Question

In a bridge circuit for measuring resistance, the galvanometer and the key were connected by mistake as shown in Fig.. How can the bridge be adjusted to equilibrium if one observes the galvanometer reading during the opening and closing of the key?

 

Answer 1

Answer: If the bridge is balanced, the galvanometer reading will be the same with the key open or closed.

Explanation:

Unbalanced bridge: The potentials of points A and B are different. When the key is closed, current flows through the lead AB, and, therefore, the distribution of all the currents in the circuit changes. This is equivalent to a change in the entire resistance of the circuit and results in a change in the current flowing through the battery. In an unbalanced circuit, the galvanometer reading will change when the key is opened or closed.

Balanced bridge: The potentials of points A and B are the same. The current distribution in the circuit and the current flowing through the battery do not change, regardless of the position of the key.