Current Electricity Ques 11
11. 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 $S$ ?
(a) $3 \Omega$
(b) $6 \Omega$
(c) $1 \Omega$
(d) $2 \Omega$
[2007]
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Answer:
Correct Answer: 11.(a)
Solution:
- (a) A balanced wheatstone bridge simply requires
$\frac{P}{Q}=\frac{R}{S} \Rightarrow \frac{2}{2}=\frac{2}{S}$
Therefore, $S$ should be $2 \Omega$.
A resistance of $6 \Omega$ is connected in parallel.
In parallel combination, the voltage across each component is the same.
$\frac{1}{R_{\text{eq}}}=\frac{1}{R_1}+\frac{1}{R_2}$
$\frac{1}{2}=\frac{1}{6}+\frac{1}{S} \Rightarrow S=3 \Omega$
If the resistance is connected in parallel to the right gap resistor in the metre bridge, then balancing length decreases and hence jockey moves towards left.
BETA
