In article ,
Keith G wrote:
Even leaving items like projectors plugged in can cost you a 200+ quid
lamp - had a ten minute power cut here the other night (according to
some of the clocks) and the next evening the PJ was dead.....

Did the power coming back on switch on the projector? My DLP set will
react to any suddenly active video input by switching out of standby. But
not if it's switched off - rather than unplugged.

--
*Generally speaking, you aren't learning much if your lips are moving.*

Dave Plowman London SW
To e-mail, change noise into sound.

Don Pearce wrote:
On Mon, 21 Aug 2006 08:33:26 +0100, Rob
wrote:

Don Pearce wrote:
On Sun, 20 Aug 2006 22:38:31 +0100, Rob
wrote:

Um - per means 'for each', unless you have a more accurate definition.
You told me to use 'for', or 'FOR', in the first place. Each means every
one of more. Don't mean to patronise ...
Per means divided by. The sum you are doing is multiplied by. You are
talking Watt Hours, not Watts per hour.

d

I meant 'per' in the context of 'for each' - wasn't that clear to you? I
hope you're not a maths or English teacher - would you really say 'six
per three equals two'?

Rob

"For each" is exactly the meaning of per, and that is why you have it
wrong. Suppose you buy 10 apples for 30 pence, that is three pence per
apple (for each). You do that sum by dividing 30 by ten. So Watts per
hour is Watts divided by hours. You need Watts MULTIPLIED by hours,
which is Watt Hours.

I'm not being pedantic - you are not just a little bit wrong, you have
it entirely upside down.

d


Well, I meant multiplied, but you've taken the word 'per' to mean
'divided' which I think you're always going to have difficulty
explaining to me - but thanks for trying. It's curious that you think
that I don't know the difference between multiply and divide - I do by
the way, picked that one up.

The point, that I should have expressed consumption as kWh, and not
watts per hour, is taken. Am I allowed to use the term Wh' BTW?

Rob

Jim Lesurf wrote:
In article , Rob
wrote:


Er, it was! Have I misunderstood something - wouldn't be the first/last
time :-)

I mean he consumes 400 Watts of electricity in one hour. Stand corrected
awaits ...

The nominal unit of energy is the Joule.

Power is the *rate* of energy transfer/creation/loss.

1 Watt (power) is 1 Joule per second (energy per time period).

Thus saying "watts per hour" implies "1 Joule per second, per hour", which
may be gibberish as it is neither a power nor an energy.

Thus the Watt-hour is also a unit of energy since it is the number of
joules transferred/created/used if you use power at the rate of 1 joule per
second for 1 hour. The common unit is the kWh.

Hence it isn't clear what something like, "he consumes 400 Watts of
electricity in one hour" actually means.


I think if forced, under considerable duress and on pain of death, you
could (on a good day) guess what was meant :-)

Am I allowed to say Wh - would that be ambiguous?

Rob

On Mon, 21 Aug 2006 13:36:20 +0100, Rob
wrote:

Don Pearce wrote:
On Mon, 21 Aug 2006 08:33:26 +0100, Rob
wrote:

Don Pearce wrote:
On Sun, 20 Aug 2006 22:38:31 +0100, Rob
wrote:

Um - per means 'for each', unless you have a more accurate definition.
You told me to use 'for', or 'FOR', in the first place. Each means every
one of more. Don't mean to patronise ...
Per means divided by. The sum you are doing is multiplied by. You are
talking Watt Hours, not Watts per hour.

d

I meant 'per' in the context of 'for each' - wasn't that clear to you? I
hope you're not a maths or English teacher - would you really say 'six
per three equals two'?

Rob

"For each" is exactly the meaning of per, and that is why you have it
wrong. Suppose you buy 10 apples for 30 pence, that is three pence per
apple (for each). You do that sum by dividing 30 by ten. So Watts per
hour is Watts divided by hours. You need Watts MULTIPLIED by hours,
which is Watt Hours.

I'm not being pedantic - you are not just a little bit wrong, you have
it entirely upside down.

d


Well, I meant multiplied, but you've taken the word 'per' to mean
'divided' which I think you're always going to have difficulty
explaining to me - but thanks for trying. It's curious that you think
that I don't know the difference between multiply and divide - I do by
the way, picked that one up.


No, I didn't think you couldn't tell the difference between divide and
multiply. I thought you didn't understand the mathematical meaning of
the word "per". Such has proved to be the case.

The point, that I should have expressed consumption as kWh, and not
watts per hour, is taken. Am I allowed to use the term Wh' BTW?

Wh is just fine.

d

--
Pearce Consulting
http://www.pearce.uk.com

On Mon, 21 Aug 2006 13:42:31 +0100, Rob
wrote:

Hence it isn't clear what something like, "he consumes 400 Watts of
electricity in one hour" actually means.


I think if forced, under considerable duress and on pain of death, you
could (on a good day) guess what was meant :-)

The problem with saying you consume 400W of electricity in one hour is
that there is instantly a corollary, which it that you will thus
consume 800W in two hours, and so on. Do you see the problem?

d

--
Pearce Consulting
http://www.pearce.uk.com

In article ,
Rob wrote:
Jim Lesurf wrote:
[snip]

I think if forced, under considerable duress and on pain of death, you
could (on a good day) guess what was meant :-)

Are you unclear on the distinction between 'energy' and 'power'? If so,
then the units used may well confuse.

Am I allowed to say Wh - would that be ambiguous?

