wheatstone bridge An electrical circuit consisting of four resistances connected as shown in fig. w2. The bridge is said to be balanced when there is no current through the galvanometer, G. Application of Kirchhoff,s laws * gives,

R₁ /R₃ =R₂ /R₄

If three resistances R₁, R₂ and R₃ are known, the fourth resistance R₄ can be found. R₁ and R₂ values are fixed, and R₃ is varied to find null deflection in the galvanometer.

A rule of thumb for obtaining reasonably high sensitivity of the bridge, is to have resistances of the four arms approximately equal. The galvanometer must be sensitive to detect the null point accurately.