NOTA-Self inductance

SELF-INDUCTANCE

1

Arrive on the moon.
TASK 1:

Find the definition of
self-inductance.

2

It is a phenomenon
where a varied
current circuit has an
induced e.m.f in it due
to the variation in its
own magnetic field.

3

4

When switch is closed, there is
current flow through the circuit.
It produces an induced magnetic
field through the current circuit.

5

As the switch is closed, the
current will also increase in
time (0 to maximum).

Thus, the flux which is due
to this current will also
increase in time.

6

When the current in the coil is
increasing, the self-induced e.m.f
produced in the coil will oppose the
current.

This means that the direction of the

induced e.m.f is opposite to the

applied voltage. 7

And the direction of induced
current is opposing the direction
of the current produced by the
battery.

8

Self induced e.m.f is
always proportional to
the time for the rate of
change of the source
current.

9

Self Inductance, L is the
ratio of the self induced
e.m.f to the rate of change
of current in the conductor.

SI unit :

Henry ( H ) or
V s A-1 or
Wb A-1

10

Negative sign : Opposes
the increase in current.

where
L = Self-inductance
= induced e.m.f
= rate of change of SOURCE current

11

Inductance, L depends on
the geometry of the
circuit and other physical
characteristics.

12

Coil

13

Solenoid

where
L : self inductance
N : number of turns
μo: permeability of free space
(4π × 10–7 T m A–1)
A : cross sectional area of the solenoid
l : length of the solenoid
n : number of turns per unit length 14

Thus, the
inductance
will increase.

15

Since

As the conductor is placed, the
inductance is;

or

where
μ : permeability of the material
μr : relative permeability
μ0 : permeability of free spac1e6

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