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PRACTICE · MEMBERSIntermediate · Single correct

PRACTICE / Post office box experiment

Read the four bridge arms

Between nodes A and C, one branch is A–P–B–Q–C and the other is A–R–D–X–C. A detector between B and D reads zero. P = 100 Ω, Q = 1000 Ω and R = 47 Ω.

ACBDP: 100 ΩR: 47 ΩQ: 1000 ΩX: ?GNull detector
The supply connects across A–C. The detector reads zero between B and D.

Find the unknown resistance X.

Organize the givens & assumptions
  • P = 100 Ω
  • Q = 1000 Ω
  • R = 47 Ω
  • Detector current B–D is zero

Ideal bridge and source connected across A and C; negligible lead resistance and true detector null.

  1. A4.7 Ω4.7\ \Omega
  2. B47 Ω47\ \Omega
  3. C1047 Ω1047\ \Omega
  4. D470 Ω470\ \Omega

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