Magnetic Dipole Moment

The magnetic properties of objects have been known to humans for a long time. Even though at first, humankind did not understand why magnets behave the way they do, their functions and utilities have been used by people for a long time. Magnets and the magnetic properties of the Earth had helped ships navigate vast oceans long before the existence of advanced technology.

Understanding the magnetic dipole moments and properties is essential to understand how a magnet works. Therefore, explained in the article below is information relevant to understanding how a magnet works.

Many objects exhibit magnetic properties, including elementary particles like electrons, molecules, a loop of electrical current, planets, moons etc. The magnetic movements of these objects are known as a system's magnetic dipole moment, which refers to a pair of equal and oppositely charged or magnetic poles separated by a small distance.

Various Properties of a Magnet

The torque experienced by an object in a specific magnetic field is known as its magnetic dipole moment. In a magnetic field that is unchanged, an object with larger magnetic moments will create larger torques. The direction of the torque, along with its strength, depends on the magnitude of the magnetic moment and its placement when compared to the direction of the magnetic field. Since magnitude and direction play a role, the magnetic moment is considered a vector quantity in physics. Inside a magnet, the direction of the magnetic moment is from the south pole to the north.

The magnetic moment can be understood as a vector quantity that connects the aligning torque on an object from an external magnetic field to the vector quantity in the field.

It is mathematically represented as:

ταυ = m X B

The torque acting on the dipole is represented by “ταυ” in the above equation, while B represents the external magnetic field. The ‘m’ in the equation represents the magnetic moment.

This definition is based on the concept of measuring the magnetic moment of a sample that is not known. In the case of a current loop, this definition represents the quantity of the magnetic dipole moment connected to the sum of the current multiplied by the region of the loop. Thus, with any known macroscopic current sharing, this definition can be applied.

The concept of Magnetic dipole

As explained above, the magnetic dipole is the magnitude that highlights the strength and magnetic orientation of any magnet or object with a magnetic field. Or in other words, a magnetic dipole refers to the magnetic north and south pole separated by a small distance.

The current loop and magnetic poles are the two types of the dipole that predict the same result for a magnetic field that is far away from its source. However, within a source, these two dipoles do not give the same predictions. Within a current loop, the magnetic field between two poles is in the same direction. In comparison, the magnetic field between the two poles, points from the negative to the positive charge and thus in the opposite direction of the magnetic moment.

The theory of magnetic dipole goes beyond the modelling of particles that are atomically sized and can also be used to understand larger objects and their collections. For example, a compass needle or an MRI scanner or even the Earth exhibits the properties of an enormous dipole.

When one looks at a small current loop, one can see it behaving like a small magnet. This is technically known as a magnetic dipole.

The strength of the magnet or the magnetic dipole moment is represented by the equation:

m = NIA

"m" represents the magnetic dipole moment, and the units given are Ampere meter square (Am²).

The direction of the magnetic dipole quantity, which is a vector in nature, can be figured out by anybody using the right-hand thumb rule. The direction is perpendicularly opposite to the surface side, which is sealed with an anticlockwise route emulating positive charge flow.

Using the SI system, the designated unit for the dipole moment is ampere-square meter. But, in the centimetre - the second system, it is erg, a unit of energy per gauss which is a unit of magnetic flux density.

Note: One ampere-square meter is the same as one thousand ergs per gauss.

The magnetic dipole moment of a magnet is important to understand while deciphering the physical world around us.