Current question.

[cross]

Hey everyone,

Quick question.

Is it possible for there to be voltage in a wire but no current?

Im asking mainly in regards to the live wire running to a powerpoint. If you were to measure the amps of this wire using one of those clamp type multimeters with nothing plugged into the point would there be any current flowing through the wire or would it just not give you a reading because the circuit is open?

thanks alot.

 

[Damocles]

Hi double, red, or St George's.

Your question is difficult to answer because it contains implied contradictions.

If you clamped the live wire only it would probably show no current flowing either because there was nothing plugged into the point or because the circuit was open. It would probably read 0.

On the other hand, if the meter was sensitive enough it would show a leakage current on the microamp level.

On the large scale it is possible to have voltage without current. On the microscopic level current is electrons moving and voltage is a pile-up of electrons in one place. So it is impossible to create a voltage without moving electrons about. There always has to be some current.

 

[plugwash]

voltage is presure current is movement

you can have a pipe at an insanely high preasure but if you cap the end then nothing will flow out of it

however to measure voltage some current has to flow through the meter (though the amount is very tiny)

 

[cross]

Thanks for your replies,

I was just wondering because when you plug something in the current increases to the appropriate amount depending on the wattage of the equipment doesnt it? Its not like if its a 20amp circuit there is constantly 20 amps running through the cables.

 

[notb665]

On the microscopic level current is electrons moving.

You must have a good microscope!

 

[Damocles]

Yes, an electron microscope.

Think of electricity like a very big and hungry lion in the corner of you living room. Fortunately he is wearing a collar. If that breaks, there is a rope round his foot. If he chews through it, he is in a cage. If he rips the cage apart, there is a big axe held up by a rope over his head....

Electricity is a bit like that. Lots of handy tricks to make sure it stays nice and safe. Caged lion waiting to pump current.

20A circuit has a big axe suspended over the cable ready to swing if the current goes above 20A. Normally it is caged, so nothing. Then plug in something and you let a bit out. But it doesn't increase to an appropriate amount. It is sitting there kicking and screaming and scheming to get free.

 

[notb665]

But you can't see electrons in an electron microscope!

 

[Damocles]

You can't see anything EXCEPT electrons in an electron microscope

 

[notb665]

No, honestly, you can't see electrons in an microscope. What I used to see every day at work and in the three years I spent studying electrons, is how the sample affects the electron beam.

Electrons move far too fast to see them, that's why you can only see what they do. It is also for this reason that they, and their fields, are actually theoretical entities, overwhelming though the evidence may be.

Plus an electron microscope would take up an entire, large room!

 

[dingbat]

Yes, an electron microscope.

Think of electricity like a very big and hungry lion in the corner of you living room. Fortunately he is wearing a collar. If that breaks, there is a rope round his foot. If he chews through it, he is in a cage. If he rips the cage apart, there is a big axe held up by a rope over his head....

Electricity is a bit like that. Lots of handy tricks to make sure it stays nice and safe. Caged lion waiting to pump current.

20A circuit has a big axe suspended over the cable ready to swing if the current goes above 20A. Normally it is caged, so nothing. Then plug in something and you let a bit out. But it doesn't increase to an appropriate amount. It is sitting there kicking and screaming and scheming to get free.

Bloo*y hell, I'm not coming round your house!!!

 

[ban-all-sheds]

Its not like if its a 20amp circuit there is constantly 20 amps running through the cables.

No - a "20A circuit" means one which has the capacity to safely carry 20A.

 

[ban-all-sheds]

Bloo*y hell, I'm not coming round your house!!!

I am.

Provided I can have some of what he's been smoking...

 

[dingbat]

I just had a startling vision of FWL_Jim, Damocles, B-a-S and a bloomin' great lion... all handing round a joint and discussing the merits of DIY electrics. I won't sleep for weeks!