. M AGNETIC F ORCE . . Sources and fields Before we introduce the concept of a magnetic field B , we shall recapitulate what we have learnt in Chapter about the electric field E.
We have seen that the interaction between two charges can be considered in two stages. The charge Q, the source of the field, produces an electric field E , where FIGURE . The magnetic field due to a straight long current-carrying wire. The wire is perpendicular to the plane of the paper.
A ring of compass needles surrounds the wire. The orientation of the needles is shown when (a) the current emerges out of the plane of the paper, (b) the current moves into the plane of the paper. (c) The arrangement of iron filings around the wire. The darkened ends of the needle represent north poles.
The effect of the earth’s magnetic field is neglected. Hans Christian Oersted ( – ) Danish physicist and chemist, professor at Copenhagen. He observed that a compass needle suffers a deflection when placed near a wire carrying an electric current. This discovery gave the first empirical evidence of a connection between electric and magnetic phenomena.