Wheatstone’ bridge is a device used to determine unknown resistance. It consists of 4 arms of resistances P, Q, R & , a galvanometer of resistance ‘G’ & a battery with plug key. Let ‘I’ be the main current & splits into branch current I1 & I2 respectively.
Applying KVL to the mesh ABDA
I1P + IgG – I2R = 0 ………..(1)
parallelly to the mesh BCDB
(I1 – Ig)Q – (I2+ Ig)* – IgG = O ….(2)
The wheatstone bridge is said to be balanced when no current flowing through the galvanometer.
i.e., Ig = 0
eqn (1) I1P – I2R = 0
I1P – I2R …………(3)
eqn (2) is I1Q – I1S = 0
I1Q – I2S ………….. (4)
This is the balanced condition of Wheatstone bridge.
