Ideal meters: ammeter 0 Ω, voltmeter ∞ Ω

The mistake

Placing meters without accounting for their ideal resistance.

Why it feels right

Meters seem like passive observers that don't change the circuit.

How to catch it

You connected a voltmeter in series or an ammeter in parallel.

The first principle

An ideal ammeter (0 Ω) goes in series so all current passes through it; an ideal voltmeter (∞ Ω) goes in parallel so it draws no current.

worked mini-example

How do you measure the current through a resistor?

Common wrong move

Put the ammeter in parallel with it.

Correct

Put the ammeter in series so the same current flows through both.

Test the repair CIR-02 · transfer

To measure the potential difference across a lamp without substantially changing the circuit, connect an ideal voltmeter:

In series with the lamp In parallel with the lamp Across the battery only In place of the lamp

Make a fresh prediction before referring to the worked example.