Question

Silver has a work function of $4.7 \,eV$. When ultraviolet light of wavelength $100 \,nm$ is incident upon it, a potential of $7.7$ volt is required to stop the photoelectrons from reaching the collector plate. Find the potential (in volt) required to stop photo electrons when light of wavelength $200 \,nm$ is

Answer 1

Given $\phi=4.7\, eV$
for $ \lambda=100\, nm , $
$V _{ s }=7.7\, volt$
for $\lambda=200 \,nm$
$V _{ s }=?$
$eV _{ s }=\frac{ ch }{\lambda}-\phi$
$=\frac{3 \times 10^{8} \times 6.62 \times 10^{-34}}{2 \times 10^{-7} \times 1.6 \times 10^{-19}}-4.7$
$=6.2-4.7=1.5 \,V$
$\Rightarrow V _{ s }=1.5 \,volt$