# Bird on a wire

Discussion in 'Physics' started by activee, Apr 15, 2014.

1. ### activee Thread Starter Member

Jan 16, 2014
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Hey I'm reading the first chapter on this website and it says a bird which stands on a circuit isn't hazardous because there is no difference of potential between two points. But to me there is a difference of potential between the bird's body and the wire. I mean the excess of electron in the wire should balance and go into the bird.
I understand why a person standing in the ground will be shocked.

Also hypothetically : if the current in the wire of a circuit is high enough could the bird be shocked due to the air around him being ionized and thus no more insulating ? So the air will be like the earth when a person touches an electric wire.

Thanks

Oct 18, 2012
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3. ### MrChips Moderator

Oct 2, 2009
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As the bird approaches the wire before it lands on the wire the bird is in an electric field.
There will be a potential difference and a separation of charge between the bird's feet and its head.

As the feet touch the wire there will be an infinitesimally small flow of charge exchanged between the bird and the wire. The bird will not feel a thing.

Air around the wire is a poor conductor. No current flows from the wire to the air.
It doesn't matter how much current is flowing in the wire.

4. ### R!f@@ AAC Fanatic!

Apr 2, 2009
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And I thought of the film, Bird on a wire. Sheeesh.!

5. ### activee Thread Starter Member

Jan 16, 2014
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Thanks. Some people in your link seem to say the current doesn't pass through the bird.
If I connect a wire only to the negative end of a battery. According to static electricity it will get negatively charged right ?
like this
It's basically the same with the bird. The bird is neutral before it lands but the wire isn't so it should get electrically charged..

Do you mean that as the bird enter the electric field it gets gradually charged ? Is it possible then that the bird enters it at a speed so fast that the result would be an electric shock ?

Last edited: Apr 15, 2014
6. ### tshuck Well-Known Member

Oct 18, 2012
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When people say there is no current, they mean that there is no substantial current. If you want to talk about such small currents, you'll need to take into account the neurons in the bird and the muscle contractions. There comes a point where we say there is no current because we are approaching the subject from a broader perspective, where femtoamps are much smaller than any other currents we are talking about - namely, that of the wire - and are negligible in comparison. The bird would not be harmed by such small currents (otherwise, simply lifting a wing would mean being shocked).

7. ### MrChips Moderator

Oct 2, 2009
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As the bird approaches the electric field, the bird does not become charged.
Electrons will drift across the bird so as to balance out the electric field.
The speed of the bird has little effect unless it was travelling close to the speed of light.

When the bird touches the wire it becomes charged (assuming that the wire is at a DC voltage).
If the voltage on the wire is alternating, there is no net charge on the bird.

8. ### MrChips Moderator

Oct 2, 2009
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Your picture with the battery and wire is not exactly correct.

What happens if the wire touches the +ve terminal of the battery?
Does it become positively charged? I don't think so.

Similarly, it is not correct to say that the wire becomes negatively charged if it touches the -ve terminal of the battery.

9. ### THE_RB AAC Fanatic!

Feb 11, 2008
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Wires are usually insulated.

10. ### R!f@@ AAC Fanatic!

Apr 2, 2009
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I think Chips need to see insulated drawing.

11. ### activee Thread Starter Member

Jan 16, 2014
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Well if I have one negative object and one neutral object and if both touch each other they both get negatively charged. I don't think I got this wrong :s. Assuming they are conductors.
And yeah I think if the wire touches the + terminal it becomes positive since some electrons will leave the wire to balance the problem.

Last edited: Apr 15, 2014
12. ### MrChips Moderator

Oct 2, 2009
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Well I think you have that wrong.

Suppose you have a 9V battery.

What is the potential at the +ve terminal?
What is the potential at the -ve terminal?

13. ### activee Thread Starter Member

Jan 16, 2014
39
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I know what you are trying to make me say but that's not really what I'm talking about

The + terminal has a deficiency of electron while the - terminal has a surplus of electron. The difference of potential between the + and - terminal is 9v. There is no potential energy of the + terminal if not compared to another point, same goes for the - terminal.

I already know that. I'm talking about static electricity. If an object A is negatively charged and object B is neutral it is in my understandings that if both touch each other the result will be that both will be negatively charged since the surplus of electrons in object A will balance and go in object B thus both being ionized. Like the glass rod and silk.

This can't possibly be wrong, right ?

Now if that object A is the - terminal and object B is a bird the bird should be ionized. If it's ionized it means electrons are travelling to it. Electron travelling equals current thus there is a current.

14. ### MrChips Moderator

Oct 2, 2009
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Ok, I give up. If you know all the answers why bother to ask.

15. ### Metalmann Active Member

Dec 8, 2012
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I've seen several birds land on old, uninsulated , wires; and they seem to leave just fine.

16. ### R!f@@ AAC Fanatic!

Apr 2, 2009
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Does OP understand the Potential difference ?

He should not get close to house hold main terminals cause he will be charged and will get a shock.

17. ### activee Thread Starter Member

Jan 16, 2014
39
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I'm telling you my understandings as is right now of the things. You are just telling me no it doesn't work like that.

Maybe you can point out where I'm wrong ? That should be something more constructive.

<< If a conductive wire is placed between the charged wax and wool, electrons will flow through it, as some of the excess electrons in the wax rush through the wire to get back to the wool, filling the deficiency of electrons there >>
This is what I'm saying.

It's the electrical pressure. How willing the electrons are to go from point A to point B. 1 volt is the release of 1 joule by one coulomb of charge.

Last edited: Apr 16, 2014
18. ### R!f@@ AAC Fanatic!

Apr 2, 2009
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It just does not work like tht.

19. ### activee Thread Starter Member

Jan 16, 2014
39
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It's written on this website.

<< If a conductive wire is placed between the charged wax and wool, electrons will flow through it, as some of the excess electrons in the wax rush through the wire to get back to the wool, filling the deficiency of electrons there >>

I'm just switching the Wax by a ev- terminal and the wool by a wire. If that's not possible then why?

20. ### MrChips Moderator

Oct 2, 2009
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You don't see electrocuted birds falling from a 500,000V transmission line.

Ok, here is a physics experiment you can work through.

Take a metallic sphere, 1m in radius, insulated and supported 1m off the ground, i.e. the center of the sphere is 2m from the ground.

Connect a 12VDC battery, +ve terminal to the sphere, -ve terminal to ground. The sphere is now charged to +12V.

Take a second identical sphere but this time reverse the polarity of the 12VDC battery, i.e. -ve terminal to sphere, +ve terminal to ground. The second sphere is now charged to -12V.

Remove the 12V battery.

There is 24V potential difference between the two spheres.

Now connect a 1Ω resistor between the two spheres. Current flows through the resistor and the potential between the two spheres is reduced to zero.

Calculate the current flowing through the 1Ω resistor.