Overview
The lecture explains the difference between alternating current (AC) and direct current (DC), their sources, characteristics, and how voltage changes over time.
Alternating Current (AC)
- Alternating current (AC) is when the current changes direction back and forth repeatedly.
- AC is produced by an alternating potential difference (voltage) that fluctuates between positive and negative values.
- On a potential difference vs. time graph, AC shows a regular pattern switching between positive and negative.
- In the UK, mains electricity is AC at 50 hertz (Hz) and around 240 volts (can also be referred to as 230 volts).
- The potential difference in UK mains supply changes from +240V to -240V fifty times per second.
- The direction and size of the AC current also change at this same rate.
Direct Current (DC)
- Direct current (DC) flows in one direction only.
- DC is produced by a direct potential difference, which stays positive or negative throughout.
- Examples of DC sources include cells and batteries found in devices like phones and calculators.
Measuring Current and Potential Difference
- Oscilloscopes are devices used to display potential difference vs. time graphs for AC and DC.
Key Terms & Definitions
- Alternating Current (AC) — electric current that repeatedly reverses direction.
- Direct Current (DC) — electric current that flows in only one direction.
- Potential Difference (Voltage) — the difference in electric potential energy between two points in a circuit.
- Oscilloscope — an instrument that shows how voltage changes over time.
- Hertz (Hz) — unit of frequency, representing cycles per second.
Action Items / Next Steps
- Review differences between AC and DC and how each appears on oscilloscope graphs.
- Remember the UK mains supply values for potential difference and frequency.