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# Five long wires $A,B,C,D$ and $E$ each carrying current I are arranged to form edges of a pentagonal prism as shown in figure. Each carries current out of the plane of paper . What if current in one of the wires (say) A is reversed ?

$\begin{array}{1 1}\frac{\mu_0}{4 \pi} .\frac{I}{R} \text{ acting perpendicular to OA towards right} \\ \frac{\mu_0}{4 \pi} .\frac{I}{R} \text{ acting perpendicular to AO towards right} \\ \frac{\mu_0}{4 \pi} .\frac{I}{R} \text{ acting perpendicular to OA towards left} \\ \frac{\mu_0}{4 \pi} .\frac{I}{R} \text{ acting perpendicular to AO towards left} \end{array}$

magnetic field induced due to wire $A+$ magnetic field induction due to wires $B,C,D$ and $E$
=>$\frac{\mu_0}{4 \pi} .\frac{I}{R} \text{ acting perpendicular to AO towards left}$
$+ \frac{\mu_0}{4 \pi} .\frac{I}{R} \text{ acting perpendicular to AO towards left}$
$\qquad= \large\frac{\mu_0}{4 \pi} .\frac{2I}{R}$
$\qquad=\frac{\mu_0}{ \pi} .\frac{I}{R}$acting perpendicular to AO towards left
Answer : $\frac{\mu_0}{4 \pi} .\frac{I}{R} \text{ acting perpendicular to AO towards left}$