For what? :-)

If you mean 'Wh' to mean 'Watt-hour' then this is a unit of energy. It
represents the energy conveyed/used if you consume power at the rate of 1
Watt, for a duration of 1 hour.

So if you have a light bulb rated at '100W' it will use up 1 kWh if you
leave it on for 10 hours. You then pay for energy (numbered in an amount of
kWh). A 50W light would have to be on for 20 hourse to use up 1kWh of
energy.

Also, imagine you have two immersion heaters. One 1 kW, the other 2 kW.

With perfect insulation, the 2kW heater will heat up a tank of water in
half the time that the 1kW heater will require to get the same rise in
temperature. But the amount of energy used will be the same whichever you
used. (In the real world, the insulation won't be perfect, so it won't be
that simple. However physicists are allowed to do things like ignore all
such annoying complications when trying to explain something. :-) )

Slainte,

Jim

--
Electronics http://www.st-and.ac.uk/~www_pa/Scot...o/electron.htm
Audio Misc http://www.st-and.demon.co.uk/AudioMisc/index.html
Armstrong Audio http://www.st-and.demon.co.uk/Audio/armstrong.html
Barbirolli Soc. http://www.st-and.demon.co.uk/JBSoc/JBSoc.html

Jim Lesurf wrote:
In article ,
Rob wrote:
Jim Lesurf wrote:
[snip]

I think if forced, under considerable duress and on pain of death, you
could (on a good day) guess what was meant :-)

Are you unclear on the distinction between 'energy' and 'power'? If so,
then the units used may well confuse.


Well, energy is power; power is the exercise of will :-)

Am I allowed to say Wh - would that be ambiguous?

For what? :-)


Just as a unit of energy, no more, nothing flash.

If you mean 'Wh' to mean 'Watt-hour' then this is a unit of energy. It
represents the energy conveyed/used if you consume power at the rate of 1
Watt, for a duration of 1 hour.

So if you have a light bulb rated at '100W' it will use up 1 kWh if you
leave it on for 10 hours. You then pay for energy (numbered in an amount of
kWh). A 50W light would have to be on for 20 hourse to use up 1kWh of
energy.

Also, imagine you have two immersion heaters. One 1 kW, the other 2 kW.

With perfect insulation, the 2kW heater will heat up a tank of water in
half the time that the 1kW heater will require to get the same rise in
temperature. But the amount of energy used will be the same whichever you
used. (In the real world, the insulation won't be perfect, so it won't be
that simple. However physicists are allowed to do things like ignore all
such annoying complications when trying to explain something. :-) )


Yes, many thanks - I worked on HEES for a couple of years so I am
familiar with what you're saying. That was more to do with fuel poverty
though - not nomenclature. You've all certainly driven home the
importance of precision here so I won't be using the phrase 'Watts per
hour' when I mean Wh.

Phew :-)

Rob

Don Pearce wrote:
On Mon, 21 Aug 2006 13:42:31 +0100, Rob
wrote:

Hence it isn't clear what something like, "he consumes 400 Watts of
electricity in one hour" actually means.

I think if forced, under considerable duress and on pain of death, you
could (on a good day) guess what was meant :-)

The problem with saying you consume 400W of electricity in one hour is
that there is instantly a corollary, which it that you will thus
consume 800W in two hours, and so on. Do you see the problem?

d


Yes, that's quite clear, thanks Don.

Now, on pain of death I take it your answer to the question "If you had
to guess, if someone used the phrase 'Watts per hour', what do you think
they meant?" is:

---

The problem with saying you consume 400W of electricity in one hour is
that there is instantly a corollary, which it that you will thus consume
800W in two hours, and so on. Do you see the problem?

---

In other words, you have absolutely no idea - not even a remote clue, it
would never occur to you that Wh is the answer.

Blimey :-)

On Mon, 21 Aug 2006 18:08:19 +0100, Rob
wrote:

Yes, that's quite clear, thanks Don.

Now, on pain of death I take it your answer to the question "If you had
to guess, if someone used the phrase 'Watts per hour', what do you think
they meant?" is:

I wouldn't have the slightest idea. I would have to assume that they
hadn't either.

---

The problem with saying you consume 400W of electricity in one hour is
that there is instantly a corollary, which it that you will thus consume
800W in two hours, and so on. Do you see the problem?

---

In other words, you have absolutely no idea - not even a remote clue, it
would never occur to you that Wh is the answer.

Blimey :-)

Not really. As I said above, if somebody gave a figure in Watts per
hour, and particularly if they persisted in doing so in the face of
multiple questions, I would assume they had not the slightest clue,
and the figure was therefore devoid of meaning.

Before anyone gets picky, there is of course a circumstance in which
the figure would make sense. It would be if they were talking about a
power generator that was ramping its power upwards at a rate of 400
watts per hour. I take it you don't have such a machine in mind?

d

--
Pearce Consulting
http://www.pearce.uk.com

On Mon, 21 Aug 2006 18:02:15 +0100, Rob
wrote:

Jim Lesurf wrote:
In article ,
Rob wrote:
Jim Lesurf wrote:
[snip]

I think if forced, under considerable duress and on pain of death, you
could (on a good day) guess what was meant :-)

Are you unclear on the distinction between 'energy' and 'power'? If so,
then the units used may well confuse.


Well, energy is power; power is the exercise of will :-)

Now now. Power is the rate at which energy is delivered. :-)

d

--
Pearce Consulting
http://www.pearce.uk.com