Circuits
Meters placed correctly
Ammeter in series (reads the current), voltmeter in parallel across the resistor (reads the voltage). This is the correct way to measure.
Meters placed correctly — interactive Circuits simulation. Ammeter in series (reads the current), voltmeter in parallel across the resistor (reads the voltage). This is the correct way to measure.
Measuring V and I correctly
Place the ammeter in series for current and the voltmeter in parallel across the resistor for voltage.
This is the standard lab setup. The ammeter carries the loop current; the voltmeter senses the potential difference across the resistor.
- A in series
- V in parallel
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
To correctly measure a resistor's current and voltage, an ammeter must go in series and a voltmeter in parallel. If you set up the meters this way, does the circuit behave exactly as if the meters weren't there?
Predictions to weigh
- No — any meter placement changes the circuit somewhat.
- It depends on the resistor's value.
- Yes — correctly placed ideal meters don't change the circuit's current or voltage at all.
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 meters-correct 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
Correct Meter Placement — V = I·R
An ammeter measures current, so it must be part of the current path — wired in series. A voltmeter measures a voltage difference between two points, so it must be wired in parallel across those points, drawing negligible current of its own.
What the printable worksheet asks students to work out
- For one trial, compute I = E/R1 using E = 9 V. Compare to the table, and confirm the voltmeter reads 9 V in every trial regardless of R1.
- Explain, using the ammeter's 0 Ω and the voltmeter's ∞ Ω, why this placement lets you read the resistor's true current and voltage without perturbing the circuit at all.
Where this shows up beyond the lab
- See the meters-swapped experiment for what happens if the ammeter and voltmeter placements are accidentally reversed. Predict, before looking, whether swapping would make the circuit read zero current, zero voltage, or something else entirely.
- Modern digital multimeters approximate ideal ammeters and voltmeters very closely (extremely low and extremely high internal resistance respectively). Why might an older, less precise meter give a reading noticeably different from the true circuit value?
- 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 Meters Correct
- Select the resistor
- Press Play
- Trust the 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.