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Q.
A galvanometer coil has a resistance of $50 \,\Omega$ and the meter shows full scale deflection for a current of $5 \,mA$, This galvanometer is converted into voltmeter of range $0 - 20 \,V$ by connecting
Here,
$R=?$
$G=50 \,\Omega $
$V=20\, V $
$I_{g}=5 \times 10^{-3} A$
where, $G$ : Resistance of the galvanometer
$V$ : Required range of the voltmeter
$I_{g}:$ Current in galvanometer which gives full deflection
$R:$ High resistance in series with galvanometer
Applying the formula
$R =\frac{V}{I_{g}}-G $
$=\left(\frac{20}{5 \times 10^{-3}}\right)-50$
$=4000-50 $
$=3950\, \Omega$
This resistance is connected with galvanometer in series.