A multi range voltmeter can be constructed by using a galvanometer circuit as shown in Fig. 4.2. We want to construct a voltmeter that can measure 2V, 20V and 200V using a galvanometer of resistance 10 and that produces maximum deflection for current of 1 mA. Find R₁, R₂ and R₃ that have to be used.

Question

Philoid · Accepted Answer

As the galvanometer limit is 1mA we need to find the voltage drop across it’s to measure the voltage. For that we will replace the galvanometer with a resistance equal to its internal resistance.

The maximum voltage drop across the 10Ω resistance will be,

V = 10 × 10^-3 v

=10^-2 v

So, D point should not exceed 10^-2v.

Using kcl in the branch AD

= 2 kΩ

Now, from BD we get

=18 kΩ

From CD we get

=180 kΩ