Measuring Devices ( Galvanometer, Voltmeter and Ammeter & Meter Bridge ): Practice Problem & Solution
Three resistances P, Q, R each of $2\Omega$ and an unknown resistance S form the four arms of a Wheatstone bridge circuit. When a resistance of $6\Omega$ is connected in parallel to S the bridge gets balanced. What is the value of S? (2007)
Solution Explained:
To solve this problem, we apply the core principles of Measuring Devices ( Galvanometer, Voltmeter and Ammeter & Meter Bridge ). Understanding the underlying formula is key to arriving at the correct answer below:
For the Wheatstone bridge to be balanced with $P=Q=R=2\Omega$, the equivalent resistance of the fourth arm must also be $2\Omega$.nThe fourth arm is $S$ in parallel with $6\Omega$, so $\frac{6S}{S + 6} = 2$.n$6S = 2S + 12 \implies 4S = 12 \implies S = 3\Omega$.
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