Conversion of galvanometer into ammeter

What is Galvanometer :

Galvanometer is a electrical device with high sensitivity, it's use for detection of small amount of current due to resion of its high sensitivity. Galvanometer works on principal of torque acting on current carrying coil in a magnetic field.

What is Ammeter :

It is a electronic device which used for detection of high amount of current. Ammeter can be detect AC and DC both current. It's always connect in series combination in circuit.

HOW TO CONVERT GALVANOMETER INTO AMMETER :

We can convert a Galvanometer into ammeter easily by using following circuit combination.

When we connect a low resistance in parallel with the galvanometer then it's works as ammeter. And this low resistance is called shunt resistance , the range of ammeter depends on the shunt resistance and the scale will be in ampere.

        Let's assume I current passing through the Circuit, and this I current devided in two part at junction A , one part is Ig and another current is I-Ig , Here Ig is current passing through galvanometer and I-Ig is current passing through shunt resistance. In this combination between galvanometer and shunt resistance the potential will be same because in parallel combination the potential always same. Now we calculate current passing through galvanometer- 

Vgalvanometer = Vshunt

According to ohm's law V = IR 

IgRg = (I-Ig)S

IgRg-IS-IgS = 0

Ig(S+Rg)-IS = 0

Ig(S+Rg) = IS 

Then 

Ig = SI/(S+Rg)    -----(1)

From equation (1)

Ig∝ I 

In Galvanometer the deflection is directly proportional to current passing through it , so 

θ∝Ig or θ∝I 

θ = Ig/G 

So , the deflection in Galvanometer is measure the current I passing through the Circuit .