5 \mathrm{eV}-\phi$ or $\phi=3 \mathrm{eV}$

Now $\mathrm{eV}_0=\mathrm{E}^{\prime}-\phi=6 \mathrm{eV}-3 \mathrm{eV}=3 \mathrm{eV}$

Hence stopping potential is $-3 \mathrm{~V}$