Tarun places a compass under a straight copper wire and switches the current on
Tarun places a compass under a straight copper wire and switches the current on. The needle turns. He says the compass must be faulty, since copper is not magnetic. Rekha says the flowing current itself is doing it. Who is right?
Who do you think is right? Pick one.
The answer: Rekha is right
Why
Tarun is correct about copper, and that part is worth keeping: a copper wire lying there with no current will not move a compass needle at all, however close you bring it. What he misses is that the wire is no longer just copper once current flows — a current is charge in motion, and moving charge wraps a magnetic field around the wire. The metal is only the road; the magnetism belongs to the traffic. Test: switch the current off and the needle swings back to north, switch it on and it turns again, as many times as you like — the copper never changed, only the flow did. Rekha is right: it is the current that is magnetic, not the wire.
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