$($a$)($I$)$ State Amperes law for the magnitude of the magnetic field produced by a long current carrying wire. $($II$)$ Explain how we tell the direction of the magnetic field in $($I$).$

$1,2$

$($b$)$Two very long horizontal parallel current carrying wires A and $B$ are $5\mathrm{.}00$ cm apart with wire $B$ to the right of wire $A.$ The current in wire $A$ is $25$A while that of $B$ is $10$ A $.$ An observer is standing under the wires and finds that the current is in the forward direction. Relative to the observer, find the magnitede and direction of the magnetic field at the point $C$ which is at the same height as the wires and where point $C$ is

i$.$ midway between the wires,

ii$.2\mathrm{.}50$ cm to the right of wire $B.$

$[5,4]$