What Are Magnetic Poles

∟What Are Magnetic Poles

This section provides a quick introduction of magnetic poles, where magnetic influences are much higher than other regions in magnetic fields.

What Are Magnetic Poles? A Magnetic Pole is an region where the magnetic field has much higher magnetic influence (higher concentration of magnetic lines) than neighboring regions.

Magnetic poles always come in pairs. The two poles in a pole pair are connected by magnetic lines. The magnetic influence in one pole has reverse direction than the other pole in a pole pair.

For example, a magnetic bar has one pair of poles located each end of the bar.

Earth is also a magnet with one pair of poles located near the geographic north point and south point.

What Is Compass? A compass is a magnet needle with a pair of poles at two ends labeled as north and south using Earth's magnetic field as a reference. This can be done in 2 steps:

Place a compass in Earth's magnetic field. The magnet needle in the compass will turn and align itself with the magnetic line under the magnetic influence of Earth.
Label the needle end that points to the geographic north of Earth as north colored red, and the other end as south colored blue.

The picture below from sos.noaa.gov/catalog/datasets/earths-magnetic-lines/ shows north ends (in red) of compass needles pointing the Earth's magnetic north pole. Lines in the picture are longitude lines, not magnetic lines. Earth's magnetic north pole is slightly dis-located from the Earth's geographic north. This is why compass needles are not exactly aligned to longitude lines.

Compass Needle North Pointing to Earth North

What Is the Direction of Magnetic Line? The direction of a magnetic line is defined to follow the north direction of the compass needle placed on the line. This is shown in a diagram from hyperphysics.phy-astr.gsu.edu/hbase/magnetic/elemag.html:

Direction of Magnetic Line Defined by Compass Needle

How to Differentiate North Pole from South Pole? We can label the two poles in a pole pair as north pole and south pole, and differentiate them from each other by following directions of magnetic lines in the outside region of the magnetic field.

The pole where outside magnetic lines are going into is labeled as the south pole, which is also pointed by the north ends of compass needles.

The pole where outside magnetic lines are coming out is labeled as the north pole, which is also pointed by the south ends of compass needles.

Remember that some portions of magnetic lines are located inside the the magnetic object or device that creates the magnetic field. But we are not using those portions to define north pole and south pole. The above diagram shows north pole and south pole are defined on a magnetic bar.

Also note that by applying this definition to Earth's magnetic field, the magnetic north pole is technically at the geographic south; and the magnetic south pole is technically at the geographic north. This confusion is a result of how we use Earth's magnetic field as a reference to define compass needle poles.