a wire is $3\mathrm{.}75$m long and $7\mathrm{.}84$mm in diameter has a resistance of $17\mathrm{.}2$micro ohms. a potential difference if $23\mathrm{.}8$V is applied between the ends. $($a$)$ what is the current in amperes in the wire? $($b$)$ what is the magnitude of the current density? $($c$)$ calculate the resistivity of the material of which the wire is made