Voltmeter

A voltmeter is an instrument which is used to measure the potential difference between two points. Always remember the following:

• A voltmeter is always placed in parallel with the resistor(s) when measuring the potential difference
• A voltmeter always has a high impedance (resistance) so that it draws a negligible current, and so does not disturb the circuit.

Instructions:

You are given three resistors which are connected in series, and the combination connected across the terminals of a battery which maintans an overall voltage V. You are also given a voltmeter to measure the voltage at the junctions of each of the resistors (shown as red dots). One terminal of the voltmeter is connected to ground (the green dot). The other probe is floating, and you can connect it to any point in the circuit to measure the voltage at that point. (Hold down the left mouse button to drag the probe. As you make a measurement the voltmeter display turns red.)

Measure and note all of the voltages, then fill in the answers to the questions below. When you have finished, you can check your answers, with the responses appearing in the boxes to the right.

Remember: the voltage which you measure is always the potential at that point relative to gound. The voltage across a resistor is defined as a potential difference between in two ends.

Resistors in Series

You also know that for resistors in series, the current through each resistor is the same. Now that you know all the voltages, and all of the resistances, use Ohm's Law to calculate the currents separately, to verify that they are indeed all the same.