Page 49 - Physics - XII

Principle/Theory
V
1. Resistance of an inductor: The resistance of inductor coil without core is given as R = where V is
I
the potential diff erence across the coil and I is the D.C. current fl owing through the coil. If we introduce

a soft iron core, let the new values of potential diff erence across the coil is V' and D.C. current is I'
V'
fl owing through it. Hence, resistance R' of inductor coil with soft iron core is given as R' = .
I'
V
2. Impedance of an inductor: The impedance Z of an inductor coil without iron core is given by Z = ac.. ,
I ac..
where V and I are the A.C. voltage across the coil and A.C. current fl owing through the coil without
a.c. a.c.
iron core.
V'
If a soft iron is introduced inside the coil, then its impedance Z' can be given as Z' = ac.. where V'
' I ac .. a.c.

is the A.C. potential drop across the coil and I' is the A.C. current fl owing through the coil with soft
a.c.
iron core.

Procedure

1. Determinati on of Resistance of an Inductor

(a) Without soft iron core:

1. Arrange the circuit elements and apparatus as per the circuit diagram as shown in Fig. 1.1(a)
and make all the connections neat, clear, and tight, keeping the key K open. Connect D.C.
battery eliminator, D.C. milliammeter, and inductor in series and D.C. voltmeter in parallel
with the inductor.
2. Adjust the battery eliminator to the lowest setting and switch on the eliminator. Now, insert
the plug key K. Adjust the resistance R with the help of resistance box, so that the readings
are within scale of milliammeter and voltmeter and measure D.C. current through the inductor
(I) and D.C. voltage across the inductor (V) with the help of D.C. milliammeter and D.C.
voltmeter.
3. Set the eliminator to higher voltages in regular steps and note the D.C. current through the
inductor and D.C. potential diff erence across the inductor.
(b) With soft iron core:

4. Introduce the given soft iron core in such a way so that the core is fully inside the inductor coil.
5. Repeat the steps 2 and 3 and note the observations.

Observations

Range of D.C. voltmeter = 0 to _____ V
Least count of D.C. voltmeter = _____ V

Range of D.C. milliammeter = 0 to _____ mA
Least count of D.C. milliammeter = _____ mA

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