ElectroMagnetic Induction Revision Notes - IIT JEE/NEET Preparation | Nucleon

ElectroMagnetic Induction

• FARADAYS LAWS OF ELECTROMAGNETIC INDUCTION
• When magnetic flux passing through a loop changes with time or magnetic lines of
force are cut by a conducting wire then an emf is produced in the loop or in that
wire. This emf is called induced emf.

• LENZS LAW (CONSERVATION OF ENERGY PRINCIPLE)
• According to this law, emf will be induced in such a way that it will oppose the cause which has
produced it. Figure shows a magnet approaching a ring with its north pole towards the ring

• MOTIONAL EMF
• We can find emf induced in a moving rod by considering the number
of lines cut by it per sec assuming there are ‘B’ lines per unit
area. Thus when a rod of length moves with velocity v in a magnetic
field B, as shown, it will sweep area per unit time equal to v
and hence it

• EXPLANATION OF EMF INDUCED IN ROD ON THE BASIS OF MAGNETIC FORCE
• EXPLANATION OF EMF INDUCED IN ROD ON THE BASIS OF MAGNETIC FORCE

• INDUCED EMF DUE TO ROTATION
• ROTATION OF THE ROD
Consider a conducting rod of length l rotating in a uniform magnetic field.

• EMF INDUCED IN A ROTATING DISC
• Consider a disc of radius r rotating in a magnetic field B.
Consider an element dx at a distance x form the centre. This element is moving with

• FIXED LOOP IN A VARYING MAGNETIC FIELD
• Now consider a circular loop, at rest in a varying magnetic field. Suppose the magnetic field is
directed inside the page and it is increasing in magnitude. The emf induced in the loop will be

• SELF INDUCTION
• Self induction is induction of emf in a coil due to its own current change.Total flux N?
passing through a coil due to its own current is proportional to the current and is given as N
L i where L is called coefficient of self induction or inductance.The inductance L is purely

• SELF INDUCTANCE OF SOLENOID
• Let the volume of the solenoid be V , the number of turns per unit length be n.
Let a current I be flowing in the solenoid.Magnetic field in the solenoid is given as

• INDUCTOR
• If current i through the inductor is increasing the induced emf will oppose the increase in
current and hence will be opposite to the current.If current i through the inductor is decreasing
the induced emf will oppose the decrease in current and hence will be in the direction of the
current.

• ENERGY STORED IN AN INDUCTOR
• If current in an inductor at an instant is i and is increasing at the rate di/dt,the induced emf
will oppose the current . Its behaviour is shown in the figure.

• GROWTH OF CURRENT IN SERIES R–L CIRCUIT
• Figure shows a circuit consisting of a cell, an inductor L and a resistor R ,connected in series. Let the
switch S be closed at t=0.Suppose at an instant current in the circuit be i which is increasing at the rate
di/dt.

• DECAY OF CURRENT IN THE CIRCUIT CONTAINING RESISTOR AND INDUCTOR
• DECAY OF CURRENT IN THE CIRCUIT CONTAINING
RESISTOR AND INDUCTOR

• MUTUAL INDUCTANCE
• Consider two arbitrary conducting loops 1 and 2. Suppose that ?1 is the instantaneous current flowing around
loop 1. This current generates a magnetic field B1 which links the second circuit, giving rise to a magnetic flux ?2
through that circuit. If the current ?1doubles, then the magnetic field B1 doubles in strength at all points in space,
so the magnetic flux ?2 through the second circuit also doubles. Furthermore, it is obvious that the flux through
the second circuit is zero whenever the current flowing around the first circuit is zero. It follows that the flux ?2

• TRANSFORMER
• A transformer changes an alternating potential difference from one value to another of greater or
smaller value using the principle of mutual induction .Two coils called the primary and secondary
windings,which are not connected to one another in any way , are wound on a complete soft iron
core.When an alternating voltag

• ENERGY LOSSES IN TRANSFORMER
• Although transformers are very efficient devices, small energy losses do occur in them due to four main causes.
1. RESISTANCE OF THE WINDINGS

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