A galvanometer having a coil resistance of $60 \Omega$ shows full scale deflection when a current of 1.0 A…
A galvanometer having a coil resistance of $60 \Omega$ shows full scale deflection when a current of 1.0 A passes through it. It can be converted into an ammeter to read currents upto $5.0 \mathrm{~A}$ by
putting in parallel a resistance of $240 \Omega$
putting in series a resistance of $15 \Omega$
putting in series a resistance of $240 \Omega$
putting in parallel a resistance of $15 \Omega$
Solution
Key Idea To convert a galvanometer to ammeter a small resistance is connected in parallel to the coil of the galvanometer.
$\begin{aligned}
& \text {Here, } \mathrm{G}_1=60 \Omega, \mathrm{I}_{\mathrm{g}}=1.0 \mathrm{~A}, \mathrm{I}=5 \mathrm{~A} \\
& \mathrm{I}_{\mathrm{g}} \mathrm{G}_1=\left(\mathrm{I}-\mathrm{I}_{\mathrm{g}}\right) \mathrm{S} \\
& \mathrm{S}=\frac{\mathrm{I}_{\mathrm{g}} \mathrm{G}_1}{\mathrm{I}-\mathrm{I}_{\mathrm{g}}}=\frac{1}{5-1} \times 60=15 \Omega
\end{aligned}$
Putting $15 \Omega$ resistance in parallel.