Page 137 - Physics - XII

Apparatus and Materials Required

A coil of large number of turns, an A.C. ammeter of suitable range, an A.C. source of adjustable frequency,
an electric bulb (6 volt), one-way key, a soft iron rod, connecting wires, rheostat, and sand paper

Principle/Theory
Self-induction is the property of a coil by virtue of which the coil opposes any change in the strength of
current fl owing through it by inducing an e.m.f. in itself.

µµ NA
2
L = 0 r
l
Where μ is the absolute magnetic permeability of free space/air
0
μ r is the relative permeability of the magnetic material

N is total number of turns in the solenoid
A is the area of cross-section of the solenoid
l is the length of solenoid

Thus, the self-inductance of the coil depends upon the following factors:

(a) Number of turns (N) in the coil (b) Length (l) of the coil
(c) Area of cross-section (A) of the coil (d) Nature of core material

when an inductor is connected in series with a resistor (bulb) with variable frequency source, then current
fl owing in the bulb is
E
I = rms
rms Z
L is the impedance of the A.C. circuit.
where Z R 2 2
2
R is the resistance of the bulb
L is the self inductance of the coil
and ω = 2πf, is the angular frequency of the A.C. source
Bulb (Resistor)

Inductor (Coil)

A.C. ammeter

K Rheostat
A.C. Source
( 0 to 12 V)

Fig. 7.1: To study the factors on which the self-inductance of a coil depends

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