| English | Alternating current |
|---|---|
| Bahasa Melayu | Arus ulang-alik |
| 中文 | 交流电 |
Definition
An electric current that periodically reverses its direction of flow.
In exam terms
Alternating current (a.c.) is an electric current that periodically reverses its direction of flow. Current is measured in amperes (A).
On a current-time graph it appears as a wave that repeatedly crosses the time axis, so it flows first one way and then the other.
Its frequency is the number of complete cycles per second, measured in hertz (Hz); the Malaysian mains supply is about 50 Hz. Example of correct use: The 240 V, 50 Hz mains supply is an alternating current that reverses direction 100 times per second. Alternating current is used for mains electricity because its voltage can be changed easily by transformers.
Do not confuse it with…
Do not confuse alternating current with direct current (d.c.). Alternating current reverses direction regularly and its graph crosses the time axis; direct current flows one way only and stays on one side of the axis.
A transformer works only with a.c., because it needs a changing flux.
In Paper 2 this is asked as define or explain: define alternating current, or explain why a.c. rather than d.c. is used for transmission. When answering, link a.c. to its ability to have its voltage stepped up and down by transformers.
Source: DSKP KSSM Physics Form 4 and 5 (Versi English) (Bahagian Pembangunan Kurikulum (BPK), KPM)