2018-10-01_Physics_For_You

When a north pole of bar
magnet is moved away
from the coil, the current
induced in the coil will be
in clockwise direction as
shown in the gure.
When a current carrying coil is moved towards a
stationary coil, the direction of current induced in
stationary coil is as shown in gure.

(Stationary)

When a current carrying coil is moved away from a
stationary coil, the direction of current induced in
stationary coil is as shown in gure.

(Stationary)

When two coils A and B are arranged as shown in gure,
then on pressing K, current in A increases in clockwise
direction. erefore, induced current in B will be in
anticlockwise direction.

B

A

K

However, when key K is released, current in A decreases
in clockwise direction. erefore, induced current in B
will be in clockwise direction.
When current in a straight conductor AB is increased,
induced current in loop will be in clockwise direction
as shown in the gure. If current in AB is decreasing,
the induced current in the loop will be in anticlockwise
direction.

Current

A B

MOTIONAL EMF

If a conductor is moving with velocity v in a magnetic
eld, electrons inside it experience a force

  

Fe=×()vB

S N

and accumulate at the end of the conductor. Very soon,

an electric eld is established. Eventually component of

magnetic force along the conductor length is balanced

by the electric eld force and the driing of electorns

stops and an emf is established.

Now, ε=−⋅=×∫∫ ⋅

    

Edlv()Bdl

is is general expression for induced emf in a conducting

wire. If 



vB, and



lare mutually perpendicular to each

other then, H = Bvl.

Motional emf in Loop

If a conducting rod moves on two parallel conducting

rails then an emf is induced whose magnitude is

|H| = Blv and direction is given by Fleming’s right hand

rule. Inducedcurrent||

|

I

R

Blv

R

=

|

=

ε

Rotational emf

If a conducting rod of length l rotates about an axis

passing through one of its ends (that end may be xed)

with an angular velocity Z in a plane perpendicular

to the magnetic eld



B. en an induced emf is set

up between ends of rod whose magnitude is given by

||εω=

1

2

Bl^2

Eddy Currents

e current induced in bulk pieces of conductors when

the magnetic ux linked with the conductor changes

are known as Eddy currents.

INDUCTANCE

An electric current can be induced in a coil by ux

change produced by another coil in its vicinity or ux

change produced by the same coil. e ux through a

coil is proportional to the current i.e. φ v I

For a closely wound coil of N turns, Nφ v I

or φ=

LI

N

where L is the constant of proportionality called

inductance. SI unit of inductance is Tm^2 A–1 or

henry (H) and its dimensional formula is [ML^2 T–2A–2].

Self Inductance

Whenever the current passing through a coil or circuit

changes, the magnetic ux linked with it will also

change. As a result of this, an emf is induced in the coil

or the circuit which opposes the change that causes it.