Wheatstone Bridge

A Wheatsone Bridge is a useful circuit arrangement that allows accurate measurement of resistance.

A Wheatstone bridge is "balanced" by adjusting resistors R₃ and R₄ so that no current flows through the Galvanometer. Then, the voltage at points A and B in the circuit is the same. Voltage across R₁ is the same as across R₃ and the voltage across R_x is the same as across R₄. Current through R₁ and R_x is the same and current through R₃ and R₄ is the same.

Since points A and B have a common potential we can write

I₁R₁ = I₃R₃

Likewise, we can write

I₁R_x = I₃R₄

Dividing one equation by the other, we have

We can replace the variable resistors R₃ and R₄ with a slidewire with variable length L₃ and L₄,

Kirchoff's Rules			Internal Resistance
Return to Ch 19, DC Circuits

(c) Doug Davis, 2002; all rights reserved