Describe AC to me in terms of electrons

[foges]

Ok, this is probably an easy question, but whatever.

In highschool physics we pretty much learned that in AC the power and voltage take a sinusodal form. Which im assuming is just a constant change in direction of the electron flow. As in 50 times per second the power generator pulls the electrons in the wire to it and 50 times a second it pushes them away. And that would also mean that all the electrons in the wire connected to the generator are either pulled to the generator or pushed away from it. But how does that work: how is the high/low electron density created at the generator effectively reflected perfectly many kilometers away at my wall socket (ignoring transformers, etc...)? its not as if electrons are connected to eachother in a long metal rod! As i understand it there would be a high or low electron density at the generator which fades away as the wire got longer. Im also taking into account that the drift velocity of electrons is to the order of millimeters/second, so they cant exactly rush back and forth to the generator and back to my wall socket (which is guess is the point of AC).

Anyways, i hope im not too confusing, i probably am. Unfortunatelly my highschool physics teacher hated electronics

 

[Born2bwire]

An electromagnetic wave is generated that travels (or sets up as a standing wave more accurately) along the length of the transmission line. The electric field component of the wave is what oscillates the electrons back and forth. There is a secondary electric field generated from the changing magnetic field and so on and so on.

So when it comes to electric circuits, you're not transmitting electrons, but electromagnetic waves which cause the mostion of the electrons. This is why the signal propagates at speeds much higher than the drift and saturation velocities. It's only when you need to set up voltages and charges, like in a transistor, that the details of the speed and amount of charges that are flowing are relevant.

 

[Aluvus]

Wiggle wiggle wiggle.

 

[soccerballtux]

Ya born is right. An easy way to think of it-- take that sinusoidal wave you see? Turn that vertical. As time increases (you start at the top and go down), that is the representation of the electron's position in any part of the wire. They just go back and forth.

 

[hellokeith]

Electron flow is actually opposite the logical flow of voltage/current. But engineers typically don't deal with actual electron flow.

 

[jagec]

Originally posted by: foges
Ok, this is probably an easy question, but whatever.

In highschool physics we pretty much learned that in AC the power and voltage take a sinusodal form. Which im assuming is just a constant change in direction of the electron flow. As in 50 times per second the power generator pulls the electrons in the wire to it and 50 times a second it pushes them away. And that would also mean that all the electrons in the wire connected to the generator are either pulled to the generator or pushed away from it. But how does that work: how is the high/low electron density created at the generator effectively reflected perfectly many kilometers away at my wall socket (ignoring transformers, etc...)? its not as if electrons are connected to eachother in a long metal rod! As i understand it there would be a high or low electron density at the generator which fades away as the wire got longer. Im also taking into account that the drift velocity of electrons is to the order of millimeters/second, so they cant exactly rush back and forth to the generator and back to my wall socket (which is guess is the point of AC).

Anyways, i hope im not too confusing, i probably am. Unfortunatelly my highschool physics teacher hated electronics

If you line up a whole bunch of kids right next to each other, and shove one end, the kid on the other end will fall over, even though none of the kids moved very far. Try this sometime.

 

[KIAman]

Water in a pipe... but the pipe is prefilled with water and there are no leaks.

 

[silverpig]

Originally posted by: KIAman
Water in a pipe... but the pipe is prefilled with water and there are no leaks.

Yup. Current flow is very similar to water in a pipe. Imagine a pump pushing the water back and forth. The molecules themselves don't go very far, but the pressure wave is felt throughout the whole pipe.

 

[firewolfsm]

So...rather than looking it up, is 120V AC actually equivalent in voltage to 60V DC?

 

[Special K]

Originally posted by: firewolfsm
So...rather than looking it up, is 120V AC actually equivalent in voltage to 60V DC?

Equivalent in what sense of the word? You can convert a sinusoidal voltage source given as Vpeak (peak voltage, that is, the maximum voltage the signal attains) to an RMS voltage by dividing the amplitude (Vpeak) by sqrt(2). This RMS voltage would produce the same power dissipation in a resistor as a DC voltage source of the same value would.

So for your example:

120 Vpeak / sqrt(2) = 84.85 Vrms.

Incidentally, the 120VAC of household power is actually an RMS value, not a peak value. The voltage oscillates between +/- 170V. Dividing this by sqrt(2) is approximately 120 V.

When capacitors and inductors are present in the circuit, then you can't really make any equivalence between an AC source and a DC source, because the current and voltage of a capacitor an inductor are not in phase with each other, assuming the circuit is connected to an AC source.

 

[BrownTown]

In terms of power output 120V AC = 120V DC, the reason that AC is reported in RMS is so that the two will be equal to each other even though the AC is really going +-170 like someone else already said.

 

[jhu]

Originally posted by: silverpig

Originally posted by: KIAman
Water in a pipe... but the pipe is prefilled with water and there are no leaks.

Yup. Current flow is very similar to water in a pipe. Imagine a pump pushing the water back and forth. The molecules themselves don't go very far, but the pressure wave is felt throughout the whole pipe.

now imagine modern computing, but with water...

 

[BrownTown]

Originally posted by: jhu

Originally posted by: silverpig

Originally posted by: KIAman
Water in a pipe... but the pipe is prefilled with water and there are no leaks.

Yup. Current flow is very similar to water in a pipe. Imagine a pump pushing the water back and forth. The molecules themselves don't go very far, but the pressure wave is felt throughout the whole pipe.

now imagine modern computing, but with water...

now imagine it with nothing but light!

 

[jhu]

Originally posted by: BrownTown

Originally posted by: jhu

Originally posted by: silverpig

Originally posted by: KIAman
Water in a pipe... but the pipe is prefilled with water and there are no leaks.

Yup. Current flow is very similar to water in a pipe. Imagine a pump pushing the water back and forth. The molecules themselves don't go very far, but the pressure wave is felt throughout the whole pipe.

now imagine modern computing, but with water...

now imagine it with nothing but light!

i still like my water idea better