Question

The resistance of a moving coil galvanometer is 5 $\Omega$. The maximum current it can measure is 0.015A. To convert it into an ammeter to measure 1.5 A :

• A. connect 5/99 $\Omega$ in series
• B. connect 99/5 $\Omega$ in parallel
• C. connect 5/99 $\Omega$ in parallel
• D. connect 99/50 $\Omega$ in series

Answer 1

The correct option is C connect 5/99 $\Omega$ in parallel

To measure current of $15A$, we have to chose $R$ and connect it in parallel to make galvanometer an ammeter such that $I_g$ remains $0.015A$

$I=1.5A$ and $R_g=5\Omega$

Now, current through galvanometer that is through resistance $R_g$is given by $I_g=\frac{R}{R+R_g}I$

$⟹0.015=\frac{R}{R+5}\times 1.5$

$⟹R+5=100R$

$⟹R=\frac{5}{99}\Omega$

Answer_(C)