# 27. A galvanometer coil has a resistance of $12 \Omega$  and the metre shows full scale deflection for a current of 3 mA. How will you convert the metre into a voltmeter of range 0 to 18 V?

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

At the full-scale deflection current(I) of 3 mA the voltmeter must measure a Voltage of 18 V.

The resistance of the galvanometer coil G =  $12 \Omega$

$I$$\times$$(R+G)=18 V$

$R=\frac{18}{3\times 10^{-3}}-12$

$R=6000-12$

$\\=5988\Omega$

The galvanometer can be converted into a voltmeter by connecting a resistor of resistance $5988\Omega$ in series with it.

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