Question

An ammeter is to be constructed which can read currents up to 2.0 A. If the coil has a resistance of 25 $\Omega$ and takes 1 mA for full-scale deflection, what should be the resistance of the shunt used ?

Answer 1

$g=25Wig=1mA$

$i_g=2AS=?$

$\text{Potential across AB is same}$

$25\times {10}^{-3}=(2-{10}^{-3})S$

S = $\frac{25\times {10}^{-3}}{2-{10}^{-3}}=\frac{25\times {10}^{-3}}{1.999}$

$=12.5\times {10}^{-3}=1.25\times {10}^{-2}$