# Thread: How fast is Electricity!!!

1. ## How fast is Electricity!!!

I am on the top of a mountain. 10km down in the valley I have a spot light. The electric lead is exactly 10km long, and runs to a switch that I control at the top of the mountain.

Q:
How long does it take for the light to turn on after I flip the on switch at the top of the mountain???

2. ## Re: How fast is Electricity!!!

Even though the electrons move down the wire at a few centimeters per second, the electric field will travel at the speed of light, 30,000,000,000 metres per second, or 30,000,000 Km per second. So the light should turn on after 1/3,000,000 of a second.

StuartR

3. ## Re: How fast is Electricity!!!

Is the speed of light and electricity the same?? I did not realise that!

4. ## Re: How fast is Electricity!!!

<img src=/S/whisper.gif border=0 alt=whisper width=29 height=17> Actually the speed of light is approx. 300,000 km/sec so the light will turn on after 1/30,000 of a second. What's a factor of 100 between friends? [pedant]

If you want to get relatavistic about this you will actually see the light come on another 1/30,000 second after it does!

Also I guess it depends on the type of bulb as to how long it takes to start emitting light after powering up. <img src=/S/dizzy.gif border=0 alt=dizzy width=15 height=15>

5. ## Re: How fast is Electricity!!!

Not to mention the fact the <img src=/S/lightbulb.gif border=0 alt=lightbulb width=15 height=15> light will have to travel uphill which will slow it down even more...

6. ## Re: How fast is Electricity!!!

But in South Africa it is downhill!!

7. ## Re: How fast is Electricity!!!

Very true! <img src=/S/laugh.gif border=0 alt=laugh width=15 height=15>

OK - but then the electrons will have to go uphill! Or do they start at the bottom of the hill, go up to the switch and then back down again?

8. ## Re: How fast is Electricity!!!

<img src=/S/dizzy.gif border=0 alt=dizzy width=15 height=15>.....you guys....you are amazing..... <img src=/S/laugh.gif border=0 alt=laugh width=15 height=15>

9. ## Re: How fast is Electricity!!!

[hem] [hem]

Deputy Assistant to the Under Secretary to the Acting Lounge Pedant (Geology Division) here

In SA they neither have an up hill or a down hill, they only have flat hills as the following image depicts.

10. ## Re: How fast is Electricity!!!

And I suppose you have proved this with another of your Kitchen Table Mountain experiments?

11. ## Re: How fast is Electricity!!!

Excellent, a cracking Rudi question...Now from my recent experimentation in the Kitchen I have calculated the following:

It is said that electric current, which flows in a conductor, conducts electricity. Also in an electric wire free electron flowing
in a conductor creates electric current.

As for free electrons inside a conductor, the most common material for a conductor of electric wires is copper and the
electron density in 1m^3 is 8.5e28. For example in copper wire, of which length is 1m and the outside diameter is 0.5mm,
there are 1.7e22 free electrons, which is enormous. Since copper is one monovalence metal, the number of free electrons
and copper ions (atom) are the same.

By the way, free electrons in a copper wire move to random directions with the speed of 1.3e6m/s even in the case of no
electric current, which means it is not in electric field. This velocity is called "Fermi velocity" and it exists even under 0
absolute temperature. It is not heat energy and originated from indefinite theory of quantum mechanics. Since electric
current is average flow of free electrons, in other word "drift velocity", electric current doesn't exist under this circumstance.

When voltage is put on both sides of a conductor, free electrons increase the speed in proportion to the electric field and by
lattice oscillation, lattice defect, and collision with impurities, they will be scattered to different directions from the electric field
and lose the speed to the direction of the electric field. Therefore it doesn't increase the speed infinitely and it will keep certain
average velocity. That means collision functions as a kind of friction.

As for copper, the time interval between collisions is 5.26e-45 seconds and average drift velocity is, 4.62e-3 (m/s) / (v/m).

It means that when 1V voltage is put on both ends of 1m long copper wire, the velocity of free electrons to length direction
is 4.62 mm/s. It seems amazingly slow but since electric charge of electrons is -1.6e-19c, 12.6A electric current flows in the
0.5mm copper wire with this speed.

12. ## Re: How fast is Electricity!!!

I have absolutely no idea where those extra zeros could have come from. I've looked all round the house and there aren't any missing from anywhere else. Maybe they're Lex's and they wanted to have a look at some loungers today.

StuartR

13. ## Re: How fast is Electricity!!!

Can I seek clarity Mr Rudi

Do the wires that connect the light bulb and the switch covered in plastic or are they bare as this will affect the calculation. If the wires are bare then Steve and Stuart's answers will be correct but covered wires will have a slower "speed" due to the geometry of the plastic and the permittivity of the material....neeed ....mooooore...iiiiinnnnfooooormatiooon........

14. ## Re: How fast is Electricity!!!

The wire is intermitent....500 meters are covered in plastic and the next 500 meters are bare....at a certain area about 4km in, the wire runs through a flooded river where it is half bare (or should that be bear!!) and half plastic. Oh...and the ground at the foot of the mountain also has an unusually high magnetic factor as the mountains have a high iron ore density!!!

Does with help for your calculations?????????

15. ## Re: How fast is Electricity!!!

Ahh yes, thanks for that clarification, <img src=/S/hmmn.gif border=0 alt=hmmn width=15 height=15>iron ore density, thought that may be the case, that will affect my calculations as I was expecting malachite deposits...back in a moment

<img src=/S/whisper.gif border=0 alt=whisper width=29 height=17>That bloke always changes his mind....mumble, moan,....up hill, down hill, in the maids chamber, magnets, light..mumble...now electricity, has the world gone mad.......

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