OBSERVATION

Lenz’s law states that the direction of flow of current due to the induced emf is such as to oppose the change causing it. According to the report, many candidates described this (rather incorrectly) in terms of the ‘direction of the induced emf’. Faraday’s Law of electromagnetic induction states that when there is relative motion between a conductor and the magnetic flux lining it, an e.m.f. is induced across in the terminals of the conductor; and that the magnitude of the induced e.m.f. is directly proportional to rate at which this flux linkage changes. It was reported that virtually all the candidates could list three applications of electromagnetic induction.

The expected responses were:

• (i)Lenz’s law states that the direction of induced emf is always such as to oppose the

change producing it.
(ii)Faraday’s law

• Whenever there is a relative motion between a conductor and a magnetic field such that the conductor cuts the magnetic field, an emf is induced in theconductor.
• Any change in magnetic flux in a conductor induces an emf in the conductor
• The magnitude of the induced emf is directly proportional to the rate of change of the flux.      

• Applications of electromagnetic induction
• Loudspeaker
• Electric bell
• buzzer
• moving coil instrument
• earphone
• microphone
• generators
• transformer
• solenoid