Question

The coil of wire in a galvanometer has a resistance of R_C = 58.7Ω. The galvanometer exhibits a full-scale deflection when the current through it is 0.226 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 12.8 V. What is the resistance of this resistor?

Answer 1

$I=\frac{12.8}{R+R_C}\to IR+IR_C=12.8\to R=\frac{12.8-IR_C}{I}=$

$=\frac{12.8-0.000226\cdot 58.7}{0.000226}=56578\ (\Omega)$ . Answer