Magnetic Dipole Moment

Formula

Description

The magnetic dipole moment of a current loop measures the strength of the equivalent bar magnet it forms. It equals the number of turns times the current times the enclosed area. The torque a loop feels in an external field is τ = m × B, so the dipole moment sets the torque available in motors, galvanometers, and compass needles.

Variables

• m — Magnetic dipole moment (A·m²)
• N — Number of turns
• I — Loop current (A)
• A — Area enclosed by the loop (m²)

Practical Notes

Torque in an external field is τ = m·B·sinθ, and the loop’s potential energy is −m·B·cosθ. Larger area or more turns gives more torque for the same current.