Need help understanding AC currents (1 Viewer)

[EkGew]

I have asked my teacher a few times, and all those times he has just started explaining and then rambled of about something else.
My problem is that i do not understand the way AC current works, just don't get it.
I get DC jsut goes around the circuit, recharging (changing back to negative) at the power and starting again. But AC has got me stumped.

Thanks in advance.

 

[Not-That-Bright]

Well you see, AC is alternating current.

The picture below should help you. Note that the blurred lines of the city lights are not straight but are instead dotted - this is because of Alternating Current.

 

[EkGew]

Well you see, AC is alternating current.

The picture below should help you. Note that the blurred lines of the city lights are not straight but are instead dotted - this is because of Alternating Current.

http://upload.wikimedia.org/wikipedia/commons/thumb/4/42/City_lights_in_motion.jpg/800px-City_lights_in_motion.jpg

That is my problem, i don't get why it is alternating. Just don't get the point of it, and what advantages are of using it. I know about Westinghouse and that...never got it, due to this problem.

 

[Not-That-Bright]

oh ok, as far as I know some advantages are:

- voltage can be increased to higher levels through a transformer
- sent farther distances through high tension wires,
- and the voltage can be lowered when it's reached its destination.

http://en.wikipedia.org/wiki/War_of_Currents

 

[EkGew]

Thanks Not-That-Bright, but thats not exactly what im looking for, the info you gave me is also nice.

What i am actually trying to find out is, why alternating current..is alternating current. Why not use DC current (why cant it be used in Transformers) for everything instead.

Sorry to be a pain, thanks!

 

[velox]

Cos with DC current you cant step it down or up very easily, hence big transmission loss, hence power stations need to be located near sydney etc...

 

[helper]

Alternating current means the current will flow in one direction and then the opposite direction. This change occurs 50 times a second.

For a transformer to work there needs to be a change in magnetic flux. The easiest way to change a flux is to increase or decrease the current, which is occuring in AC, so it can be transformed.

DC is a constant or has small changes in magnitude, so can't be readily transformed. There are DC transformers but they run one turning the current on and off, so are not practical for most devices. You induction coil at school would be an example of a DC transformer. IT has an electromagnet that turns on and off the current.

 

[EkGew]

Ok, i understand, but since it goes back and forth, how does it power things (so does an electron go through something, then in 1 hertz, turns around and comes back through the obejct?) (object = whatever it is powering)

 

[fush]

as said before AC current is an alternating current. The electron flow (current) switches direction 50 or 60 times a second. That is they travel through the circuit then back through it the opposite way.

This alternating current creates a change in magnetic flux which allows the use of transformers.

Transformers are the main reason AC is preferred over DC. By using AC current, the voltage can be stepped up for electricity distribution over long distances and then stepped down again at sub stations ( using transformers) for household use.

Most appliances in a home run at 240V, however it would be highly inefficient to distribute current at this voltage due to high power losses given by the formula P = I^2R (where P is pwer loss, I is current, and R is the resistance of the power line).

Hence to reduce power losses it is preferred to have higher voltages for transmission. The only way to step up and down power is with the use of transformers which require an alternative current to work.

therefore, AC is the go

 

[EkGew]

as said before AC current is an alternating current. The electron flow (current) switches direction 50 or 60 times a second. That is they travel through the circuit then back through it the opposite way.

This alternating current creates a change in magnetic flux which allows the use of transformers.

Transformers are the main reason AC is preferred over DC. By using AC current, the voltage can be stepped up for electricity distribution over long distances and then stepped down again at sub stations ( using transformers) for household use.

Most appliances in a home run at 240V, however it would be highly inefficient to distribute current at this voltage due to high power losses given by the formula P = I^2R (where P is pwer loss, I is current, and R is the resistance of the power line).

Hence to reduce power losses it is preferred to have higher voltages for transmission. The only way to step up and down power is with the use of transformers which require an alternative current to work.

therefore, AC is the go

That is excellent information, backing up the others, but i am still not understanding the one thing...how does it actually power things up, if the electron is going back and forth...

 

[fush]

ok, for example imagine a small light globe in a circuit creating resistance in the form of light and heat. As the electrons travel back and forward in the circuit they hit the light globe creating that resistance,hence poweing the light globe.

Other examples may include a small electric fan which spins at 60 times a second since it is powered by AC current.

 

[EkGew]

ok, for example imagine a small light globe in a circuit creating resistance in the form of light and heat. As the electrons travel back and forward in the circuit they hit the light globe creating that resistance,hence poweing the light globe.

Other examples may include a small electric fan which spins at 60 times a second since it is powered by AC current.

Thanks alot! That is what i was looking for, i couldn't work out how it was powering things!

 

[M-turkey]

Also, just because electrons are going back and forth, does not mean they arent doing anything.

Most of the time, the AC current is converted into DC current anyways. If you look at computers, TVs and many other electrical devices that come with a transformer with them, they also contain something similar to whats called a diode bridge, basically it changes AC so it acts like DC.

Looking at my laptop transformer it has a 240 V AC input and a 18.5 V DC output.

What I'm trying to say is AC is more efficient for transmission from the power plant to your home, but many devices convert it to DC anyways.