Definition: A resistor having a very low value of resistance such type of resistor is called shunt resistance. The shunt resistor is mainly made of the material having the low-temperature coefficient of resistance. It is connected in parallel with the ammeter whose range is to be extended. It is also connected in series with the load whose current is to be measured.
Consider an ammeter having its own resistance Rm and it measured only a small current Im. A shunt resistor Rs is placed in parallel with the ammeter for extending their range.
Let, Rs = Shunt resistance
Is = Shunt current
I = total load or circuit current to be measured
From above equation we get,
Where N is the ratio of the total current (I) to be measured to the full-scale deflection current Im is known as the multiplying power of the shunt.
The shunt is also used with a galvanometer to measure current. The galvanometer is an instrument which is used to detect the presence of current and its direction of flow in any branch of the circuit. The galvanometer is designed to carry a very small current. When they are used to measure current parallel shunt are connected in parallel with them