Moving Charges and Magnetism — Important Questions

It deflects

A current-carrying wire produces a magnetic field, which exerts a force on the magnetic compass needle, causing it to deflect.

Current and number of turns

The magnetic field at the center of a circular coil is given by \( B = rac{\mu_0 nI}{2r} \), so it depends on current (I) and number of turns (n).

1/r

The magnetic field due to a long straight current-carrying wire is \( B = rac{\mu_0 I}{2\pi r} \), which is inversely proportional to the distance (r).

Current enclosed

Ampere’s circuital law states that the line integral of B around a closed loop is equal to μ₀ times the current enclosed by the loop.