$($a$)$ Outline how the apparatus in Fig $4\mathrm{.}1$ can be used to determine the stopping potential of metal $E.$

$[5]$

$N_0$

$4\mathrm{.}1$

$($b$)$ Determine the maximum kinetic energy of photoelectrons ejected from calcium with a work function of $2\mathrm{.}71$ eV by an electromagnetic radiation of wavelength $350$nm$.$

$[6]$