Wheatstone Bridge Balance

A Wheatstone bridge is balanced when the two middle nodes are at the same electric potential, so no current flows through the detector branch. In that case, the ratio of the resistors in one side of the bridge must match the ratio on the other side, which gives R1/R2 = R3/R4. This comes directly from applying Kirchhoff’s laws to the two branches and demanding zero galvanometer current.

Use this relation when analyzing or designing bridge circuits for precise resistance comparison, sensor readout, or calibration. It is especially useful when you need to determine an unknown resistor or tune a circuit so that a null detector reads zero.

• Swapping resistors from opposite arms and setting the wrong ratios equal
• Forgetting that the formula applies only at balance, when the detector current is zero
• Using the relation with an unbalanced bridge without checking whether the null condition is satisfied