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  • A multirange voltmeter can be constructed by using a galvanometer circuit as shown in figure. We want to construct a voltmeter that can measure 2 V, 20 V and 200 V using a galvanometer of resistance 10 Ω and that produces maximum deflection for a current

A multirange voltmeter can be constructed by using a galvanometer circuit as shown in figure. We want to construct a voltmeter that can measure 2 V, 20 V and 200 V using a galvanometer of resistance 10\Omega and that produces maximum deflection for a current of 1 mA. Find R_1, R_2 and R_3 that have to be used,

Answers (1)

The device named galvanometer can also be used to measure the voltage across a given circuit section just like a voltmeter. To do so, a very high resistance wire is connected to the galvanometer in series. The relation is determined by Ig (G + R) – V in which Ig is galvanometer’s range, G is its resistance and R represents the resistance of the wire connected to the galvanometer in series.

Applying the expression in a different situation

For i_{G}(G+R_{1})=2 for 2V range

For i_{G}(G+R_{1}+R_{2})=20 for 20V range

And for i_{G}(G+R_{1}+R_{2}+R_{3})=200 for 200V range

By solving we get

R_{1}=1990 \Omega , R_{2}=18k\Omega and R_{3}=180 k \Omega

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