# AC

Discussion in 'Homework Help' started by Cerkit, Oct 3, 2010.

1. ### Cerkit Thread Starter Senior Member

Jan 4, 2009
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Why is there a need for a return conductor in AC?? If I just connect a single conductor supplied with AC to a light bulb the electrons are moving back and forward so why isn't this enough to make the bulb light??

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2. ### R!f@@ AAC Fanatic!

Apr 2, 2009
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think of it as a roller coaster. Every Power source needs a supplier and a collector, thus two wires.
One to force current out....do the job.....and another to collect the current when it returns

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3. ### Cerkit Thread Starter Senior Member

Jan 4, 2009
286
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Your explanation makes sense for DC but not for AC...

4. ### Georacer Moderator

Nov 25, 2009
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Here the analogy of the water pump comes in handy.

Imagine your electrical wire network as a loop of water tubes. The source is a water pump. The load (lamp or watever) is a toy-watermill you want to see moving.

The tubes are filled with stationary water. If the tube loop is not complete, for example it goes at a straight line with a closed valve at the end, with no return, then the valve won't be able to push nor pull water into or from the tubes. Thus it can't work neither in DC nor AC operation.

You need to close the tube network and guide it around to meet the pump again in order for it to be able to pump water continuously (DC) or push and pull (AC).

Electrons behave pretty much the same. They can't leave an area unless others come to replace them. They can't be crowded in an area, their density is fixed for a given material. In order to produce work and circulate around the network they need a way to get back to the source that provides the motive force.

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5. ### R!f@@ AAC Fanatic!

Apr 2, 2009
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IN DC, current flows in one direction only.

In AC Current flows forward and backward. Speed is determined by the Frequency.
Which means, if say 50Hz. 50Hz Applies that Current Alters ( which means goes positive and then goes negative) 50 times with in a second.

6. ### beenthere Retired Moderator

Apr 20, 2004
15,808
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Think about a circuit. If the lamp only has one conductor led to it, then the voltage varies from the negative peak value to the positive peak value 50 times/second. No current flows, though - only the potential that would cause current if a circuit existed.

7. ### BillB3857 AAC Fanatic!

Feb 28, 2009
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As I read this, I am also listening to the radio. The signal I get it AC, right? No wires at all between me and the station.

8. ### zgozvrm Active Member

Oct 24, 2009
115
3
(Note: Although not entirely correct, this post describes electrical flow without getting into the messy details)

Think of a hose with the end plugged off; it can't do any work unless the water is allowed to flow. With the end plugged, you can't push water through the hose, nor can you pull it out (due to the vacuum created).

A DC battery basically supplies (pushes) electrons to the circuit from one of it's terminals. As the electrons travel through the circuit, they displace other electrons, which displace still other electrons. Eventually there will be an excess of electrons at the other end of the circuit. Since electrical current (at low voltage levels) can't flow through the air, it needs a place to go. The battery receives them at the other terminal.

An AC generator works basically the same way; it pushes electrons through the circuit from one terminal and receives the excess on the other terminal. Then the flow is reversed.

So, having a single wire is kind of like having a plugged off hose; it can't do any work because it effectively blocks the flow of electrons.

That's about as simple an explanation as I can come up with right now.

9. ### zgozvrm Active Member

Oct 24, 2009
115
3
Apples and oranges: radio waves and sound waves can travel through the air, whereas AC current (at typical usable levels) cannot.