Question 1

What is the balance condition of a Wheatstone bridge?

Accepted Answer

For the standard NCERT labeling, the bridge is balanced when P/Q = R/S. At this point the galvanometer carries zero current, so the two points connected through the galvanometer are at the same potential.

Question 2

Why is the galvanometer current zero at balance?

Accepted Answer

The galvanometer joins two nodes that have equal potential at balance. Because their potential difference is zero, no current flows through the galvanometer branch. The source still supplies current through the other arms, so the circuit does not become completely current-free.

Question 3

How is a metre bridge related to a Wheatstone bridge?

Accepted Answer

A metre bridge is a practical Wheatstone bridge in which two arms are sections of a uniform resistance wire. The jockey defines the junction between the two wire sections, while the two gap resistances form the other two arms.

Question 4

What is the balance position on a standard metre bridge?

Accepted Answer

The standard wire is 1 m long, has 100 equal 1 cm divisions, and usually has total resistance 100 Ω. At balance, P/Q = l/(100 - l), where l is the wire length from the left end to the jockey.

Question 5

What happens to the galvanometer current when the jockey crosses the null point?

Accepted Answer

The galvanometer-branch current reverses direction because its two terminals exchange potential. Its magnitude becomes zero at the null point. The current directions in the fixed source-fed arms do not all reverse.

Wheatstone Bridge and Metre Bridge — Find Unknown Resistance by Balance

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Practice