# Alternating current+Oscillation

1. Oct 26, 2009

### blost

Hi, It's my first poste here.

2 metal, thin, bars (length=l, mass=m) are hung on same height (distance between bars-d)
Lower end of bars are conected by metal spring (mass=0, k-spring constant, d-length)
Upper end of bars are connected with alternating current source (f-frequency).
For what f there will be strong, with ascending amplitude, oscillation. Root mean square is I.

I will be really gratefull for any seggestions.

2. Oct 26, 2009

### Bob S

Where's the force? What is causing it? The best way for electricity to produce a force is by using electric currents in coils.
Bob S.

3. Oct 26, 2009

### blost

so You mean that there will be a force betwen each of roll ? First i thing that the main force will be come from the bars... You know...F~I^2/d * l...
Could You say something more ?

But still I don't know how to conect a force and frequency...
maybe f will be conected with period of oscillation of compound pendulum ??

4. Oct 28, 2009

### blost

Bob, I will be grateful if You could say something more...

My main problem is How the force is conected with frequency.

5. Oct 28, 2009

### Fightfish

The magnetic force between the two bars is dependent on the magnitudes of the currents flowing in the two bars, that's a fact that you er..somewhat established up there right? Take note, at this point, that the current is alternating - periodically varying over time with a certain frequency f. Thus, the force between the two bars also changes with time in manner related to the frequency f of the source.

6. Nov 4, 2009

### blost

Ok. I know why the bars are oscillating, but my main problem is how. The frequency of force is 2xf, isn't it ? and now... there is problem with resonance... I must calculate a resonance frequency of coils or bars ?
The mas of cails =0 so i suppose that a normal mode of an oscillating -->0.