# Lab Experiment for Schering Bridge

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###### AIM

Find the value of unknown capacitance using a Schering bridge.

###### REQUIREMENT

• Trainer Kit.
• Multimeter.
• CRO.
• Patch chords.

###### PROCEDURE - I

• Connections are made as per the connection diagram shown above.
• Connect the unknown capacitance at the Cx (unknown) point.
• Keep R4, R3 in minimum position.
• Connect the CRO across P and Q.
• Switch ON the unit.
• Vary resistance R3 to some extent. (Above 2K is suggested).
• Choose C2, such that you can obtain a maximum variation of output.
• Vary the potentiometer R4 such that the amplitude of sine wave will decrease and at one point it will obtain a minimum of zero amplitude and then it will start increasing at that point stop the tuning and vary R3. Here also the amplitude of sine wave will decrease and at one point it will obtain a minimum of zero amplitude and then it will start increasing at that point stop the tuning.
• Repeat the above step such that you will obtain minimum amplitude or zero amplitude.
• Remove the patching at R4 and R3, find the resistance using multimeter and note down the reading according to the table given below and calculate the value of unknown capacitance.
• One can verify the balancing condition by connecting the bridge output (P & Q) to the input(P & Q) of audio power amplifier and you can hear a minimum voltage or no voltage. If you vary the potentiometer R4 you can hear a maximum voltage.

###### PROCEDURE - II

• Connections are made as per the connection diagram shown above.
• Connect the unknown capacitance at the Cx (unknown) point.
• Keep R4, R3 in minimum position.
• Connect the multimeter across P and Q (AC mode).
• Switch ON the unit.
• Vary resistance R3 to some extent. (Above 2K is suggested).
• Choose C2, such that you can obtain a maximum variation of output.
• Vary the potentiometer R4 such that the output voltage will decrease and at one point it Will obtain a minimum voltage or zero voltage and then it will start increasing at that point stop the tuning and vary R3. Here also the voltage will decrease and at one point it will obtain a minimum voltage or zero voltage and then it will start increasing at that point stop the tuning.
• Repeat the above step such that you will obtain minimum voltage or zero voltage.
• Remove the patching at R4 and R3, find the resistance using multimeter and note down the reading according to the table given below and calculate the value of unknown capacitance.
• One can verify the balancing condition by connecting the bridge output (P & Q) to the input (P & Q) of audio power amplifier and you can hear a minimum voltage or no voltage. If you vary the potentiometer R4 you can hear a maximum voltage.

###### TABULATION

 SL; NO C2   (; F) R3 ohms R4 ohms CX Theoretical CX   Practical

###### RESULT

Thus the value of unknown capacitance was measured using a Schering Bridge.