Answer to Question #214209 in Electric Circuits for Kamran

Question

A G coil with its internal resistance 15 Ω, shows its full-scale deflection at 2 mA. How would you 

convert it into an A of range 0-5 A and a V of range 0-15 V? Give detailed calculations and draw 

the circuit diagrams for these conversions by mentioning the evaluated values of resistances.

Answer 1

Resistance on galvanometer, $G=15\Omega$

current passing through the galvanometer, $I_g=2mA=2\times 10^{-3}A$

current across the ammeter, $I=5A$

use the formula, $S=\frac{I_g.G}{I-I_g}=\frac{2\times 10^{-3}\times 15}{5-0.002}=6m\Omega$

A short resistance of $6m\Omega$ has to be connected in parallel to the galvanometer to convert it to an ammeter.