What are Magnetic Fields: How to Plot and Measure It


A magnetic field is a region (area) around a magnet or a magnetic material within which the force of magnetism can be felt. Any other magnetic substance that comes into this region will either be attracted or repelled. You can usually see the field represented diagrammatically by curved lines that radiate from the two poles of the magnet, the inner ones joining the two poles. If you or your child is struggling with this concept in school, get enrolled in a Physics tuition to get a good grasp of the concept. In this article, we give an introduction of what magnetic fields are and how do they work.

How to plot magnetic fields

There are two different ways that are typically used to illustrate magnetic fields.

The first is by plotting a vector field. Mathematically, a magnetic field is described as a vector field. A vector, as you may be aware, is a quantity that has both direction and magnitude. It is represented by an arrow pointing in the direction of the quantity and having a length that is proportional to the magnitude of the quantity.

The vector field of a magnet can be plotted as a set of multiple vectors drawn on a grid, with each vector pointing in the direction that a compass would point and having the length proportional to the strength of the magnetic force.

The second method is to represent the vector field using field lines. This is the easier and more frequently used (especially in schools) method as it dispenses of the grid pattern and allows you to use smooth lines to connect the vectors. You can draw as many lines as you want.

The field lines have some properties that give us some good ideas about magnetic fields. They never cross. They bunch together in regions where the magnetic field has the highest strength. They don’t begin or end anywhere; rather, they always make closed loops. The direction of the magnetic field is usually shown by drawing arrowheads along the lines.

How to measure magnetic fields

Since a magnetic field is a vector quantity, there are two quantities we need to measure: strength and direction.

The direction of a magnetic field is easy to measure. The usual way is to use a magnetic compass, which lines up with the field. Thus, we can easily know the direction. The magnetic compass has been used for hundreds of navigation as they show the direction accurately by using the earth’s magnetic field.

The strength of a magnetic field is measured using a magnetometer. Most magnetometers work by measuring the force an electron experiences as it moves through a magnetic field. The SI unit for measuring magnetic field strength is Tesla (named after Nikola Tesla). A Tesla is a force needed to move a charge due to a magnetic field. A small refrigerator magnet has a magnetic strength of 0.0001 Tesla.

The origin of magnetic fields

You probably know that magnetism is an aspect of the electromagnetic force, which is one of the four fundamental forces that occur in nature. A magnetic field is the result of electrical charges in motion inside a magnet or a magnetic substance. The more charges there are in motion, the greater the strength of the magnetic field. This means that we can create a magnetic field by passing an electric current through a wire. You will notice that the higher the flow of current, the stronger the magnetic field will become.

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