Chapter-3|Current Electricity| NCERT 12th Physics:
It is a electrical instrument. It measured the value of unknown resistance. It works on the principle of wheatstone bridge.
Wire of length 1 m=100 cm and uniform cross section area A. Wire must be so that it is temperature independence (does not increase resistance after increasing temperature).
We will find out null point D by moving Jockey, until Galvanometer does not show any movement.
Point D -: Where G shows no deflection.
→No current in branch CD.
Now, It work like balanced wheatstone Bridge.