Multimeter simulator
A digital multimeter to practise choosing the right function and range, reading the display, and converting the units and prefixes. It's free to use, with no sign-up.
Question
Use the multimeter, connected as an ammeter, to measure the current through an LED in a DC circuit. It is expected to be about 50 mA.
Turn the dial by clicking a setting. After clicking it, the left and right arrow keys step round it too. The display shows what the real meter would, but not the unit: work that out from the setting. Then enter the reading, and choose its unit.
How to choose the setting
- Choose the function: V DC for a cell, battery or power pack, V AC for an alternating supply, A DC for current, Ω for resistance.
- Choose the range: the smallest one that is bigger than the value you expect. If the display shows a 1 on its left, it is overloaded: turn up to a bigger range.
- Connect it correctly: an ammeter goes in series with the component, a voltmeter in parallel across it, and a resistor must be out of the circuit when you measure its resistance.
The number on the dial is the largest reading the range can show. On the 200 range, a 3.2 V reading would be shown as 3.2 V, but only to one decimal place; on the 20 range it shows 3.20 V, with an extra digit.
Reading the display and prefixes
The display shows only digits (and AC or DC). The unit comes from the dial setting: the letter after the number on the dial is a prefix for that function's unit.
- V DC: 200m and 2000m read in mV; 20 and 200 read in V.
- A DC: 200µ reads in µA; 200m reads in mA; 10 reads in A.
- Ω: 200 and 2000 read in Ω; 20k and 200k read in kΩ; 20M reads in MΩ.
The letters in a unit are prefixes:
| Prefix | Meaning | Example |
|---|---|---|
| µ (micro) | × 10⁻⁶ | 150 µA = 0.000 150 A |
| m (milli) | × 10⁻³ | 45 mA = 0.045 A |
| k (kilo) | × 10³ | 4.7 kΩ = 4700 Ω |
| M (mega) | × 10⁶ | 1.2 MΩ = 1 200 000 Ω |
On the dial, "2000m" on a voltage range means 2000 mV, which is 2 V. A lower-case m is milli and an upper-case M is mega, a factor of a billion apart, so check which you have.
Common mistakes
- Forgetting that the unit depends on the dial setting, and reading 45.2 mA as 45.2 A.
- Confusing m (milli) and M (mega), or µ (micro) and m (milli).
- Choosing AC instead of DC, which reads zero for a DC source.
- Using a range that is far too large, which loses digits and increases the percentage uncertainty.
- Connecting an ammeter in parallel, which can blow its fuse.
Frequently asked questions
- How do you choose the right range on a multimeter?
- Use the smallest range that is bigger than the value you expect. It shows the most digits, so the smallest percentage uncertainty. If the display shows a 1 on the left, it is overloaded: choose a bigger range.
- What does the 1 on the left of a multimeter display mean?
- It means overload: the value is too big for the range you have chosen, so turn the dial to a bigger range.
- What do m, µ, k and M mean on a multimeter?
- m is milli (a thousandth), µ is micro (a millionth), k is kilo (a thousand) and M is mega (a million). So 45 mA is 0.045 A and 4.7 kΩ is 4700 Ω.
- How do you connect a multimeter to measure current and voltage?
- Connect it in series with the component to measure current, and in parallel across the component to measure potential difference.
Practise it in a full required practical
LabWizard walks A-Level Physics students through simulated required practicals, from taking measurements with instruments like this one to graphing, analysis and exam questions. This skill is used in the EMF and Internal Resistance, Resistivity of a Wire practicals.
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