Alternating current is electricity that changes direction periodically, just like the waves in the ocean. It’s the type of current that powers your phone charger, TV, and most household appliances.
The two are inversely related:
\$f = \frac{1}{T} \quad \text{and} \quad T = \frac{1}{f}\$
Example: In the UK, mains electricity has a frequency of 50 Hz.
\$T = \frac{1}{50\,\text{Hz}} = 0.02\,\text{s} = 20\,\text{ms}\$
Most appliances are rated in RMS (Root Mean Square) values because RMS gives the equivalent DC power. For a sinusoidal wave:
\$V{\text{peak}} = \sqrt{2}\,V{\text{RMS}}\$
So a 230 V RMS mains supply has a peak voltage of:
\$V_{\text{peak}} = \sqrt{2}\times 230\,\text{V} \approx 325\,\text{V}\$
| Country | Frequency (Hz) | Period (ms) |
|---|---|---|
| UK / Europe | 50 | 20 |
| USA / Canada | 60 | 16.7 |
| Japan | 50 | 20 |
\$T = \frac{1}{60} \approx 0.0167\,\text{s} = 16.7\,\text{ms}\$
\$V_{\text{peak}} = \sqrt{2}\times 230 \approx 325\,\text{V}\$
\$T = \frac{1}{100} = 0.01\,\text{s} = 10\,\text{ms}\$
Answer the following in the comments or on your worksheet:
- The period tells us how long one cycle takes.
- The frequency tells us how many cycles happen each second.
- The peak value is the maximum voltage or current in a cycle.
- RMS values give us a convenient way to compare AC power to DC.
- Knowing these terms helps you understand how electricity powers everyday devices.