ELECTROMAGNETIC INDUCTION
| Electromagnetic induction | Experiments of Faraday and Henry |
| Magnetic flux | |
| Faraday’s law | Statement and explanation |
| Induced EMF | |
| Lenz’s law | Statement |
| explanation and its significance as conservation of energy | |
| Motional emf | |
| Eddy currents | |
| Inductance | Mutual induction |
| Self inductance | |
| Energy stored in the coil. | |
| Ac generator | Working |
| Derivation of instantaneous emf in an ac generator | |
| Hydro – electric generators | |
| Numericals | Concept based problems |
Magnetic flux:
The magnetic flux through a surface of area A placed in a uniform magnetic field B is defined as,
ΦB = B.A = BA cos θ
where θ is the angle between B and A
ΦB = B.A = BA cos θ
where θ is the angle between B and A
Faraday’s laws of induction:
Faraday’s laws of induction imply that the emf induced in a coil of N turns is directly related to the rate of change of flux through it,
Here ΦΒ is the flux linked with one turn of the coil. If the circuit is closed, a current I = ε/R is set up in it, where R is the resistance of the circuit.
Here ΦΒ is the flux linked with one turn of the coil. If the circuit is closed, a current I = ε/R is set up in it, where R is the resistance of the circuit.
Lenz’s law:
Lenz’s law states that the polarity of the induced emf is such that it tends to produce a current which opposes the change in magnetic flux that produces it. The negative sign in the expression for Faraday’s law indicates this fact.
Induced emf:
When a metal rod of length l is placed normal to a uniform magnetic field B and moved with a velocity v perpendicular to the field, the induced emf (called motional emf) across its ends is,
ε = Blv
ε = Blv
Inductance:
Inductance is the ratio of the flux-linkage to current. It is equal to NΦ/I.
Mutual inductance:
A changing current in a coil (coil 2) can induce an emf in a nearby coil (coil 1).
This relation is given by,
The quantity M12 is called mutual inductance of coil 1 with respect to coil 2. One can similarly define M21. There exists a general equality,
M12 = M21
This relation is given by,
The quantity M12 is called mutual inductance of coil 1 with respect to coil 2. One can similarly define M21. There exists a general equality,
M12 = M21
Self-induced emf:
When a current in a coil changes, it induces a back emf in the same coil. The self-induced emf is given by,
L is the self-inductance of the coil. It is a measure of the inertia of the coil against the change of current through it.
L is the self-inductance of the coil. It is a measure of the inertia of the coil against the change of current through it.
The self-inductance of a long solenoid, the core of which consists of a magnetic material of relative permeability µr , is given by
L = µr µ0 n2 Al
where A is the area of cross-section of the solenoid, l its length n is the number of turns per unit length.
L = µr µ0 n2 Al
where A is the area of cross-section of the solenoid, l its length n is the number of turns per unit length.