In a Wheatstone bridge, there are four resistances \( R_1, R_2, R_3, R_4 \), and a galvanometer \( G \) is connected between the junctions of \( R_1 \) & \( R_2 \) and \( R_3 \) & \( R_4 \). The bridge is said to be balanced when the galvanometer shows zero current, i.e., there is no potential difference across it.
The relation for balance condition is:
\[
\frac{R_1}{R_2} = \frac{R_3}{R_4}.
\]
In this condition, the ratios of the resistances in the two halves of the bridge are equal.