Electric current is the flow of electric charge. It can flow in two ways.
Direct current (DC)
The current flows in one direction only, at a steady level.
- Batteries, solar panels, phones, laptops and almost all electronics run on DC.
Alternating current (AC)
The current changes direction back and forth many times a second. The number of full back-and-forth cycles per second is the frequency.
- Canada and the USA use about 120 V at 60 Hz at the wall socket.
- Nepal, India and most of Europe use about 230 V at 50 Hz.
Why the grid uses AC
AC voltage is easy to raise and lower with a transformer. Power stations raise the voltage very high for long-distance lines (less current, so less energy lost as heat), and transformers near your home bring it back down.
Why your charger is warm
Your phone needs low-voltage DC, but the wall gives AC. The charger converts AC to DC and lowers the voltage. Some energy becomes heat in that process.
| DC | AC | |
|---|---|---|
| Direction | One way | Changes many times a second |
| Typical source | Battery, solar panel | Wall socket, generator |
| Used for | Electronics, cars, phones | Homes, factories, the grid |
Safety: mains AC can kill. Learn on low-voltage DC (a 9 V battery and an LED) before ever working near a wall socket.