A galvanometer of resistance `16 Omega `shows a full scale deflection for a curent of 20 mA. The only shunt resistance that is available is `0.06 Omega` but it is not sufficient into an ammeter having a range of 8A. How much resistance should be connected in series with the galavanometer to get the ammeter of the desired range?

Explanation

Data: `G=16Omega, I_(g) =20 mA=0.02 A`,
`S=0.04 Omega, I=10 A`
Let X be the resistance to be connected in series with the coil of the galvanometer.
The fraction of the current through the galvanometer is `I_(g)/I`.

`I_(g)/I= S/((G+X) +S)`
`therefore (G+X) + S = I/I_(g) xx S = 10/0.02 xx 0.04 =20`
`therefore X=20-(16+0.04) = 3.96 Omega`