A basic electrics question.

[ClichéGuevara]

Very slow, in a wire - you'd be surprised - of order a mm a second or less. Think ping pong balls in a pipe. Push one at one end and the one at the other end moves almost instantaneously- but any individual ball moves hardly at all.

You've obviously seen my trying to play ping pong.

 

[Wobblers]

[QUOTE 4991505, member: 9609"]so how quick does an appliance start up after the switch is turned on - lets say one mile of cable, and does voltage matter ?
is it the speed of light ?[/QUOTE]

It's the electric field that gets all those electrons moving (albeit slowly), and it travels at the speed of light. Voltage, or more correctly the potential difference along the wire, only determines the strength of the electric field, not the speed at which it travels.

AC is a little different, as the voltage at any one spot is always changing.. That means the electrons don't actually move, but merely vibrate about one position. You might be wondering how energy gets down the wire if the electrons aren't moving! Put simply, the energy is carried by the electric field: one way of looking at it is to visualise waves of enormously long wavelength travelling down the wires.

 

[Wobblers]

[QUOTE 4991534, member: 9609"]I understood your first paragraph, second one was getting a bit deep[/QUOTE]

The TL;DR version is that electrical energy is carried by the electric field. With DC, that field always points in one direction, with AC it changes direction at regular intervals.

 

[lazybloke]

Many appliances haven't had a physical/mechanical power switch for years. Power consumption in standby used to be a big problem.

 

[swansonj]

The TL;DR version is that electrical energy is carried by the electric field. With DC, that field always points in one direction, with AC it changes direction at regular intervals.

Umm. One hates to quibble. But don't you think that the energy is actually carried, not by the electric field alone, but by Poynting's Vector, which is the vector cross product of the electric and magnetic fields? So when the electric field reverses direction each half cycle of an AC waveform, so does the magnetic field, and hence the energy flow remains in the same direction?

[/one physicist talking to another mode]

 

[Fab Foodie]

Electrons travel at the speed of light as any fule kno. As soon as you push the switch the light comes on....
Don't make it any more complicated than that please....

 

[subaqua]

Electrons travel at the speed of light as any fule kno. As soon as you push the switch the light comes on....
Don't make it any more complicated than that please....

There's some senior electrical engineers that only have that understanding ......

 

[Tim Hall]

Just make sure there's a plug in an otherwise empty socket, or the electricity will leak out all over the floor.

 

[ClichéGuevara]

Electrons travel at the speed of light as any fule kno. As soon as you push the switch the light comes on....
Don't make it any more complicated than that please....

I thought the switch turned the dark off.

 

[Fnaar]

Miss Goodbody's appliances leap into action whenever she flicks the button.

 

[cosmicbike]

Miss Goodbody's appliances leap into action whenever she flicks the button.

I'm sure she knows how to turn you on too....

 

[subaqua]

Miss Goodbody's appliances leap into action whenever she flicks the button.

is that the buttonbean I hear people talking about ? Cos she mentioned something about beans and flicking the other day

 

[marinyork]

Umm. One hates to quibble. But don't you think that the energy is actually carried, not by the electric field alone, but by Poynting's Vector, which is the vector cross product of the electric and magnetic fields? So when the electric field reverses direction each half cycle of an AC waveform, so does the magnetic field, and hence the energy flow remains in the same direction?

[/one physicist talking to another mode]

The Poynting vector is just a representation useful to us i.e. (directional) energy flux. The field(s) is very much the more profound quantity and deeper insight. Although the Poynting's Theorem is a profound insight, leading to an appreciation of a local conservation of energy. The actual Poynting Vector is more 'useful' imho for things like NIMs. Poynting's Theorem follows from deeper symmetries though - the conservation of the stress-energy tensor.

 

[marinyork]

Electrons travel at the speed of light as any fule kno. As soon as you push the switch the light comes on....
Don't make it any more complicated than that please....

The problem is that GCSE Physics actually tells you a lot of 'useful' stuff. Such as refractive index and dispersion, all the optics stuff in general and total internal reflection. What teachers don't tell people is the subtle bits like group speed and phase speed, evanescent waves, cut outs and so on.

 

[subaqua]

The Poynting vector is just a representation useful to us i.e. (directional) energy flux. The field(s) is very much the more profound quantity and deeper insight. Although the Poynting's Theorem is a profound insight, leading to an appreciation of a local conservation of energy. The actual Poynting Vector is more 'useful' imho for things like NIMs. Poynting's Theorem follows from deeper symmetries though - the conservation of the stress-energy tensor.

My pointing theory is at shiny things and strange objects and going oooooh .