Re: [Phys-l] entropy and electric motors

[Bernard Cleyet <bernardcleyet@redshift.com>]

> could also reach a Q > 1000 with considerable design effort).


Misquoted or bc typo.

synchronome free decay Q ~ 10k .

It is given a v. slight "push" every 30" (60"?) by a weight dropping  
on the rod's arm.  Another? arm steps a counting wheel.  A simple  
rotary motion sensor (old model) used as the suspension of a simple  
pendulum (rod v.~ .6 m; bob mass, 0.15k g) achieves at max. Q ~1k .

Of course this is artificial, as the escapements decrease the Q.

> The tuned circuit is distinguished by the capability of processing
> exciting signals
>   smaller than the amplitude of the ambient thermal electrical  
> noise in fact.

The narrower the band width the longer the time constant in synch.  
detectors -- but the sig. is correspondingly detectable "deeper into  
the noise".   A tuned circuit is indeed similar.   Incidentally radio  
detection may use mechanical filters (quartz crystals) if the signal  
is also narrow, e.g  morse code




On 2008, May 27, , at 10:11, Brian Whatcott wrote:

> At 03:45 PM 5/22/2008,  Kyle, you wrote:
>
> > Does anyone know (or can point me to an explanation) of how the  
> > 2nd law
> > applies to electric motors and generators?
> >
> > I think I understand how the 2nd law applies to heat engines and I  
> > have
> > an elementary understanding of entropy as it relates to chemical
> > reactions. These applications explain why heat engines and fuel cell
> > efficiencies cannot be 100%. I assume the 2nd law applies somehow to
> > motors and generators but how do you find the theoretical limit for
> > them? (I know this is quite high since electric motors with 95%
> > efficiency are already available.)
> >
> > kyle
>
>
> When I stood in the steam engine hall of the Science Museum a week  
> or two ago,
> admiring James Watt's efforts, it was salutary that his great  
> improvements
> in thermal efficiency resulted in monsters of several tons weight  
> providing
> a few HP.
> This energy conversion is in stark contrast to the energy transfers  
> involved
>   in a tuned circuit which can provide quality factors in the  
> thousands
>   (you will also recall that the timing elements of clocks to which
> bc recently alluded
> could also reach a Q > 1000 with considerable design effort).
>
> The electric motor is somewhat comparable to the tuned circuit, in
> that the motor too
> is in the business of converting electrical to magnetic forces.  Like
> the tuned circuit
> and the pendulum, the motor can have very small limiting losses  - in
> this case,
> the bearings and the air drag involved.
>   The tuned circuit is distinguished by the capability of processing
> exciting signals
>   smaller than the amplitude of the ambient thermal electrical  
> noise in fact.
>
>
> Brian Whatcott    Altus OK    Eureka!
>
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