$($a$)$ Explain why we use Copper as a conductor of current. Define $1$ C of charge, $1$ A of current, $1$ Ohm Resistance, $1$ W of power and $1$ I voltage of potential difference.

$[5]$

$($b$)$ If $12\mathrm{.}48{10}^{16}$ electrons pass through a wire in $1\mathrm{.}25$ ms $,$ find the current through the wire. Calculate the voltage drop if the above current converts $10$ Joules of electric energy into heat in $30$ s $.$ Hints: Charge of $1$ electron $=1\mathrm{.}602{10}^{-19}C$; Current$=$Charge$/$Time; Voltage $=$ Energy$/$Charge$]c{m}^2[10]$

$($c$)$ Find the resistance of a $50$ m long copper cable, with cross$-$sectional area $0\mathrm{.}0015c{m}^2$ at room temperature $20C.$ Find the changed value of this resistor and determine its new value when it is heated to heated to $150C.[$Hints: $(T_1+2345)$

$[10]$