# Homework Help: Need help for Young Physicists Tournament. Thermodynamic and I supect Electromagnetic

1. Aug 4, 2008

### Cgall24

Hey guys. This is a first post so please give me tips on how to make it better.
Anyway, the problem that I am doing stated by the International Young Physicists Tournament is:

Electro-oscillator
A mass is hung from the middle of a horizontal wire. When a current is passed through the wire, the mass may start to oscillate. Describe and explain this phenomenon.

I have researched all over the net and consulted everyone that I know and we have done the experiment and found that it does actually oscillate quite considerably.
Our testing rig is two retort stands about 1.4m away from each other, strung up between them is a hair-width copper wire with a thin plastic coating. We then hung a small copper weight (15g) in the middle. We then attached the two ends of the copper wire to a 6v AC power box via alligator clips and let the weight stop swing.
When we then turned it on and it sagged about 1.5cm and started to oscillate up and down about 2mm.

I have chased every avenue of information but unfortunately, I am stuck for a theory.

We actually have a couple ideas but with no high end knowledge of the theorem behind them we can't explain them to great enough detail.

Equations to support the idea is not necessary as the review process is more like a debate were we are pitted against other year 11 students.

I also hate complex equations!:surprised

One of our ideas that we have came up with is that because AC current in Australia is around about 50Hz, the wire is heating up and cooling down at 50Hz allowing the wire to shift the weight in the centre up and down and then the momentum of the weight and the wire create a noticeable oscillation of both weight and wire. Once again, we have NO access to anyone who specialises in any of the resulting fields.

Another idea is that magnetism is involved in some way, due to the right hand coil of magnetism. We think that the wire may be drawn into a spiral pattern by its own magnetic field causing it to want to rotate. Because of gravity, it will happily travel down but become tensioned and spring back up and then it is drawn out again and the process repeats.

Any help, ANY AT ALL! Any ideas or websites that may help and please use plain English as I'm only just starting secondary physics and I wouldn't have expected this until Universty so yeah.

Callum G

I will post a picture of the rig and possibly a rig showing the phemonena.

Last edited by a moderator: Aug 4, 2008
2. Aug 6, 2008

Re: Need help for Young Physicists Tournament. Thermodynamic and I supect Electromagn

I would put my money on magnetism. Two parallel wires with currents going the opposite direction will repel each other. However, with AC current, the currents would be going up and down meaning that this force would also be increasing and decreasing causing the oscillations. Some things that make me wonder if this is correct is whether the force would be large enough. How large of currents are you getting in the wires? Posting a picture of the rig would help. What constitutes an expert in the field by the way?

3. Aug 10, 2008

### Cgall24

Re: Need help for Young Physicists Tournament. Thermodynamic and I supect Electromagn

Hey thanks! I'll have a look into it.
Unfortunately I can't get a hold of a camera so I may be a while.
And I hae NO idea what an expert in the field would be. I would assume a phycisist specialising in magnetism.

Thanks anyway!

4. Aug 10, 2008

### Cgall24

Re: Need help for Young Physicists Tournament. Thermodynamic and I supect Electromagn

BTW:
My friend would like to know why you are called Badphysicist?
Is it an ironic name or is there more??? :P

5. Nov 15, 2008

### physisT

Re: Need help for Young Physicists Tournament. Thermodynamic and I supect Electromagn

Hey,
I'm here new too. And I don't know how to write notes.
I read your message and got intrested in it, so I started working on it. I have some guesses about the theory part but I still haven't seen the phenomenon. I did it exactly like you wrote, but it didn't move!!! Are you sure of your mesurements?! And how does your cable look?! What is the radius of it?!

6. Feb 2, 2009

### emporia

Re: Need help for Young Physicists Tournament. Thermodynamic and I supect Electromagn

It may not have worked as the Hz (presumably 50Hz) may have caused the oscillations to occur too quickly for it to be wasily visible.
May I suggest trying it with a lower Hz, it you have the equiptment to do so?

7. Feb 2, 2009

Re: Need help for Young Physicists Tournament. Thermodynamic and I supect Electromagn

1.In terms of electrical heating the the wire should alternately heat and cool as the current changes this giving rise to alternate expansions and contractions.I think,however, the effect will be small because of the thermal inertia of the wire ie the rate at which its temperature expansion etc changes this rate being reduced by the plastic coating which acts as a thermal insulator as well as an electrical insulator.
2.like badphysicist I think it is more to do with magnetism and you are seeing a demonstration of the motor effect.As the current reverses the force on the wire reverses also so with an ac supply the wire should vibrate at the same frequency as the supply.The earths magnetic field should produce an effect but a very weak one due to the weakness of the field.Try bringing a magnet close to the wire.
To help with your research try googling the following
1.Hot wire ammeter.
2.Electric motor effect and Flemings left hand rule.
3.Vibrations in strings.
I would most definately try emporias idea.Try different frequencies.

Last edited: Feb 2, 2009
8. Feb 2, 2009

### brasidas

Re: Need help for Young Physicists Tournament. Thermodynamic and I supect Electromagn

There is no written (= explicit) description of mass. My point is, did you try non-magnetic mass, and still ended up with the oscillation? If anything, any metal contains some magnetic moment, and if non-magnetic material still oscillates (which I think is the case, by the way) then how would we justify the magnetic field working there?