Page 471 - Basic Electrical Engineering

Figure 5.1 (a) and (b) permanent magnets; (c) and (d) electromagnets

Fig. 5.1 (a) shows a bar-type permanent magnet, while Fig. 5.1 (b) shows a

horse-shoe-type permanent magnet. Fig. 5.1 (c) and (d) are electromagnets. It
should be noticed that the North pole is the one wherefrom the magnetic lines

of force come out of the magnet body and the South pole is the one where the
lines of force enter the magnet body. In Fig. 5.1 (d) has been shown a solid
cylindrical core around which a coil of two turns have been wound. The

direction of currents at the two sides of a coil have been shown by crosses
and dots. A cross indicates current entering and a dot indicates current

coming out. The direction of flux around the coil sides have been determined
by applying the cork screw rule. After showing the lines of force and their

directions, we identify the portion of the core from where the flux lines leave
the magnet body and call that area as the North pole.