Measurement of unknown capacitance using De Sauty Bridge.

Experiment No.: 09

Aim of the Experiment: –

Measurement of unknown loss-free capacitor using De-Sauty’s bridge.

Apparatus Required: –

Sl. No.NameSpecificationQuantity
1De-sauty’s bridge kit1
2Head Phone1
3Connecting WiresAs per required
Table No. 9.1

Circuit Diagram: –

fig. 9.1

Theory: –

This bridge is used to determine unknown capacitance by comparing it with known standard capacitor.

Arm of the bridge are as follows: –

  1. The first arm ab contains a loss free unknown capacitor C1µF.
  2. The second arm ad contains a known capacitance in the form of single decade of 10* 0.01µF.
  3. The third arm bc contains a non-inductive variable resistance R3 in the form of three decades of 10*10Ω, 100*100Ω, and 10*1000Ω.
  4. The fourth arm cd also contains a non-inductive variable resistance R4 in the form of three decades of 10*10Ω, 100*100Ω, and 10*1000Ω.
  5. An oscillator of 1kHz is used as supply.
  6. 4mm sockets are provided to connect head phone.

The four arm Impedance of the bridge are,

\[\color\red{Z_1 = \dfrac{-j}{wC_1}}\] \[\color\red{Z_2 = \dfrac{-j}{wC_2}}\] \[\color\red{Z_3 = R_3}\] \[\color\red{Z_4 = R_4}\] \[\color\green{Under\; balanced \;condition \;of\; the\; bridge,}\] \[\color\red{Z_1Z_4 = Z_2Z_3}\] \[\color\red{C_1 = \dfrac{R_4}{R_3}\times{C_2}}\]

Procedures: –

  1. Keep C2 at a certain value.
  2. Now adjust the decade resistance dial R3 and R4 so asto minimize the second in the headphone.
  3. Note the value of resistance dial R3 , R4 and C2 and calculate the value of unknown capacitor C1 using above formula.
  4. Repeat the above procedures for all other values of the capacitor C1 .

Observation Table: –

Sl. NoC2 in faradR3 in Ohms.R4 in Ohms.C1 in farad
1
2
3
4
5
6
7
8
Table No. 9.2

Calculation:

\[\color\red{C_1 = \dfrac{R_4}{R_3}\times{C_2}}\]

Conclusion: –

To be written by Student.

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