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