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Wheatstone bridge
Intermediate
Balanced when ratios of resistances are equal.
P/Q = R/SFour resistors in a diamond with a galvanometer across the middle. When P/Q = R/S no current flows through it, which lets you find an unknown resistance precisely.
P = 100, Q = 200, R = 150: S = 300 Ω.
Works because of equal potentials, regardless of the supply voltage.
In more detail
A Wheatstone bridge has four resistors arranged in a diamond with a galvanometer across the middle. When the bridge is balanced, no current flows through the galvanometer, which lets unknown resistances be measured precisely.
Real-world uses
- Strain gauges and sensors are read using Wheatstone bridges.
- Precision laboratories use bridges to measure resistances accurately.
- Engineers use a Wheatstone bridge to measure an unknown resistance precisely, by balancing it against known ones.
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Frequently asked questions
What is the balance condition?
R1/R2 equals R3/R4, so the galvanometer reads zero.
Why is it precise?
Because the measurement depends on ratios, not on the absolute voltage.
How do I know the bridge is balanced?
The galvanometer shows zero current, which means the potentials at the two midpoints are equal.
Related topics in Current Electricity & Circuits
Cells in series and parallel · Kirchhoff's current law · Kirchhoff's voltage law · Meter bridge · Potentiometer · Ammeter and voltmeter