Circuits
Metered circuit
Ammeter reads current; voltmeter reads voltage
Metered circuit — interactive Circuits simulation. Ammeter reads current; voltmeter reads voltage Free browser-based virtual physics lab with live SI measurements and a guided tutorial.
Correct meter placement
An ammeter in series measures current; a voltmeter in parallel measures voltage across a component.
Meters are idealized: the ammeter has ~0 Ω resistance and the voltmeter has ~∞ Ω.
- Ammeter in series → I
- Voltmeter in parallel → V
Investigation brief
Plan the question before you open the lab
The brief mirrors the prerendered page: driving question, competing predictions, variable roles, governing laws, setup, analysis and extension prompts remain visible and in this order.
Driving question
An ammeter (in series) and a voltmeter (in parallel) are added to a simple resistor circuit to measure it. Do the meters themselves change the circuit's behavior?
Predictions to weigh
- Yes — adding meters always changes the current and voltage you're trying to measure.
- It depends on which resistor value you're testing.
- No — an ideal ammeter has zero resistance and an ideal voltmeter has infinite resistance, so neither disturbs the circuit.
Variable roles
What you set:
- Resistance R1 (Ω)
What you measure:
- Voltmeter reading V (V)
- Ammeter reading I (A)
How the investigation runs
- Open the metered-resistor preset and press Reset. The ammeter sits in series with R1; the voltmeter sits in parallel across R1.
- Enable both the ammeter and voltmeter readouts.
- Set R1's value for each trial and record the ammeter reading.
Governing equation
Ideal Meter Behavior — V = I·R
An ideal ammeter (0 Ω) placed in series adds no resistance to the loop, and an ideal voltmeter (∞ Ω) placed in parallel draws no current — together they let you read a circuit's true current and voltage without disturbing it.
What the printable worksheet asks students to work out
- For one trial, compute I = E/R1 using E = 9 V. Compare to the table. Notice the voltmeter reading stays 9 V in every trial — explain why.
- An ideal ammeter has 0 Ω, so it drops no voltage — the full battery EMF appears across R1 regardless of R1's value. Explain why this means the voltmeter reading never changes even as R1 (and the current) changes.
Where this shows up beyond the lab
- A real ammeter has a small but nonzero resistance, and a real voltmeter has a large but finite resistance. For very small R1, would a real (non-ideal) ammeter's resistance start to matter more or less compared to R1?
- This experiment places the ammeter in series and the voltmeter in parallel — the only placement that doesn't disturb the circuit. See the meters-swapped experiment for what goes wrong if they're placed the other way around.
- AP Physics 2 — Unit 11: Electric Circuits
- AP Physics C: Electricity and Magnetism — Unit 11: Electric Circuits
- IB Physics — B.5 Current and circuits
- General High School Physics — Electricity & DC circuits
- NGSS High School Physics — Electric current and magnetic fields
- Welcome to Metered Resistor
- Select the resistor
- Press Play
- Two readings
- Open the Properties panel
- You did it!
Open the interactive simulation to build the scene, press Play, and explore with live measurements and a guided tutorial.