Conversion of Galvanometer into Ammeter:
Galvanometer is a very delicate and sensitive electrical instrument used to detect current in an electrical circuit whereas an ammeter is an electrical instrument specifically used to measure current in an electrical circuit.
As the resistance of the galvanometer is generally low, a small current can deflect its coil to the fullest extent. Therefore, if a large current is passed through a galvanometer, it may get damaged. To protect the galvanometer, a suitable low-resistance S is connected in parallel, called a shunt.
Conversion of Galvanometer into Voltmeter:
Voltmeter is an electrical instrument used to measure the potential difference between any two points of a part of an electrical circuit by connecting it in parallel. A galvanometer can be converted into a voltmeter by connecting a very high resistance in a series called a multiplier.