Question

The coil of wire in a galvanometer has a resistance of RC = 78.0 Ù. The galvanometer exhibits a full-scale deflection when the current through it is 0.440 mA. A resistor is connected in series with this combination so as to produce a voltmeter. The voltmeter is to have a full-scale deflection when it measures a potential difference of 21.0 V. What is the resistance of this resistor?
Vc = I*Rc = 0.44*10^-3 * 78=0.0343 Volts

R = Vr/I = (21-0.0343)/0.44*10^-3 = 47,649 Ohms.
R+78 = 21/0.44*10^-3 = 47,727.3,
R = 47,649.3 Ohms.

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