24 fps, blue ray and my telly.

In article , Bill Wright
writes

"Peter Duncanson" wrote in message
.. .
On Sun, 07 Sep 2008 22:30:45 +0100, Andy Burns
wrote:

On 07/09/2008 22:23, Bill Wright wrote:

Why does the supply frequency vary with load?

What happens to your van if you approach a hill and don't push the loud
pedal hard enough?

An even closer analogy is belting along on the level in the van
with the loud pedal as far down as possible and then meeting a
hill. If the hill is up, the van will go slower - lower
frequency of rotation of the wheels. If the hill is down, the
van will go faster - higher frequency of rotation of the wheels.

All this is obvious. But are you saying that the speed of all the turbines
is governed by simple mechanical load? I assumed things would be more
sophisticated. How are the turbines synced?

Its not mechanical load as such, but electrical load. Same thing
happens with a petrol generator when you exceed its capacity - it slows
down, struggling to keep the voltage up but going so at a lower
frequency.

I was aware that the mains behaved in this way long before I heard of
dynamic demand. About 25 years ago an astronomer colleague of mine
built his own telescope (ground the 10" mirror himself!) and wanted an
electronic drive for it. He designed a motor gearing system that
required a 50Hz drive to match the earth rotation and I designed a drive
circuit and the 50Hz +/- ?Hz supply so that he could synch up to various
astronomical objects (eg. sidereal time, lunar time, planets etc.). I
recall it had two digital LED displays - the first was the required rate
that he could dial in based on his astronomical charts or half a dozen
defaults like sidereal rate, and the second was the error - which was
important for taking long exposure photos.

During the build, I tested the feedback (the error rate) using a demand
rate of 50Hz against the mains rate, and was quite surprised how much it
slowed down at 9pm. I now realise it was millions of kettles being
switched on just as the programme before the BBC News finished!

Design, telescope and colleague have long since passed.
--
Kennedy
Yes, Socrates himself is particularly missed;
A lovely little thinker, but a bugger when he's ****ed.
Python Philosophers (replace 'nospam' with 'kennedym' when replying)

"Andy Burns" wrote in message
et...
Higher frequency waves of same amplitude have higher energy don't they?

Dunno. It takes more watts to make bass loud compared to treble.

Bill

In article , Bill Wright wrote:
I do know that when I was at college (in the sticks) our gramphones used to
have to be set at 78 to play 45s during January. As you will gather none of
us had perfect pitch.

Wasn't that just to make those awful records you'd been given for Christmas
finish sooner?

Rod.
--
Virtual Access V6.3 free usenet/email software from
http://sourceforge.net/projects/virtual-access/

"Roderick Stewart" wrote in
message .myzen.co.uk...
In article , Bill Wright
wrote:
I do know that when I was at college (in the sticks) our gramphones used
to
have to be set at 78 to play 45s during January. As you will gather none
of
us had perfect pitch.

Wasn't that just to make those awful records you'd been given for
Christmas
finish sooner?

Is was more about pretending to enjoy the Cliff Richard records played by
the girl whose room you intened to spend the night in. Tell you something
though, after three hours of Cliff Richard and Val Doonican it can be a
problem getting a hard on.

Delaney's ****ing donkey! Jesus Christ I've suffered.

Bill

In article , Andy
Burns
wrote:
On 07/09/2008 23:35, Bill Wright wrote:

How does the amount of energy delivered for a given voltage vary with
supply frequency?

Higher frequency waves of same amplitude have higher energy don't they?

Short answer: No. :-)

Longer answer: Depends what you are referring to. But if you mean
conventional electronic waveforms into resistive loads. No. :-)

Slainte,

Jim

--
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Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
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On 09/09/2008 08:36, Jim Lesurf wrote:

In article , Andy
Burns
wrote:

Higher frequency waves of same amplitude have higher energy don't they?

Short answer: No. :-)

Longer answer: Depends what you are referring to. But if you mean
conventional electronic waveforms into resistive loads. No. :-)

I recall from O Level physics that it does apply for longitudinal waves
(the example given was a woman with a high pitch voice imparting more
energy than a man with a low pitch voice) and from what I could find
before posting the above it seemed to apply to electromagnetic waves too

http://csep10.phys.utk.edu/astr162/l...ght/waves.html

I suppose we were talking about current flow in a conductor, rather than
electromagnetic wave, does wave/particle duality enter into it in that
case?.

Thanks for the answer.

Jim Lesurf wrote:
In article , Andy
Burns
wrote:
On 07/09/2008 23:35, Bill Wright wrote:

How does the amount of energy delivered for a given voltage vary with
supply frequency?

Higher frequency waves of same amplitude have higher energy don't they?

Short answer: No. :-)

Longer answer: Depends what you are referring to. But if you mean
conventional electronic waveforms into resistive loads. No. :-)


Electronic waveforms into resistive loads are IMHO a special case. It's
rare to find a system like that where resonance is unimportant. It's
certainly not the case for the mains system, where there are lots of
capacitative loads, inductive loads, and hundreds of miles of
transmission lines.

Andy