Which of the following statements related to Wheatstone Bridge are correct?
(A) The bridge is most sensitive when all the four resistances are of the same order
(B) The internal resistance of the cell and the resistance of the galvanometer affect the null point
(C) It does not involve measurement of current and potential difference
(D) Resistances of ammeters and voltmeters do not affect the measurements
Choose the correct answer from the options given below:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → (A), (C) and (D) only
The Wheatstone bridge is a null method: at balance no current flows through the galvanometer, and the unknown resistance follows from the balance condition alone.
\( \displaystyle \frac{P}{Q} = \frac{R}{S} \)
(A) The bridge is most sensitive when all the four resistances are of the same order — Correct. A small change in one arm then produces the largest galvanometer deflection, so the balance point is found most precisely.
(B) The internal resistance of the cell and the resistance of the galvanometer affect the null point — Incorrect. The balance condition contains only the four arm resistances; with no current through the galvanometer, neither its resistance nor the cell's internal resistance changes the null point.
(C) It does not involve measurement of current and potential difference — Correct. Only the zero deflection of the galvanometer is observed; no current or voltage is read.
(D) Resistances of ammeters and voltmeters do not affect the measurements — Correct. No ammeter or voltmeter is used, so their resistances cannot introduce an error.