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  4. If the maximum kinetic energy of emitted photo electrons from a metal surface of work function 2.5 eV, is 1.7 eV. If wavelength of incident radiation is halved, then stopping potential will be

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Q. If the maximum kinetic energy of emitted photo electrons from a metal surface of work function 2.5 eV, is 1.7 eV. If wavelength of incident radiation is halved, then stopping potential will be

AIIMSAIIMS 2018Dual Nature of Radiation and Matter

Solution:

Energy of incident photons,
$h\upsilon=\phi_{0}+K_{max} = 2.5+1.7=4.2 \,\,eV$
$\because \quad\upsilon\lambda=c and \upsilon^{'} \frac{\lambda}{2}=c\,\,\Rightarrow \,\,\upsilon^{'} =2\upsilon$
According to Einstein’s photoelectric equation,
$eV_{0}=h\upsilon^{'} -\phi_{0}=h\left(2\upsilon\right)-\phi_{0}=2\times4.2-1.7$
$\quad=6.7\,eV\,\,\Rightarrow \,\,V_{0}=6.7\,V$