Q$\mathrm{.}4.$ The electron beam in a certain cathode ray tube possesses cylindrical symmetry, and the charge

density is represented by p$,=-0\mathrm{.}1/($p$2+10-8)$ pC$/$m$3$ for $0310$~$4$m$.$

$($a$)$ Find the total charge per meter along the length of the beam; $($b$)$ if the electron velocity is $5107$ m$/$s$,$

and with one ampere defined as $1$C$/$s$,$ find the beam current.

T$107$