Worksheet: Using Voltmeters
In this worksheet, we will practice connecting voltmeters in circuits to measure potential drops across components, calibrated so as to give reliable readings.
Analog meters use a galvanometer, which essentially consists of a coil of wire with a small resistance and a pointer with a scale attached. When there is a current in the coil, the pointer turns; the amount the pointer turns is proportional to the amount of current in the coil. Galvanometers can be used to make a voltmeter if a resistor is placed in series with the galvanometer. Consider a galvanometer that has a resistance of 25.00 Ω and gives a full scale reading for a 50.00-μA current. The galvanometer is to be used to make a voltmeter that has a full scale reading of 10.00 V, as shown. Recall that a voltmeter is connected in parallel with the component of interest, so the meter must have a high resistance or it will change the magnitude of current in the component.
What is the potential drop across the series resistor in the meter?
What is the resistance of the parallel resistor?