To convert galvanometer into ammeter, a very low resistance is connected in parallel with Galvanometer coil. so that Maximum current can flow through it is called shunt.
Uses of Shunt
1. To provide an alternative path for excess current.
2. To convert galvanometer into ammeter.
3. To limit the current in galvanometer.
A sensitive device which is used to detect very small current flowing through in electric circuit is called Galvanometer. it is also termed as moving coil motor. it can be converted as ammeter and voltmeter.
a) Conversion of Galvanometer into Ammeter
A device which is used to measure current flowing through the electric circuit is called a ammeter. if a low resistance is connected in parallel i.e shunt with a galvanometer can be converted into a voltmeter the emitter is Galvanometer with low resistance parallel to it.
Suppose Rs be the value of Shunt resistance and G be the resistance of Galvanometer ,Ig is current flowing through the Galvanometer to produce full scale deflection and I be the total current flowing through the circuit. Since resistance G and Rs are in parallel, the effective resistance R of the circiut is
1/R = 1/G +1/Rs
so, R = GRs/(G+Rs) ……(1)
Also, current through the shunt resistance =I -Ig
Here, p.d across Rs =P.d across G.
(I -Ig)Rs = IgG
Since, Rs = Ig.G/(I – Ig) ……..(2)
This is the required expression of Shunt which when connected in parallel with Galvanometer converts it into ammeter of required range.
Voltmeter is a device which is used to measure potential difference across the end of conductors.
If high resistance wire is connected in series with Galvanometer then it is converted into voltmeter.Thus, Voltameter is a galvanometer with high resistance wire connected in series with it.