Explanation

(c) When light waves of differing frequencies are made incident on the same surface, the stopping potential ($V_{s}$) differ as is evidenced from Einstein’s photoelectric equation given by
$hv - hv_{0} = eV_{s}$
where $h$ is Planck’s constant, $v,v_{0}$ the frequencies and $e$ the charge.
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Hence, ${\ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ \ V}_{s} = \frac{hv}{e} - \frac{hv}{e}$ …(i)
Comparing Eq. (i) with straight line equation
$y = mx + c$
Slope $m = \frac{h}{e}$
$Where\ \ \ h = 6.6 \times 10^{- 34}\ Js,\ e = 1.6 \times 10^{- 19}\ C.$
$\therefore\ \ \ \ \ \ \ \ \ \ \ \ \ \ m = \frac{6.6 \times 10^{- 34}}{1.6 \times 10^{- 19}} = 4.125 \times 10^{- 15}$