Along a straight stretch of lamp flex the two copper conductors run parallel

PHYSICS · Multi-part · Fermi University Physics · Electricity, Magnetism & Electromagnetism · Magnetostatics · Magnetostatics

Electricity, Magnetism and Electromagnetism, Ch The Biot-Savart law and the fields of steady currents

Problem

Along a straight stretch of lamp flex the two copper conductors run parallel,

3.0\,\mathrm{mm}

apart centre to centre, over a length of

1.2\,\mathrm{m}

. Each carries a steady current of

8.0\,\mathrm{A}

, one going to the lamp and the other returning, so the two currents are in opposite directions. Treat each conductor as a long straight thin wire, and ignore the Earth's field and the fields of the rest of the circuit. A student argues: "Opposite charges attract, so opposite currents must attract too; the conductors are squeezed together." ((a)) Find the magnitude of the field of one conductor at the position of the other. ((b)) Find the magnitude of the magnetic force on the

1.2\,\mathrm{m}

stretch of one conductor, and state whether the conductors attract or repel. Say where this argument goes wrong.

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