Trying to understand electricity

Softshoulder

I'm trying to get my head around how electricity flows in a circuit.

Can someone explain it?

Is this correct? Current flows on live into item to power it. The "used electricity" flows on the neutral.

From there I am stuck. Does the neutral flow into the earth somewhere in a house or does it go back on a power line to somewhere?

2011

Softshoulder wrote: »

I'm trying to get my head around how electricity flows in a circuit.

It will flow between different potentials if a suitable conductor connects them. Think of it like air flow between tanks that are at different pressures connected by a pipe.

Is this correct? Current flows on live into item to power it. The "used electricity" flows on the neutral.

An electrical current will flow through an electrical load to “power it”.
A local transformer supplies your home with electrical power. The current flows from this on the phase conductors (live wires) and returns to the transformer on the neutral conductor.

From there I am stuck. Does the neutral flow into the earth somewhere in a house or does it go back on a power line to somewhere?

The neutral is connected to earth at the transformer and generally at the house too. This means that there is an alternative return path to the transformer through the earth. Under normal conditions only a small current flows though the earth. Under fault conditions a larger earth current may flow.

coylemj

Alternating current (AC) involves push and pull, the cycle is repeated 50 times a second with the mains feed you have in your house. The live terminal pushes out the current, then pulls it back again. By raising the voltage into positive, then back to zero, then into negative, then back to zero. Neutral completes the circuit but is otherwise passive i.e. it's the live terminal that does the work.

It sounds far more complicated than direct current (DC) where the current only flows in one direction, this is what you have in simple battery-driven appliances but unlike DC, the voltage of alternating current can be modified by transformers. Which makes it easier to distribute at high voltage over long distances, then step down the voltage for domestic distribution.

https://en.wikipedia.org/wiki/Alternating_current

CoBo55

Tesla would be turning in his grave at those descriptions, Edison would be happy though...

Not you coylemj...
With the exception of most white goods everything else runs on DC (rectified internally but DC nonetheless)

Softshoulder

coylemj wrote: »

Alternating current (AC) involves push and pull, the cycle is repeated 50 times a second with the mains feed you have in your house. The live terminal pushes out the current, then pulls it back again. By raising the voltage into positive, then back to zero, then into negative, then back to zero. Neutral completes the circuit but is otherwise passive i.e. it's the live terminal that does the work.

It sounds far more complicated than direct current (DC) where the current only flows in one direction, this is what you have in simple battery-driven appliances but unlike DC, the voltage of alternating current can be modified by transformers. Which makes it easier to distribute at high voltage over long distances, then step down the voltage for domestic distribution.

So I know AC changes direction, but let's take one single electron changing direction in a cable 10m long. What route does it take when it "changes direction"?

coylemj

Softshoulder wrote: »

So I know AC changes direction, but let's take one single electron changing direction in a cable 10m long. What route does it take when it "changes direction"?

It stops and goes into reverse.

alan4cult

AC is like a wave that gives energy to electrons. Don't think of it like a single electron has to pass through from one end to another, think of it more like how waves move in water, does the droplet of water move from one end to another? It doesn't but the energy still transfers.

coylemj

alan4cult wrote: »

AC is like a wave that gives energy to electrons.

The 'wave' that you're thinking of is the graphical representation of the AC voltage in a diagram where it looks like a sine curve.

Electricity is not wave energy, it involves the movement of electrons.

bob mcbob

coylemj wrote: »

The 'wave' that you're thinking of is the graphical representation of the AC voltage in a diagram where it looks like a sine curve.

Electricity is not wave energy, it involves the movement of electrons.

Technically, the electrons only move if they have an electric field applied to them. So is electricity the movement of the electrons or the electric field?

It is pretty complex - defined by Maxwell's laws. (He was a genius)

Here is the basic description

https://simple.wikipedia.org/wiki/Electricity

Bruthal

CoBo55 wrote: »

Tesla would be turning in his grave,

By AC induction?

Softshoulder

coylemj wrote: »

It stops and goes into reverse.

How far does it go until it changes direction?

2011

Softshoulder wrote: »

How far does it go until it changes direction?

That depends on a number of factors including the frequency. The frequency expressed in Hertz is an indication of how many times the current changes direction per second. The electrical current travels at the speed of light so it can be pretty far is the answer!

bob mcbob

Softshoulder wrote: »

How far does it go until it changes direction?

if you are trying to understand, look at DC first it is simpler.

Think of the copper cable as a perfectly flat boat canal - the water is moving but in no particular ordered manner.

To add a battery to this, this raises one end of the canal and gravity causes the water to roll downhill. The energy is the movement of the water but it is actually caused by gravity.

In a DC circuit - the battery creates the electric field which causes the electrons to move.

