Shown in the circuit is a 20 V battery connected to an arrangement of

Shown in the circuit is a 20 V battery connected to an arrangement of four resistors. If the potential difference between points P and Q in the circuit is zero then :

R = 2 Ω

R = 8 Ω

R = 18 Ω

R = 4 Ω

Answer is Right!

Answer is Wrong!

This question was previously asked in

UPSC Geoscientist – 2024

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The circuit can be analysed as a parallel combination of two series branches. The potential difference between points P and Q is zero when the ratio of resistances in the two branches satisfies the condition for a balanced Wheatstone bridge.

Let the branches be from A to B. Branch 1 has resistors 10Ω and R in series, with P between them. Branch 2 has 5Ω and 10Ω in series, with Q between them. For the potential difference between P and Q to be zero (V_P = V_Q), the potential division must be the same in both branches relative to the terminals A and B. This occurs when the bridge is balanced, i.e., the ratio of resistances in the arms is equal: 10Ω / R = 5Ω / 10Ω.

From the balanced bridge condition, 10 / R = 5 / 10. Cross-multiplying gives 10 * 10 = 5 * R, so 100 = 5R, which means R = 20 Ω. However, 20 Ω is not among the options. This suggests a potential error in the question or provided options. Assuming the intended answer is one of the options provided, and based on external information about this specific question from past exams, option B (R=8 Ω) is indicated as correct in some sources, despite standard calculation leading to R=20 Ω. There is likely an inconsistency in the problem statement as presented or its intended solution.

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