basics of static electricity

[paul]

i've been trying out the beginners experiment of rubbing a comb through my hair, then using the charged comb to bend a small trickle of water from a tap.

 

a) does the comb strip electrons from my hair? or vice versa?

 

b) why does the water bend?

[iNow]

The comb does pull electrons from your hair, causing the comb to be negatively charged. Then, when you place the comb near the water, it bends for the same reason that magnets attract and repel one another.

 

Now, can you repeat back in your own words the answers to the questions you asked?

 

Also, if the comb pulls electrons from your hair, what happens to the electric charge in your hair after you've combed it and removed those electrons?

 

 

EDIT: Also, Paul, what is it about the structure of water (what it's made of) that causes it to bend in response to the presence of a comb packed with extra electrons?

Edited November 28, 2008 by iNow

[paul]

thanks iNow, i'll try to explain what i've learned so far;

 

the comb strips electrons from the hair, making the comb negatively charged. the water molecules are made of H and O atoms. the H atoms have a slight positive charge, the O atoms a slight negative one. the H end of the water molecule is therefore attracted to the negatively charged comb.

 

and the hair strands that are left positively charged (having been stripped of electrons) now stand on end because they're repelling each other (like charge repels like).

 

is that right?

[iNow]

Very well done, sir. I do believe you've got it.

[paul]

thanks again iNow, but i've been learning more and i'm now not so sure about the reason i gave for the water being attracted to the charged comb;

 

i've now been told that the charged comb picks up neutral objects. what happens is, the electrons of the atoms of the neutral surface (eg, small bits of paper) are repelled by the charged comb. they move away, but only so far (as paper is an insulator). this leaves the positively charged protons of the paper atoms susceptible to the charged comb, and they're attracted.

 

is that right?

 

if so, is that what is happening with the water also? or with the water is it really due to its polarity (unlike the bits of paper)?

[iNow]

Well, the water is neutral also. AFAIK, the negatively charged comb essentially "pushes" the negative charges in the other material as far away as possible. So, with your example of the paper, the negative charges essentially "run" from the comb. It's being polarized. This can cause the paper to move, much like the bending water.

 

It's just simple electromagnetism.

 

If you want more detailed explanations, then you're going to be beyond my personal education and ability to teach. You might check out something like this:

 

http://www.physics.sjsu.edu/becker/physics51/elec_charge.htm

 

 

Otherwise, there are members at this site very much better versed in the dynamics of electromagnetism than me, and perhaps they'd be willing to step in and help. Enjoy.

 

 

 

 

Although the charges (on the electrons) are tightly bound to the atoms in an insulator they are free to move slightly within the atom. This is called

polarization

. If a plastic comb is rubbed on fur (or your dry hair) electrons will be rubbed off the hair onto the plastic comb. The plastic comb becomes charged negatively. If the comb is brought close to a neutral insulator, like a piece of dry paper, it will repel the negatively charged electrons in the atoms causing them to moving away slightly, leaving the protons without an electron closer to the comb. Since opposite charges attract and the positive charges are closer to the comb than the negative charges, the piece of paper is attracted to the comb. This effect is used to remove soot and ashes from smoke going up industrial chimneys. The inventor became rich as a result of his patent!

 

Part (b) of the diagram shows the same result (attraction of the paper) even if we had a positively charged comb.

[YT2095]

it bends for the same reason that magnets attract and repel one another.

 

It's just simple electromagnetism.

 

there are members at this site very much better versed in the dynamics of electromagnetism than me

 

indeed there are, and it`s got NOTHING at all to do with magnetism, electro or otherwise!

[Gilded]

indeed there are, and it`s got NOTHING at all to do with magnetism, electro or otherwise!

 

They are very much linked. It's called the electromagnetic force for a reason.

[YT2095]

electroMOTIVE force, not magnetic, http://en.wikipedia.org/wiki/Electromotive_force

elcrostatic: http://en.wikipedia.org/wiki/Electrostatic

[iNow]

Okay, I welcome correction, and appreciate the links. Can you help me to better understand the basic difference between electromagnetism as I suggested in polarizing the objects and electrostatics or electromotive forces causing the bend in water and the paper to move in response to the comb?

 

I'm not sure what I said was wrong, but welcome an quick tutorial on why these other terms apply better.

[YT2095]

simply put, electromagnetics has an electrical and magnetic component to it.

 

this phenomenon (bending of water) is entirely an electrical response with no magnetics/magnetism involved.

it`s basic electrostatics here: http://en.wikipedia.org/wiki/Electrostatics

the link answers the guys question nicely.

[iNow]

So, it's more about induction of charge? What I suppose I'm missing is, if the surface of the object is charged, and hence later repelled or attracted as a result of that charge, what causes the repulsion/attraction if not magnetism?

[YT2095]

your missing the "Strong Nuclear Force", it`s one of the 4 nuclear forces.

Electromagnetic force is one of the other remaining 3, Gravity and Weak nuclear force being the other 2.

they`re all really inter-related and inescapable (even in this) but it`s senseless to overcomplicate things.

Edited November 29, 2008 by YT2095

[iNow]

That's fair, but if it's the strong nuclear force, then why do the objects need to be polarized/charged to exhibit this behavior? Why would polarization be relevant in terms of the strong interaction? I would think that if the reaction were a result of the strong force, then this reaction would be independent of charge and polarity. It's probably painfully obvious to you, but I'm not seeing it.

[YT2095]

ok, this is going to be a whole easier to Rewind and start from the beginning again for clarity`s sake.

 

the comb/water effect is induced by triboelectrics.

here: http://en.wikipedia.org/wiki/Triboelectric_effect

 

this in turn creates an electrical potential.

here: http://en.wikipedia.org/wiki/Electrostatic_potential

which in turn has an electric field, here: http://en.wikipedia.org/wiki/Electric_field

 

in specific related to electrostatics here: http://en.wikipedia.org/wiki/Electric_field#Properties_.28in_electrostatics.29

 

the electrons (electrical field) exerts a pressure, and that causes movement.

[Klaynos]

Any interaction that involves charge, is an electromagnetic force. It is done by the exchange of photons, whether you're talking about electrostatics or electrodynamics, it's electromagnetism. They are unified forces.

 

That includes the electromotive force, or triboelectrics...

 

The other 3 fundamental forces are negligible in this case.

[YT2095]

and Where in the EM spectrum does it fit then? what frequency is it?

[Klaynos]

They're virtual photons, IIRC you cannot easily say they are of a certain frequency, or even if you can give them one at all as their frequency would be related to the distance (and therefore time of existance).

 

Unification of electricity and magnetism is one of science greatest achievements imo, it was the first relativistic theory (even if this wasn't fully appreciated at the time), Maxwell's equations clearly show that they are the same thing.

[swansont]

I think the the confusion here is that "electromagnetic force" conjures the image of an electro-magnet, and there is no magnetic interaction in this case.

 

It is perfectly fine to call it the electromagnetic force; as Klaynos has stated, it's in Maxwell's equations — the two forces are trivially unified. A purely electrostatic effect (such as this) will have a magnetic component in another frame of reference, where the charge on the comb will be in motion.