Softshoulder

2011 wrote: »

That depends on a number of factors including the frequency. The frequency expressed in Hertz is an indication of how many times the current changes direction per second. The electrical current travels at the speed of light so it can be pretty far is the answer!

So basically from the transformer, through the item being powered, along the neutral all the way back to the transformer and then ground, it changes direction?

What about if there's an LED that only allows flow one way? How does that affect the flow and change?

Softshoulder

bob mcbob wrote: »

if you are trying to understand, look at DC first it is simpler.

Think of the copper cable as a perfectly flat boat canal - the water is moving but in no particular ordered manner.

To add a battery to this, this raises one end of the canal and gravity causes the water to roll downhill. The energy is the movement of the water but it is actually caused by gravity.

In a DC circuit - the battery creates the electric field which causes the electrons to move.

I'm ok with DC I think. I have an engineering degree, not for electrical but some.

Electrons flow from one side to the other because one side is positively charged and the other is negative meaning it has more electrons than protons.

Bruthal

2011 wrote: »

That depends on a number of factors including the frequency. The frequency expressed in Hertz is an indication of how many times the current changes direction per second. The electrical current travels at the speed of light so it can be pretty far is the answer!

I have a feeling they don't move much at all.

Zubeneschamali

2011 wrote: »

The electrical current travels at the speed of light so it can be pretty far is the answer!

No, electric fields propagate at light speed, but the actual electrons move very slowly, less than a mm per second. The technical term is drift velocity if you are looking it up.

Bruthal

An analogy maybe a km long tube of marbles, 80,000 of them all in contact. Push one end an inch, one at far end 1km away will move an inch, but the response time probably the speed of sound in glass over the km. So a small movement at very low speed moves the far end almost immediately.

2011

Zubeneschamali wrote: »

No, electric fields propagate at light speed, but the actual electrons move very slowly, less than a mm per second. The technical term is drift velocity if you are looking it up.

I didn’t mention electrons, but yes I think you are correct

Bruthal

coylemj wrote: »

. Neutral completes the circuit but is otherwise passive i.e. it's the live terminal that does the work.

The neutral is as active as the phase conductor in a single phase circuit. It's just at ground potential. A closed loop is needed to do any work.

alan4cult

coylemj wrote: »

The 'wave' that you're thinking of is the graphical representation of the AC voltage in a diagram where it looks like a sine curve.

Electricity is not wave energy, it involves the movement of electrons.

The electrons do move but they do not get displaced on average. Their net position is 0, same as the water in a lake when a wave hits.
In DC the electrons cycle around the circuit.

Cerco

So are electrons particles, waves or both?

CoBo55

Bruthal wrote: »

By AC induction?

Asynchronously....

Zubeneschamali

alan4cult wrote: »

In DC the electrons cycle around the circuit.

Yes, but that doesn't mean each electron zooms around the whole circuit. It's more like water in a hose: some water goes in one end, some water comes out the other end.

You can think of voltage being like water pressure, and current being the amount of water flowing out.

alan4cult

Cerco wrote: »

So are electrons particles, waves or both?

Electrons are particles moving back and forth under AC.
Under DC they moved one way negative to positive, differing from conventional current which is labelled positive to negative.

Zubeneschamali

Electrons are not really particles or waves. Saying they behave like a wave or particle are ways for us to try and understand their behaviour.

Tiny things are weird because at that scale quantum effects are important and nothing acts the way things do at the everyday scale we see.

Cerco

Zubeneschamali wrote: »

Electrons are not really particles or waves. Saying they behave like a wave or particle are ways for us to try and understand their behaviour.

Tiny things are weird because at that scale quantum effects are important and nothing acts the way things do at the everyday scale we see.

I was expecting the field of quantum mechanics to raise it’s head sooner or later.
The presence or absence of a particle is described by probability as is the duality of wave /particle phenomenon. One intriguing part is the possibility of a particle being in two locations simultaneously.

alan4cult

Zubeneschamali wrote: »

Electrons are not really particles or waves. Saying they behave like a wave or particle are ways for us to try and understand their behaviour.

Tiny things are weird because at that scale quantum effects are important and nothing acts the way things do at the everyday scale we see.

I'm pretty sure electrons are particles, no?

CoBo55

My god there's some jargon on this thread.

alan4cult

CoBo55 wrote: »

My god there's some jargon on this thread.

The atmosphere is electric!

Softshoulder

After 30 posts there isn't a clear consensus on how AC moves back and forth in a circuit.



Should I just accept that "electricity changes direction 50 times a second in a 50Hz supply or is there a clear answer?

And if it changes so many times a second, how does that work with LEDs that allow one way flow?