Ammeter and Voltmeter
Simple Explanation
An ammeter measures current and must be connected IN SERIES in a circuit (so all the current to be measured flows through it). A voltmeter measures potential difference and must be connected IN PARALLEL across the component being measured.
Why Do We Need It?
Connecting these instruments correctly is essential — connecting them the wrong way can give inaccurate readings or even damage the instrument or circuit.
Why Does This Work?
An ammeter is designed with very LOW resistance, so inserting it in series barely affects the circuit's current — it simply lets all the current pass through while measuring it. A voltmeter is designed with very HIGH resistance, so connecting it in parallel draws only a tiny, negligible current, letting it measure potential difference without significantly altering the circuit it's measuring.
Real-Life Example
Why an ammeter connected in parallel could be dangerous
Accidentally connecting an ammeter in parallel (like a voltmeter) across a component can cause a dangerously large current to flow.
Because an ammeter has very low resistance, connecting it in parallel effectively creates a short circuit — a large, potentially damaging or dangerous current would flow through the ammeter, which is exactly why ammeters must always be connected in series.
Practice
How should a voltmeter be connected to correctly measure the potential difference across a resistor?
MediumCommon mistake
Mixing up which instrument goes in series and which goes in parallel — remember: Ammeter = series (low resistance, lets current through); Voltmeter = parallel (high resistance, measures difference without disrupting the circuit).
Quick Review
- Ammeter: measures current, connected in SERIES, has very low resistance.
- Voltmeter: measures potential difference, connected in PARALLEL, has very high resistance.
- Wrong connection (e.g. ammeter in parallel) can cause dangerous currents or inaccurate readings.