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# A galvanometer coil has a resistance of 15 ohm ​​​​​​​ and the metre shows full scale deflection for a current of 4 mA. How will you convert the metre into an ammeter of range 0 to 6 A?

28. A galvanometer coil has a resistance of $15 \Omega$  and the metre shows full scale deflection for a current of 4 mA. How will you convert the metre into an ammeter of range 0 to 6 A?

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The galvanometer can be converted into an ammeter by connecting an appropriate resistor of resistance R in series with it.

At the full-scale deflection current(I) of 4 mA, the ammeter must measure a current of 6 A.

The resistance of the galvanometer coil is G =  $15 \Omega$

Since the resistor and galvanometer coil are connected in parallel the potential difference is the same across them.

$IG=(6-I)R$

$\\R=\frac{IG}{6-I}\\ \\R=\frac{4\times 10^{-3}\times 15}{6-4\times 10^{-3}}\\ R\approx 0.01\Omega$

The galvanometer can be converted into an ammeter by connecting a resistor of resistance $0.01\Omega$ in parallel with it.

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