The work function of copper is $4.7 \mathrm{eV}$. If ultraviolet light of wavelength $312 \mathrm{nm}$ and intensity $1.0 \mathrm{W}{ \mathrm{m}}^{-2}$ is directed on a copper plate, then in the detector

In an experimental observation of the photoelectric effect, the stopping potential was plotted against the incident light frequency as shown in the figure below:

If the work function of the metal is given by ${\varphi }_0$, the angle $\alpha$ is given by

(Here, $h$ and $e$ are Planck's constant and charge of electron respectively).

The slope of graph drawn between stopping potential and frequency of incident light for a given surface will be:-