In metre bridge experiment, the null point is obtained at 20 ~cm from left end of the wire, when resistance X is balanced against another resistance Y(X

Options

1. A40 ~cm
2. B80 ~cm
3. C60 ~cm
4. D50 ~cm

Correct answer

D. 50 ~cm

Step-by-step solution

The correct option is (D). Concept: Meter bridge experiment is based on two facts: (1) the resistance across a wire is directly proportional to its length (2) balanced Wheatstone bridge has null deflection when the ratio of resistances is equal, and no current flows through the circuit. The current through galvanometre is zero, when the ratio of resistances, i.e., P Q = R S . As given in the problem, P=X, Q=Y, R 20 ~cm and S 80 ~cm . Therefore, X Y = 20 80 = 1 4 Similarly, to balance a resistance P=4 X against Q=Y

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