FARADAY’S LAW OF INDUCTION

• According to Faraday’s rst law of electromagnetic
  induction, whenever the magnetic ux linked with
  a circuit changes, an emf is induced in the circuit.
  e SI unit of induced emf is volt.


• Magnetic Flux : e total number of magnetic eld
  lines crossing through the surface is known as the
  magnetic ux of the any surface held in magnetic
  eld



B.

If a loop enclosing an area A is placed in a magnetic

eld



B,then the magnetic ux through the loop is

φB=⋅∫BdA

 

• According to Faraday’s second law of
  electromagnetic induction, the magnitude of the
  induced emf in a circuit is equal to the time rate of
  magnetic ux through the circuit.

ie

d

dt

..ε

φ

=−

In the case of a closely wound coil of N turns,

change of ux associated with each turn is the same.

∴=−ε

φ

N

d

dt

Lenz’s Law and energy conservation

According to Lenz’s law, the induced current has a

direction such that the magnetic eld due to the current

opposes the change in the magnetic ux that induces

the current. In other words, the polarity of the induced

emf/current is such that it always opposes the change in

magnetic ux which produces the induced emf/current.

Lenz’s law is in accordance with the principle of

conservation of energy.

• Fleming’s Right Hand
  Rule : Fleming’s right
  hand rule also gives us
  the direction of induced
  emf or current, in a
  conductor moving in a
  magnetic eld.
  According to this rule, if we stretch the fore nger,
  central nger and thumb of our right hand in
  mutually perpendicular directions such that fore
  nger points along the direction of the eld and
  thumb is along the direction of motion of the
  conductor, then the central nger would give us the
  direction of induced current or emf. e direction
  of induced current or emf given by Lenz’s law and
  Fleming’s right hand rule is the same.


• Applications of Lenz’s
  Law : When a north
  pole of a bar magnet is
  moved towards a coil,
  the current induced
  in the coil will be in
  anticlockwise direction as shown in the gure.

Magnetic

field

Induced

current

Motion of conductor

S N

F CUS

2019

Class

XII

NEET/JEE

UNIT 4 : ELECTROMAGNETIC INDUCTION AND ALTERNATING CURRENT

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