Voltage, Current and Resistance
The three quantities you measure every day, expressed in the way a car uses them.
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What you will learn
- Define voltage, current and resistance with correct units
- Describe electrical pressure and flow using the water analogy
- Choose the right meter function for each quantity
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Voltage is electrical pressure: the difference in potential between two points, measured in volts. Current is the flow of electrons, in amperes. Resistance opposes that flow and is measured in ohms. Think of a water circuit: voltage is the pump pressure, current is the litres per minute, and resistance is a narrow pipe.
In a car the battery supplies roughly 12.6 V at rest and the charging system raises the system voltage to about 13.8–14.6 V, but these are typical examples — always confirm with the manufacturer specification for the vehicle.
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| Quantity | Unit | Meter mode | Meter connection |
|---|---|---|---|
| Voltage | Volt (V) | DC volts | In parallel across the load |
| Current | Ampere (A) | DC amps | In series with the circuit |
| Resistance | Ohm (Ω) | Ohms | Component isolated, no power |
Measure voltage with the circuit energised, resistance with the circuit isolated. Reading resistance on a live circuit gives a meaningless number and can damage the meter.
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Key points
- Voltage is a potential difference (volts)
- Current is a flow rate (amperes)
- Resistance opposes current (ohms)
All values shown are training examples. Real thresholds depend on the manufacturer, engine, temperature and system — always confirm with the vehicle service documentation.
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