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  4. When the energy of the incident radiation is increased by 20 %, the kinetic energy of the photoelectrons emitted from a metal surface increased from 0.5 eV to 0.8 eV. The work function of the metal is

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Q. When the energy of the incident radiation is increased by $20 \%, $ the kinetic energy of the photoelectrons emitted from a metal surface increased from $0.5 \,eV$ to $0.8 \,eV$. The work function of the metal is

AIPMTAIPMT 2014Dual Nature of Radiation and Matter

Solution:

According to Einstein's photoelectric equation.
The kinetic energy of emitted photoelectrons is $K=h \nu-\phi_{0}$
where $h \nu$ is the energy of incident radiation and $\phi_{0}$ is
work function of the metal.
As per question,
$0.5 e V=h v-\phi_{0} \ldots(i)$
$0.8 e V=1.2 h v-\phi_{0} \ldots(i i)$
On solving eqns. (i) and (ii), we get
$\phi_{0}=1.0\, eV$