Page 473 - Basic Electrical Engineering

Figure 5.2 (a) Magnetic field around a current-carrying conductor; (b) two conductors placed side by
side carrying current in opposite directions; (c) two conductors placed side by side carrying current in
the same direction

When a conductor is wound in the form of a coil, a resultant magnetic field
is established around it. After passing a direct current, if a magnetic needle is
brought near the coil, it will be observed that the coil has a North pole and a

South pole. The magnetic field produced by a current-carrying coil, the
magnetic field around it, and the positions of the North and South poles have

been shown in Fig. 5.3.
The strength of a magnetic field is expressed in terms of the number of
8
flux lines, f and is measured in Webers, where 1 Wb = 10 lines.

5.1.2 Magnetic Flux Density

Magnetic flux density, i.e., flux per unit area is denoted by B. If A is the area

through which the flux lines emanate, i.e., come out, the flux density is given