Computing the value of a series resistor

Question: Determine series resistance needed to convert a galvanometer to a voltmeter reading 15V on full scale deflection if a current of 2.5 mA causes full scale deflection and the resistance of the coil is 10 ohms?

Answer:

V original meter max = (I full scale deflection) x (R meter) = (2.5 mA) x (10 ohms) = 25 mV
Using the voltage divider principle:
(V original meter max)/(V adjusted meter max)=(R meter)/(R meter + R series)
(25 mV) / (15 V) = (10 ohms) / (10 ohms + R series)
R series =  5990 ohms

Use of a Series Resistor

Question: What device is used to extend the range of a DC voltmeter and how is it connected to the basic meter?


Answer:

A resistor connected in series to the voltmeter can be used to extend the voltmeter's range.