Swapped Meters: A Common Wiring Mistake

1 · Predict

If a voltmeter is accidentally wired in series (where the ammeter should go) and an ammeter is wired in parallel (where the voltmeter should go), what happens to the resistor's current, no matter what resistance you choose?

• The current is always zero — the series voltmeter's huge resistance blocks the circuit entirely.
• The circuit still works normally, just with less accurate readings.
• The current becomes dangerously large.

2 · Set Up

1. Open the meters-swapped preset and press Reset. The voltmeter is (incorrectly) in series; the ammeter is (incorrectly) in parallel across the resistor.
2. Enable the current readout on the resistor.
3. Set R1's value for each trial and record the resistor's current.

3 · Collect Data

Plot current I (y-axis) against R1 (x-axis) for your three trials. Is the line flat at zero?

4 · Analyze

1. An ideal voltmeter in series acts as an open circuit (essentially infinite resistance), so no current can flow anywhere in the loop, regardless of R1's value.
2. Explain why the series voltmeter — meant to measure without drawing current — instead blocks all current when it's the only path available, and why the resistor's voltage also reads zero as a result.

5 · Extend

1. The parallel ammeter (0 Ω) actually shorts out the resistor: current preferentially flows through the ammeter instead of R1. In a real circuit with a non-ideal (but still low-resistance) ammeter, this mistake can draw dangerously high current and damage the meter. Explain why 'measure current with an ammeter in parallel' is a real-world wiring hazard, not just a theoretical curiosity.
2. If you built a circuit and found zero current everywhere with a properly-working battery, what would checking your voltmeter's placement tell you about a possible wiring mistake?

The Physics Behind This Experiment

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