2dix-The Student Choice
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To measure the inductance of a given coil by Anderson Bridge method.

 

OBJECT: To measure the inductance of a given coil by Anderson Bridge method.

APPARATUS REQUIRED: 

Anderson Bridge circuit, Potentiometer, inductors, capacitors, power supply, connecting wires.

THEORY:

Anderson’s Bridge enables the measurement of inductance in terms of a capacitors and resistance. In experimental arrangement P,Q and R are non inductive resistance arms of the bridge. A non inductive resistance S in series with the given coil of unknown inductance ‘L’ is put in the fourth arm of the bridge between F&D.A variable resistance r and a variable condenser c are put in the parallel to the resistance P .An audio amplifier with speaker is put in between the point ‘E’ and ‘D’ and an audio frequency oscillator with a value control is put between the terminal of ‘A’ and ‘C’. The condition of balance in this case is that the potential at ‘D’ and ‘E’ are same. Under this condition no current flows through path DE and the current in various branches. At balance condition, Using Kirchhoff’s laws we have (in loop ABCD)

I1P+(I1+I2)Q=I3(R+S+L)

In loop BCD

I1P-I2(r+1/C) =0

In loop DCO

I2/C =I3R

Where f is the frequency of the A.C .shown by oscillator

C=Capacity of a condenser

S=Total resistance of the CD

It includes the resistance of the inductance coil and variable resistance S.

By substituting, we have

I1(P+Q)=I2[(R+S+L)/CR-Q]

And by eliminating

S=RQ/P

Which is the relation satisfied by the bridge for steady currents and by equating real parts, we have

L=[CR(Pr+Qr+PQ)]/P

And if P=Q, we have

L=CR(Q+2r)

 

CIRCUIT DIAGRAM:

Fig: 10.1 Anderson Bridge method.

 

PROCEDURE:

1. The connection is made as shown in. Now keep the ratio arms (P:Q)1:1 and resistance in the R branch should be of the order of the resistance in the CD branch.

2. Now adjust the condenser to some value ‘C’. Now adjust r in the way that the sound in the speaker is reduced to minimum.

3. Note down the value of P, Q, R, r and C.

4. Constant Repeat the experiment by changing, keeping P,Q and R. Note down the value of r and C.

 

 

 

 

 

 

 

OBSERVATION TABLE:

  Frequency of the A.C. source=1 KHz

S. No.

  P(Ω)

  Q(Ω)

    R(Ω)

   r(Ω)

  C(µf)

  L=CR(Q+2R)

    Henries

  1.

 

 

 

 

 

 

  2.

 

 

 

 

 

 

  3.

 

 

 

 

 

 

  4.

 

 

 

 

 

 

  5.

 

 

 

 

 

 

 

RESULT:

             Inductance of the given coil=                  Henries.

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