Question

State the principal of Wheatstone bridge?

Answer 1

Explanation:

Let us consider the below circuit where the bridge is in an unbalanced condition and we need to calculate the voltage difference between Q1 and Q2, i.e., Vout and hence the value of R4 needed to make the bridge balanced.

Example of Wheatstone Bridge

As per the voltage division law,

Vq1 = (R3/(R3+R1)) * Vs ,where Vs =100volts (voltage source)

putting values of R3 = 40 ohms, R1=50 ohms ,and Vs= 100 volts, we get

Vq1 = 44.4 volts

Similarly, Vq2 = (R4/(R4+R2)) * Vs

putting the values, R4 =50 ohms, R2 =100 ohms, and Vs =100 volts, we get

Vq2 =33.3 volts

Thus, Vout can be found as,

Vout = Vq1 – Vq2

So, Vout = 44.4 – 33.3 = 11.1 volts

Now to make the bridge balanced, we can find a suitable value for R4 as done below:

R4 = R2 * (R3/R1)

putting the values of R1, R2, and R3, we have

R4 = 100 * (40/50)

= 80 volts

Therefore, R4 = 80 volts is the value of resistor which should be used to make the bridge in a balanced condition.

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