Given the surface charge density, s $=2$C$/$m$2,$ existing in the region $<0\mathrm{.}2$ m$,$ z $=0,$ find E at $($a$)$ PA$($ $=0,$z $=0\mathrm{.}5)$; $($b$)$ PB$($ $=0,$z $=0\mathrm{.}5).$ Show that $($c$)$ the field along the z axis reduces to that of an infinite sheet charge at small values of z; $($d$)$ the z axis field reduces to that of a point charge at large values of z