what is magnetic field?

In our previous chapter of electricity, we learned about electric circuits, and also started about the heating effect of electric current. Before we proceed to this lesson, let’s perform a small experiment just take a magnetic compass and place it over a current carrying wire.

What do we observe?

We see a deflection in the magnetic compass. What does this mean? A magnetic compass shows deflection only in the presence of a magnetic field. In the experiment we just did, we saw deflection in our compass. This means, that the current carrying wire produces a magnetic field.

Thus, there is a link between electricity and magnetism. The experiment we did was actually done by Oersted in the 19th century, where he established a link between electricity and magnetism. We all must have heard about magnets, and in our childhood, we also must have played with magnets. In this lesson, we study the properties of a bar magnet.

If I freely suspend a bar magnet, the end which points towards the North is the North seeking end and the end which point towards the South is the South seeking end. Therefore, a bar magnet has a North Pole and a South Pole. In our previous classes, we have learnt that like poles repel each other and unlike poles attract each other.

Let us do one more experiment. Take a bar magnet and fix it on a sheet of paper. Then sprinkle iron filings all around the magnet; and gently tap the paper.

What do I observe?

I observe the iron filings which were randomly spread around the magnet, have aligned themselves into a specific pattern. This means, a magnet exerts an influence on its surrounding region. The iron filings must have experience a force, that has arranged them in such a pattern.

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The lines along which the iron filings are arranged or aligned is nothing but the magnetic field lines of a bar magnet. The region surrounding the magnet, in which the force of the magnet can be felt, is the extent of the magnetic field for that particular magnet. Magnetic field is a vector quantity. That is, it has both magnitude and direction.

By convention we assume that magnetic field lines originate from the North Pole and merge in the South Pole but inside the magnet, magnetic field lines are directed from the South Pole to the North Pole. Thus, we can see that magnetic field lines form a closed curve.

The relative strength of a magnetic field is estimated, by how close the field lines are to each other. If the field lines are really close, it indicates a strong magnetic field. On the other hand, if the field lines are far apart, it indicates a weaker field. Also, magnetic field lines can never intersect each other. If they do intersect, and we keep a magnetic compass at that point we would get two different directions, which is not possible.

So, let us quickly recap what we learned in this lesson. We saw that the current carrying wire produces a magnetic field. We got an idea about the magnetic field of a bar magnet and we also studied the properties of magnetic field lines.

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