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Asked in GSEB Board July 2021 · Force between parallel currents
Given: two long parallel wires, first with their currents the same way, then opposite ways.
Idea: each wire sits in the field of the other and feels ⃗F=Iℓ⃗×⃗B.
Same direction: the field of wire 1 at wire 2 is perpendicular to the plane of the two, and Iℓ⃗×⃗B then points from wire 2 towards wire 1 — they attract.
Opposite directions: reversing one current reverses that force, so the wires are pushed apart — they repel.
So parallel currents attract and antiparallel currents repel.
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