south pole
The negative pole of a magnetic dipole that seeks geographic south.
south pole: the magnet end that points toward Earth's magnetic north
In electrical engineering, the south pole of a magnet is the end of a permanent magnet or electromagnet that is attracted toward the geographic north pole of the Earth. This can be confusing: the south pole of a magnet actually points north geographically because the Earth's magnetic field itself has its north pole in the southern hemisphere. A magnetic dipole has two poles, and they are conventionally named after the geographic direction toward which they are attracted.
In motors and generators, the south pole forms half of the magnetic circuit. Rotating machinery uses alternating south and north poles arranged around a rotor or stator to create the rotating magnetic field that drives torque. The spacing, strength, and number of poles determine the motor's speed, efficiency, and torque characteristics. A four-pole motor, for instance, has two south poles and two north poles arranged alternately around the circumference.
Identification and measurement
The south pole of a magnet can be identified using a compass needle, which orients with its north-seeking end pointing toward a magnet's south pole. Strength is measured in Tesla or Gauss, using a gaussmeter or Hall effect sensor. Industrial magnets used in electric machines typically range from 0.5 to 2 Tesla at the pole face, depending on the application and magnet material, whether ferrite, NdFeB, or older alnico types.
Problems arise when magnetic poles degrade or become uneven. Demagnetization from heat, mechanical shock, or opposing fields weakens the pole's attractive force. Asymmetric pole strength causes vibration and efficiency loss in rotating equipment. In permanent magnet synchronous motors, pole imbalance results in cogging torque and acoustic noise at running speed.
The terminology comes directly from physics: poles are the regions of concentrated magnetic force, named to parallel the Earth's own magnetic poles. Every magnet has both poles; there is no isolated south pole. In power systems and switchgear, beware of confusion with the term south pole used informally to mean the negative terminal or ground reference in DC circuits, which is different from the magnetic pole concept.