Two parallel wires in free space are $10\, cm$ apart and each carries a current of $10\, A$ in the same direction. The force one wire exerts on the other per metre of length is
A$2 \times {10^{ - 4}}\,N$, attractive
B$2 \times {10^{ - 4}}\,N$, repulsive
C$2 \times {10^{ - 7}}\,N$, attractive
D$2 \times {10^{ - 7}}\,N$, repulsive
AIPMT 1997, Medium
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A$2 \times {10^{ - 4}}\,N$, attractive
a (a) $F = \frac{{{\mu _0}}}{{4\pi }}\frac{{2{i_1}{i_2}}}{a} = {10^{ - 7}} \times \frac{{2 \times 10 \times 10}}{{0.1}} = 2 \times {10^{ - 4}}\,N$
Direction of current is same, so force is attractive.
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