Explanation

(b) From Einstein’s photoelectric equation the maximum kinetic energy of photoelectrons emitted from metal surface is $E_{K}$ and $W$ is work function, then
$\ \ \ \ \ \ \ \ \ \ \ \ E_{K} = hv - W$
If $v_{0}$ is threshold frequency, then
$\ \ \ \ \ \ W = hv_{0}$
$\therefore\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ E_{K} = hv - hv_{0} = h\left( v - v_{0} \right)$
From the above equation, it is clear that maximum kinetic energy of electron will increases almost linearly with increase in the frequency of the incident light.