Page 138 - Physics - XII

Procedure

1. Assemble the circuit as shown in Fig. 7.1.
2. Switch on the A.C. supply, insert the plug into the key, and adjust the constant current in the circuit by
using rheostat. The frequency of the source is 60 Hz and voltage is 6 V.
3. Note the current in A.C. ammeter and observe the brightness of the bulb.
4. Put a soft iron rod inside the inductor core and record the current in A.C. ammeter and again observe
the brightness of the bulb. It is observed that the current in A.C. ammeter and brightness of the bulb,
both decreases.
5. Now, switch off the A.C. supply and decrease the frequency of A.C. source, say 50 Hz.

6. Again switch on the A.C. supply and adjust the current in the circuit at the same constant voltage 6 V
by using the rheostat. Observe the current in A.C. ammeter and brightness of the bulb. The current and
brightness both increases.
7. Again, insert the soft iron rod in the core of the coil and observe the A.C. current and brightness of the
bulb. The current and brightness both decreases.

8. Repeat the steps 5, 6, and 7 for diff erent frequency of A.C. source (40 Hz, 30 Hz, and 20 Hz).

Observations
Least count of ammeter = _____ A

Zero error of ammeter = _____ A
Range of ammeter = 0 to _____ A
To study the factors aff ecting self-inductance of a coil

S. Frequency of Current in ammeter Current in ammeter
No. applied voltage (without iron rod in the coil) (with iron rod in coil)
(Hz) (A) (A)

1. 60
2. 50

3. 40

4. 30

5. 20

Result
1. It is observed that the current in the circuit decreases on inserting the iron rod in the core of the coil at
constant frequency of applied voltage and brightness of the bulb decreases and vice-versa.
2. The current in the circuit increases on decreasing the frequency of applied voltage and the brightness

of the bulb increases and vice-versa.

Precautions
1. The current should be passed for a short time to avoid the heating eff ect.

2. The coil should have large number of turns.

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