DIRECTION OF INDUCED EMF

The direction of induced emf and hence current in a conductor or coil can be determined by either of the following two methods:

1. Fleming’s Right-hand Rule: This rule is applied to determine the direction of induced emf in a conductor moving across the field and is stated as‘Stretch first finger, second finger, and thumb of your right-hand mutually perpendicular to each other. If first finger indicates the direction of magnetic field and thumb indicates the direction of motion of conductor, then second finger will indicate the direction of induced emf in the conductor.’Its illustration is shown in Figure 5.27.
2. Lenz’s Law: This law is more suitably applied to determine the direction of induced emf in a coil or circuit when flux linking with it changes. It is stated as ‘In effect, electromagnetically induced emf and hence current flows in a coil or circuit in such a direction that the magnetic field set up by it always opposes the very cause which produces it.’

When N-pole of a bar magnet is taken near to the coil, as shown in Figure 5.28 (a), an emf is induced in the coil, and hence, current flows through it in such a direction that side ‘B’ of the coil attains North polarity that opposes the movement of the bar magnet. While N-pole of the bar magnet is taken away from the coil, as shown in Figure 5.28 (b), the direction of emf induced in the coil is reversed and side ‘B’ of the coil attains South polarity that again opposes the movement of the bar magnet.