$.*$C$12-31$: Two long, straight wires are parallel and $10\mathrm{.}0$ cm apart. One

carries a current of $2\mathrm{.}00$ A$,$ the other a current of $5\mathrm{.}00$ A$.$

$($a$)$ If the two currents flow in opposite directions, what is the magnitude and

direction of the force per unit length that one wire exerts on the other? $($b$)$ What is

the magnitude and direction of the force per unit length if the currents flow in the

same direction?

Answers: a$)5$

$/210$ N$/$mF l $-$

$=$ away from the other wire; b$)5$

$/210$ N$/$mF l $-$

$=$ toward the

other wire