Lesson 6 of 14
Two kinds of current
Show on a big screenA cell pushes current one way. The supply in your home keeps reversing its direction.
In the picture, the axis is the middle line. The current is zero there. A cycle goes from one direction to the other and back.
Step 1 of 3
- Direct current: a flat line. It keeps one direction.
- Alternating current: a wave, crossing the axis and back.
- One complete cycle has two direction reversals.
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The rule
Direct current keeps one direction. Alternating current reverses direction again and again. Frequency is the number of cycles in one second, in hertz. In India the supply is alternating current at 50 Hz.
- Direct current (DC): flows one way only. A cell gives it.
- Alternating current (AC): reverses direction at a steady rate.
- Frequency: cycles per second, in hertz (Hz).
Worked example
Each cycle has two reversals. So the reversals in one second are 2 × frequency.
| Frequency | Reversals in one second |
|---|---|
| 10 Hz | 20 |
| 25 Hz | 50 |
| 50 Hz | 100 |
A 50 Hz supply has 100 reversals in 1 second. At 50 Hz the current reverses every 1/100 of a second.
AC can be sent over long distances. Little energy is lost on the way.
Try the lab to finish this lesson.