Wheatstone Bridge

Linear Circuit Analysis
Chapter 6 .
Engr. Ahmad Bilal

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1 Construction There are two knownresistors, one variableresistor and one unknown resistor connected in bridge form as shown below. By adjusting the variable resistor the current through the Galvanometer is made zero, which helps us to determine unknown resistance

2 Solving Wheat Stone Bridge.

2.1 Points to be observed

1. We have two fixed resistors R1 and R3 2. We have on Variable resistor R2 3. We have one unknown resistor R3.

3 Setting Up the Equipment

1. Set the circuit as shown in figure.

2. Connect a voltmeter or galvanometer between D and B nodes

3. Now start adjusting Variable resistor in such a way that Voltage across or current across galvanometer becomes zero.

4. So the I and V across the measuring device is Zero

4 Redrawing Schematics

 

5 Using VDR

1. The above schematics can be divided in two branches 2. Branch 1 having R1 and R3 in series 3. Branch 2 having R2 and R3 in series 4. As we have mentioned that both sides are equall in in terms of resistance , so let’s do a little operation

Finding v3 (Resistance across R3)

Finding Vx (Resistance across Rx)

Now We know Vs=Vx

=

Cancelling Vs both Side and Cross Multiplying

R3R2 + R3Rx =RxR1 +R3 Rx

Cancelling RxR3 both Side and Cross Multiplying

Rx=R2.R3/R1