Step 1: Principle of Wheatstone's Bridge.
Wheatstone's bridge is used to measure an unknown resistance by balancing two legs of a bridge circuit. The principle of the Wheatstone bridge is that when the bridge is balanced, the ratio of resistances in one leg is equal to the ratio of resistances in the other leg. Mathematically, this is given by:
\[
\frac{R_1}{R_2} = \frac{R_3}{R_4}
\]
where \( R_1, R_2, R_3, \) and \( R_4 \) are the resistances in the four arms of the bridge.
Step 2: Analyzing the given circuit.
In the given circuit diagram, the resistances are: \( R_1 = R_2 = 20 \, \Omega \), \( R_3 = R_4 = 20 \, \Omega \), and the ammeter is placed in one of the branches of the bridge. Given that the Wheatstone bridge is balanced, the current measured by the ammeter will be zero when the bridge is balanced, meaning there will be no current flowing through the ammeter in the ideal balanced condition.
Step 3: Conclusion.
In the balanced Wheatstone bridge, the current measured by the ammeter is zero. However, if the bridge is unbalanced, the current can be calculated using the formula:
\[
I = \frac{V}{R_{\text{total}}}
\]
where \( V = 60 \, \text{V} \) and \( R_{\text{total}} \) is the total resistance of the circuit.
