Chapter-4|Moving Charges and Magnetism| NCERT 12th Physics:
Conversion of Galvanometer Into an Ammeter:
Ammeter: A device used to measure electric current.
Ammeter is always connected in series with appliance.
A galvanometer can be converted into an ammeter by connecting a very low resistance called (shunt S) in parallel with galvanometer.
Since, Potential difference across Galvanometer and shunt will be equal because they are connected in parallel.