In an experiment of the photoelectric effect, light from a point source of monochromatic light of way length $3000Å$ is incident on a metal surface. If kinetic energies of photoelectrons range from zero $4\times {10}^{-19}J$, then

$$\begin{gathered} K_{\max }=4\times {10}^{-19}J=\frac{4\times {10}^{-19}}{1.6\times {10}^{-19}}=2.5 \mathrm{eV} \\ \Rightarrow \text{ Stopping potential }=2.5 \mathrm{V} \\ \text{ Since, }{K}_{max}=hc\left(\frac{1}{\lambda }-\frac{1}{{\lambda }_0}\right) \\ \Rightarrow 2.5=\frac{1240}{300}-\frac{1240}{{\lambda }_0} \\ \Rightarrow {\lambda }_0=759 \mathrm{nm}=7590Å \end{gathered}$$

Stopping potential will not change by changing the distance from source. Also reducing the wavelength by half does not double the stopping potential as the work function does not change.

Reducing the distance from the source to half increases the intensity and saturation current four times.