Page 54 - Basic Electrical Engineering

most of the electrical machines and devices have been developed utilizing the
observations and discoveries made as mentioned above.

1.9.2 Magnetic Field Around a Current-carrying Conductor

In Fig. 1.3 is shown a conductor carrying a current, I. Lines of force are
established around the conductor on a perpendicular plane. In Fig.1.3 (a)

magnetic field around a long conductor has been shown. The lines of force
are established on a perpendicular plane. In Fig.1.3 (b) and (c), the cross-
sectional views of a current-carrying conductor have been shown. The cross

at the centre of the conductor indicates that current is entering the conductor
which is placed perpendicular to the plane of the paper. The lines of force in

the form of concentric circles are on the plane of the paper. The direction of
current through the conductor is reversed in Fig.1.3 (c). The dot at the centre

of the conductor indicates that the current is coming towards the observer.
The direction of the lines force around the conductor also get reversed.

The direction of flux lines around a current-carrying conductor is
determined by applying the cork screw rule which is stated below.

Figure 1.3 (a) A long current-carrying conductor; (b) cross-sectional view of a conductor with flux
around it; (c) cross-sectional view of the conductor with the direction of current reversed; (d) resultant
magnetic field produced by two current-carrying conductors

Cork Screw Rule: Consider a right hand screw held on one end of a
current-carrying conductor and is rotated in the clockwise direction. If the

advancement of the screw indicates the direction of current, the direction in