Re: [Phys-l] Q from amplitude width?

[brian whatcott <betwys1@sbcglobal.net>]

On 4/25/2011 10:56 AM, Bernard Cleyet wrote:
> On 2011, Apr 25, , at 04:41, brian whatcott wrote:
>
> > It is not conservative to suppose that input power to a solenoid is
> > proportional to the square of  input voltage amplitude, where the drive
> > voltage varies in frequency.
> >
> > Brian W
>
> I thought about that, i.e. Z(L)  =  i *2Pi* f* L
>
>
> The L measured at 100 Hz is ~0.2 H
>
> This is an air core coil;  with the complete core, it rises to ~ 12 H!   [It's a disassembled low power filter choke.]
>
> The frequencies are ~ 5.5 R,  so ~ one ohm added in quadrature to the resistance (ohmic) ~390 ohm.
>
> Conclusion: objection denied.
>
> Furthermore, if the R were zero, the current would vary only ~  10% in the most extreme case.   That's about the same as my amplitude resolution!
>
> bc  thought to include a current meter, but decided unnecessary.   n.b., the EMFs NOT measured with a digital meter!
It is more conservative to establish what the resonances are in the 
drive coil, rather than model
it as an L and R in series, but better to check the drive current too.

Not sure what frequencies are given as ~5.5 R, so let me ask directly: 
what is the resonant frequency of the mechanical pendulum that you are 
using?

Brian W