·
Magnetic Flux: The magnetic flux f through an area is
defined as f = .
=
BA cos q where q is the angle made by with .

A coil of area in
a
uniform magnetic field


·
·
Faraday's Law: The magnitude of induced e.m.f. in a circuit is directly proportional to the rate
of change of flux through the circuit.
e µ

df


dt

·
·
Lenz's Law: The direction of induced e.m.f. is such that it opposes the cause that produces
it.
\ e = 

df


dt

·
·
Self Induction: The phenomenon of induction of an e.m.f. in a coil due to change in the current flowing
through the same coil.
·
Mutual Induction: The phenomenon of induction of an e.m.f. in a coil due to change in the current flowing in
a neighbouring coil.
·
Induction Coil: It was deviced by
Ruhmkorff in 1851. This is a device by which a
direct current at low voltage is converted into intermittent direct current
at high voltage.
·
Earth Coil: It is a device which is used to measure the
vertical and horizontal component of the earth's magnetic field and the angle
of dip.
·
Phase Difference: The phase difference between two
alternating quantities indicates the lead or lag of one quantity with respect
to the other.
·
R.M.S. Value of an A.C.: The root mean square
(r.m.s.) value of an
alternating current is the value of the direct current which produces the
same amount of heat in the same time in the same conductor.
·
Capacitive Reactance:

The quantity X_{C} =

1

is called the
capacitive reactance of a capacitor and is a measure of


2p fC

·
the opposition offered by the capacitor
to the flow of the alternating current.
·
Inductive Reactance: The quantity X_{L} = 2pfL is called the
inductive reactance and is a measure of the opposition offered by an inductor
to the flow of the alternating current.
·
Impedance of an LCR Series Circuit: The total opposition
offered by a circuit containing an inductance L, a capacitor C, and a
resistance R and an alternating source is given by Z = .
The quantity Z is known as the impedance of the circuit.
·
Resonant Circuits:
(a) Series Resonance: An LCR series resonant circuit is shown below.
·
In this circuit, the reactive component of the opposition offered to the ac
current becomes zero at a certain frequency called the resonant frequency.
Therefore, the current in the circuit is maximum at
this frequency.
f_{0} =

1


2p

·
(b) Parallel Resonance:
·
When frequency f_{0} of a.c. source is such that =
w_{0}C, the line current
in the circuit becomes minimum (zero). An oscillatory current flows between L
and C. This phenomenon is known as parallel resonance. Resonance frequency is
given by
f_{0} =

1


2p

·
