AC theory

Darkwood · Jan 30, 2012

As mentioned already its a big misbelieve that electrons wizz around the circuit and also that current flows positive to negative (DC is negative to positive) ... i read up on quantum theory alot and to explain in simple terms the electrons in A/C dont really move more vibrate left and right where as in DC the migrate at a very slow pace in the order of several meters per minute, what is actually happening is the propergation of the electron field cloud which will be close to the speed of light and its this that does the business end of the circuit, f your interested i could explain how this works as it can get all confusing very quickly but using everyday ref' it can be understood.

Richard Burns · Jan 30, 2012

Just my thoughts on the matter:
A current will flow if there is a potential difference between two points connected by a conductor.
Whilst a current flow is speed of light (ish) it is the transfer of a charge along the conductor, this is not the same as movement of electrons,
In a DC circuit you have a positive with a potential difference from the negative so current will flow.

Here you are considering a circuit that is connected from the line supply to the neutral.
In an AC circuit the line conductor has a sinusoidal value of potential difference with respect to the neutral.
The peak voltage is 325V (ish), the actual nominal sign (+ or -) of the potential difference is immaterial it is still a potential difference with relation to our nominal (approximate zero value) of the neutral.
At the start of a cycle there is no potential difference and no current flows, as the potential difference rises up the first peak current increases to maximum when the potential difference reaches 325V, and then starts to decrease as the peak drops back to zero. The potential difference (a difference not a value) then starts to increase in the opposite direction and current flows in the opposite direction rising to a new maximum at (-ve)325V. Repeat 50 times per second.

Where you have a resistance in a circuit then there is a voltage drop across that resistance that is proportional to the resistance.

If you think of a line and neutral supply connected by cable to a lamp.
There is a very low resistance in the line conductor, a relatively high resistance in the lamp and a very low resistance in the neutral conductor.
The voltage drop from the start of the supply (230V rms) to the end of the neutral (approx 0V) is of course 230V rms.
The voltage drop in the line conductor will be very small (for example say 4V) as the resistance is very low, the voltage received at the lamp will now be 226V rms. Assuming that the neutral conductor is the same csa and length as the line conductor this will also drop 4Vrms, so therefore the lamp will drop 222V rms to give a total volt drop of 230V rms.
This means that on exiting the lamp the voltage is at a maximum 4V, which you will not feel, so you will not get a (noticeable) shock.
If you disconnect the neutral from its connection to earth and hold the neutral cable as it exits the lamp, you are now a very high resistance connected in the circuit (if you are connected to earth in any way). The total volt drop to earth must still be 230V rms, however you will provide the maximum volt drop as the largest resistance in the circuit so at the exit from the lamp it will be much closer to 230V and you can definitely feel this!

Knobhead · Jan 30, 2012

Here’s one for the more intrepid (bonkers) members to try. (I take No responsibility for death or injury if you try it).

View attachment 10351
This system is used in photographic studio flash units. I calculated one of my 1000 joule units could punch out 650V at 400A for < 100[SUP]th[/SUP] second

Andy 7671 · Jan 30, 2012

Fascinating read,

electron field cloud..gonna throw that one in at work tomorrow..

Dash..was the cat a ghost or did it live in the end...?

La Poste is now trawling Amazon looking for more books

i=p/u · Feb 1, 2012

la poste maybe opened his lamp and touched the line conductor..... but this shows you how little i knw

Mark42 · Feb 1, 2012

Andy 7671 said:
... Dash..was the cat a ghost or did it live in the end...?

Schrödinger’s cat neither lived nor died, it did both, at the same time, forever existing in a superposition of states.

If I remember right, there was some kind of infernal contrivance which released poison if a particular radioactive atom decayed. It was a thought experiment offered as an illustration of the weirdness of the tiny quantum world, when applied to the macroscopic world in which we all live.

The particle in question had been interacted with another kept in the lab, but in accordance with the quantum principle of entanglement, neither existed in any particular state, ie their wave function was ‘smeared’ until this attribute - called Psi - collapses into a definite state on observation. So you never know if the cat is alive or dead until you open the box and look. So until you do, it’s both.

Weird eh?

That’s as far as I understand it. I’m no physicist: I was having trouble getting volt drop calcs right this morning!