Ammeters and voltmeters are two of the most commonly used instruments in science education and electrical testing, yet they are frequently confused. Both help explain how a circuit behaves, but they measure different quantities and must be connected differently to give an accurate reading. Livingstone’s ammeters are designed to measure electric current, while its voltmeters measure electric potential difference. Knowing which instrument to use, and how to connect it correctly, is a foundational skill for students, science educators and laboratory technicians alike.
What Is an Ammeter and What Does It Measure?
An ammeter measures electric current, expressed in amperes, at a specific point in a circuit. It is connected in series so the current being measured flows directly through the instrument, and it has very low internal resistance to avoid affecting the circuit it is testing.
Because an ammeter carries the full current of the circuit branch it is connected to, it is built with minimal internal resistance so it disrupts normal circuit operation as little as possible. If an ammeter is mistakenly connected in parallel across a component, it can create a short circuit, since its low resistance offers current an easy path, potentially damaging the meter.
What Is a Voltmeter and What Does It Measure?
A voltmeter measures the potential difference, or voltage, between two points in a circuit, such as across a battery or resistor. It is connected in parallel and has very high internal resistance, so it draws minimal current away from the circuit.
This high internal resistance is intentional. By limiting the current that flows through the meter itself, the instrument avoids altering the voltage it is trying to measure, which is why a voltmeter is always placed across, rather than within, the part of the circuit being tested. Connecting it in series instead restricts current flow and produces a reading that does not reflect normal circuit behaviour.
How Do Ammeters and Voltmeters Measure Electrical Quantities Differently?
The key difference between an ammeter and a voltmeter is what they measure and how they connect to a circuit: an ammeter measures current in series, while a voltmeter measures potential difference in parallel.
An ammeter’s low resistance lets it sit within the current path without restricting flow, while a voltmeter’s high resistance lets it sit across two points without drawing meaningful current. This is why an ammeter is generally used to measure current through a specific component or circuit branch, while a voltmeter is used to measure voltage across a battery, resistor or other component. The most common error with either instrument comes from reversing the connection method: an ammeter in parallel can short-circuit the meter, while a voltmeter in series will restrict current flow and produce an inaccurate reading.
Why Does Circuit Connection Matter So Much?
Correct connection is critical because each instrument is designed around a specific resistance level, and only gives an accurate, safe reading when connected the way it was designed to be used.
An ammeter wired in parallel behaves like a short circuit, drawing excessive current and risking damage to the meter. A voltmeter wired in series behaves like an open circuit, since its high resistance blocks normal current flow, giving a reading close to zero or the full source voltage rather than a meaningful measurement. This distinction, series for current and parallel for voltage, is one of the first practical skills taught in circuit theory, and it underpins safe handling of electrical test equipment more broadly (SafeWork NSW 2023).
When Should You Use an Ammeter or a Voltmeter?
An ammeter is the right choice for finding out how much current is flowing through a specific part of a circuit. A voltmeter is the right choice for comparing electric potential between two points.
Use an ammeter to verify that a component is operating within its rated current, diagnose whether a circuit branch is drawing more or less current than expected, or teach students how current behaves across series and parallel branches. Use a voltmeter to check that a power supply or battery is delivering its rated voltage, measure the voltage drop across individual components, or confirm a circuit is receiving the expected supply before further testing.
Can one instrument measure both current and voltage?
A multimeter can measure both, along with resistance, by switching functions and connection methods. Dedicated ammeters and voltmeters remain popular in teaching settings because their single, clear function helps students grasp the underlying concept without added complexity.
What happens if a voltmeter is connected in series by mistake?
It’s very high internal resistance will severely restrict current flow, so the circuit effectively behaves as though it is open, and the reading will not reflect normal operating conditions.
What happens if an ammeter is connected in parallel by mistake?
It’s very low internal resistance can create a short circuit path, causing a current surge that may damage the meter or the component it is connected across. Ammeters should always be connected in series.
Are ammeters and voltmeters accurate enough for professional testing?
Accuracy depends on the quality of the instrument and how well it is maintained. Instruments used for calibration, trade or professional testing in Australia are assessed against national measurement standards maintained by the National Measurement Institute (National Measurement Institute 2025), and electrical test equipment used in workplaces should be inspected regularly in line with national work health and safety guidance (SafeWork NSW 2019).
Ammeters and voltmeters each play a distinct role in understanding circuit behaviour. Knowing what each measures, how it should be connected, and why that connection matters helps ensure accurate readings and safer handling, whether in a school laboratory, a technical workshop or a professional testing environment.
References
SafeWork NSW 2023, Electrical inspection and testing, NSW Government, viewed 20 August 2026, <https://www.safework.nsw.gov.au/hazards-a-z/electrical-and-power/electrical-inspection-and-testing>.
SafeWork NSW 2019, Managing electrical risks in the workplace: code of practice, NSW Government, viewed 20 August 2026, <https://www.safework.nsw.gov.au/__data/assets/pdf_file/0010/50230/Managing-electrical-risks-in-the-workplace-COP.pdf>.
