**Alternating Current (AC):**

- The voltage of alternating current fluctuates continually:
- In Hong Kong the frequency of this fluctuation is 50 hertz which means 50 cycles per second.
- Thus meaning that whenever the sine curve crosses the x axis the current is switched off and the wires are allowed to cool to prevent overheating.
- This allows one to transport much more electricity than one would be able to with a wire carrying direct current.
- Remember that temperature and resistance are proportional.

Graph from http://physics.stackexchange.com/questions/41779/why-do-we-use-root-mean-square-rms-values-when-talking-about-ac-voltage (Crazy Buddy)

- It is possible to work out how much heat a transmission of AC current produces in a wire relative to the heat produced by a transmission of DC current by working out the Root Mean Square (RMS):

- Peak voltage (VP) is the maximum voltage that the sine curve reaches.
- Take the graph above (y-axis is voltage and x-axis is time), the RMS (indicated by the dotted line) is 0.707.
- This means that a 1V alternating current only produces the same amount of heat energy during transmission as a 0.707V direct current.
- This might not seem like much, but at high voltages, this could mean millions of dollars worth of electricity!

- This can be generated by generators.
- However, since many electronic components are polarised, this current is useless, even destructive in all but the simplest components:
- Therefore it must be converted into direct current for the electricity to be usable in circuits.
- Lamps, though can used AC.
- And transformers can only function on AC.

**Direct Current:**

- The voltage of steady direct current does not fluctuate and so is always constant as you can see in the graph below:
- The current direction does not change.
- But because of this it is difficult to transmit as it generates more heat energy than AC.

- The current direction does not change.
- The voltage of smooth direct current does fluctuate somewhat but the current direction remains constant:
- It has a small variation or ripple.

- It can be generated by:
- PV panels:
- Photovoltaic panels (i.e. solar panels).

- Batteries.
- DC generators (dynamos).

- PV panels: