Current, voltage and resistance
Current is the flow of charge round a circuit, measured in amps (A). Potential difference (voltage) pushes it, measured in volts (V). Resistance slows it down, measured in ohms (Ω). They are linked by V = I × R.
Key facts
- Current (A) is measured with an ammeter in series.
- Potential difference (V) is measured with a voltmeter in parallel.
- V = I × R
- Series: one loop, the same current everywhere. Parallel: branches; current splits.
Worked examples
Example 1
A 3 A current flows through a 4 Ω resistor. What is the potential difference across it?
- Multiply current by resistance. V = 3 × 4
- So V = 12 V
Answer: 12 V
Example 2
A 12 V battery is connected to a 6 Ω and a 2 Ω resistor in series. What current flows?
- In series, add the resistances. 6 + 2 = 8 Ω
- Rearrange V = IR. I = 12 ÷ 8 = 1.5 A
Answer: 1.5 A