First slide

Photo Electric Effect

Question

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

Easy

A

0.65 eV
B

1.0 eV
C

1.3 eV
D

1.5 eV

Solution

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

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