Sample 1Medium
In a Wheatstone bridge, P = 10 Ω is between A and B, Q = 20 Ω between B and C, R = 15 Ω between A and D, and S = 30 Ω between D and C. A galvanometer connects B and D. What is the equivalent resistance between A and C?
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The answer is A.
P/Q = R/S = 1/2, so the bridge is balanced and no current flows through the galvanometer. The branches ABC (30 Ω) and ADC (45 Ω) are then in parallel: 30 × 45 / 75 = 18 Ω.
- B.
75 Ω adds all four resistors in series.
- C.
12 Ω does not come from the two arms in parallel.
- D.
30 Ω is only the ABC arm.
NCERT: Class 12 Physics, Chapter 3