Q 12-04-231JEE MainJEE Main 2018 (16 Apr, Shift 1)Easy
A galvanometer with its coil resistance $25\ \Omega$ requires a current of $1\ \text{mA}$ for its full deflection. In order to construct an ammeter to read up to a current of $2\ \text{A}$ the approximate value of the shunt resistance should be:
Answer: (A) $1.25\times10^{-2}\ \Omega$
The shunt carries $I - I_g$ at the same voltage as the coil:
$$S = \frac{I_gG}{I - I_g} = \frac{10^{-3}\times25}{2 - 0.001} \approx 1.25\times10^{-2}\ \Omega$$
Solution by Sreeraj P, M.Sc Physics