Whenever the magnetic flux linked with an electric circuit changes , an emf is induced in the circuit . This phenomenon is called electromagnetic induction .
Faraday ’ s Laws of Electromagnetic Induction
( i ) Whenever the magnetic flux linked with a circuit changes , an induced emf is produced in it . ( ii ) The induced emf lasts so long as the change in magnetic flux continues .
( iii ) The magnitude of induced emf is directly proportional to the rate of change in magnetic flux , i . e .,
E ∝ dφ / dt ⇒ E = – dφ / dt where constant of proportionality is one and negative sign indicates Lenz ’ s law . Here , flux = NBA cos θ , SI unit of φ = weber , CGS unit of φ = maxwell , 1 weber = 10 8 maxwell , Dimensional formula of magnetic flux [ φ ] = [ ML 2 T -2 A -2 ]
Lenz ’ s law
The direction of induced emf or induced current is always in such a way that it opposes the cause due to which it is produced .
Lenz ’ s law is in accordance with the conservation of energy .
Note To apply Lenz ’ s law , you can remember RIN or ® In ( when the loop lies on the plane of paper )
( i ) RIN In RIN , R stands for right , I stands for increasing and N for north pole ( anticlockwise ). It means , if a loop is placed on the right side of a straight current carrying conductor and the current in the conductor is increasing , then induced current in the loop is anticlockwise
( ii ) ® IN In ® IN suppose the magnetic field in the loop is perpendicular to paper inwards ® and this field
is increasing , then induced current in the loop is anticlockwise