Electricity (GCSE Physics)

Hello, i would like to know what's the difference between AC (alternative current) and DC (direct current) electricity? why use AC instead of DC or the other way round can anyone tell me the advantages and disadvantages of each if possible please

Thanks a lot for your time

From John Wood

Reply 1

john !!

with alternative current, the direction of the flow of charge is switched 50 times a second, so you have the electrons going forward, then back, then forward, etc.

direct current just has the charge going the same way.

You would use alternating current for specific reasons, such as with electromagnets if you want something to vibrate with a time period of 0.02 s, eg. a ticker timer.

I think we use AC in the UK and they use DC in Europe, so when the Eurostar goes under the channel it has to switch power supply and convert AC to DC. If you know what a diode is can you think of a way to convert AC to DC? (there is a neat circuit arrangement!)

Reply 2

cosmik_debris

DC is not used in europe or anywhere in the world (the west at least), its too impractical.

Firstly the generation of ac is a lot simpler than dc and secondly only ac can work a transformer. If you consider your mains supply, the chances are that you live some distance away from the generator which supplies your electricity. If the generator supplied dc then all power would be lost in a short time as it traveled along the distribution line. By using much higher voltages (40,000 volts) the loses are much reduced but, of course, having this voltage entering the home would be dangerous and so a transformer is used. Transformers are able to step down the voltage and so these are used to reduce the voltage for the final leg of the journey to your home. (Note the mains electricity is distributed at these very high voltages but at low current and so the distribution wires do not heat up greatly).

Even with the use of a full-wave bridge rectifier (that arrangement of diodes), you still have a dirty supply and so need to perform what is called 'smoothing' and more often than not 'regulation'.

Reply 3

john !!

well that sure beats my answer!

Reply 4

Morbo

I'm pretty sure AC is "alternating current". And transmission lines on the pylons that run the length of the country are more around 400 000V.

Reply 5

cosmik_debris

Worzo

I'm pretty sure AC is "alternating current". And transmission lines on the pylons that run the length of the country are more around 400 000V.

You're right, a missing a 0. :redface:

Reply 6

Alcohol5%

Definately, AC is alternating current because it alternates from the positive to the negative.

Reply 7

rachelrainbow32

do we really have to know all that for the exam

Reply 8

cosmik_debris

You should know:

- What does AC and DC stand for?
- What is the difference between AC and DC?
- When and why are AC currents more useful than DC currents, and vice versa.

:smile:

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