Of Energy and Power - Watt, Watt-hour, joules

Several years ago, our government canceled the unit as well, and other heat energy metrology like calorie to be denied as well, instead of watt. But in the ordinary life we used to use it as our lighting consume unit. Our Chinese call it "du", je. Watt*hour. When we fill out bill, we put down numbers "du".

Hi CNPOWER!!

But is watt-hour not a unit of Energy...Electrical Energy....

And is it wrong..... then how?? I accept it is not an SI unit of Energy.. But it is the same as representing energy as joules...

Your math is correct. Energy is the product of power and time, period. Any power unit multiplied by any time unit IS a measure of energy, although not necessarily a traditional one in any given location or for a particular kind of energy.

Although, at least in the USA, the Watt (and its combinations with various metric prefixes:k,M,m,etc.) is the traditional unit for electrical power, there is no mathematical reason we could not rate internal combustion or other engines in Watts, kW, etc. So strictly speaking, the Watt is a unit of power (rate of energy consumption or production), not just electrical power.

Im glad to answer again.
first of all, I have to modify my error description of "du". in chinese it means "thousand watt hour", I leak a letter "k".
As dkwarner point out again: energy is product of power multiply time. But watt hour is really not a unit of International unit system. its only convinient representation for people use somewhere and some times in ordirary life. We can review our physics knowledge, we know htere are many unit systems. but we use most is MKgSA unit system. i.e. meter, kilogram, second and ampere unit system.[ of cause cm.g.s.a is also most use in science]. in this basic unit, energy is represented as Joule. as we all kow. and Joule = watt*second.

cont..

In our life we frequently use power representing our do work mahcine. say the generator has 1kw or the lamp is 300w. As the electric enery is tied up with our life, especially lighting iterm. When we have to pay for our electric energy. we use to say how much watt hour we used. of cause we can say watt second as well, but its too small to convinient representation.
there are many other units use in our folk custom. for instance, I said heat unit, carolie, is anohter one example.
In international metrology organization, they define many standard units for our normal use. we say them normal unit. As the watt hour is not in the standard draft, we call its informal unit. although we use it in our life even frequently. and it does be able to calculate energy.
now i think you will understand what is standard unit, what is not. and you will not quarry about it.
In fact you can list many other units you use them frequently. some in your country others in other countries. if you are interesting in. pls try!

As you know, watt is the derive SI unit of power, real power particularly.

When you see 200W load rating, it doesn't mean 200Wh, you have to check the efficiency, says 75%, that mean you will need around 267W, in this step you can say that 200W load with efficiency 75%, it consume 267WH, or 961.2kJ.

Suppose your machine efficiency is 100% (not in real life), you just need 200WH or 720kJ as you explained.

Watt hour is electrical energy, watt is SI derivation, but hour is not.

Joule is mechanical energy, N-m = Force of one newton in one meter. Also defined as C-V = work require/energy to move electric charge one coulomb through potential different 1 Volt. Also W-s = Work done to produce one watt continously for one second.

So both Joule and W-H are unit of energy. Joule play in the mechanical term, while watt-h in electrical term. I think the representation of electrical energy in watt-hour is correct, or may be someone have better explanation.....

This is similar to stating that the light-year is not a unit of distance or there are not pi diameters round the circumference of a circle. There must be more to life than debating all this...

Reply to #5 - hear-hear! I think it's time Vish found a different friend, one with a more scientific attitude!

Well put Guest on post #5. Units are units, the whole concept was created to help us measure and quantify things. As long as it's done correctly you can change them around to suit whatever your system needs. MPH or KPM must not be units of speed either; we should be using ft/sec or m/s on speedometers (sarcasm). Now there is something to be said about for standardization of units, but it should not get in the way of productivity. By the way, how much energy is in a lb of steam??

There is absolutely nothing wrong with using watt-hours as a unit. People who cry otherwise need to loosen up and realize that numbers can be reduced and simplified into more manageable units. No one describes longer periods of time using seconds. They use hours. As such it is only sensible that your energy consumption units be related to hours. So long as your conversion factors are correct you can use watt-fortnight for all I care. Your answer of 200 watt-hours is 100% correct. On the same token, 720,000 watt-seconds is also 100% correct. It is a lot easier to say 200 watt-hours though.

You are correct that numbers and units can and should be manipulated for convenience, but there is a flaw in the term watt hour. a watt is a joule per second (j/s) and multiplying that by hours is not appropriate. the term watt-hour is really (j*hour/s). The time units should cancel out to leave you with joules which is a unit of energy. Energy ratings should calculated as joules, kilojoules and megajoules which can be used accordingly to the convenience of the application. This would be the correct and quantifiable energy termenology.

200 watt-hours or 720 Kj

Some how I think the latter is easier.

1. says that the notation watt-hour is not the proper way to denote the Energy consumed by the system

We both accept that watt-hour is not an SI sytem unit... But 1. goes even further to state that it is not a unit of Energy.....

The other posts are very correct. I am not anything near as informed, but; I would think that if using seconds to do the math is an SI unit, then using hours is too. I got the idea that secconds were ok to the SI system. I could be wrong, after all my country still uses Imperial. Stupid Americans, with all love and patriotism.

"Correct" is a social construct and is purely a matter of opion. Mathematically as you pointed out, a watt-hour is without a doubt a "measure" of energy. However to call it a unit I suppose could be argued becusae "unit" is singular and "watt-hour" it is really made up of two unitS (plural) "watts" and "hours".

You (and vicariously, your friend) wrote: "We both accept that watt-hour is not an SI system unit... But 1. goes even further to state that it is not a unit of Energy.....

That is something we both do not accept...."

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Power is the rate at which energy is transferred to the load, just as velocity is the rate at which distance is traversed. To get the amount of energy transferred over a certain interval, you integrate the power with respect to time. To get the distance traversed over a certain interval, you integrate the velocity with respect to time. From a purely mathematical perspective, the two problems are identical.

As your 200-watt load represents a constant rate of energy consumed, integrating this rate over an interval (here, one hour) reduces to multiplying the rate times the duration of the interval:

Power = Energy/time,

By re-arranging the terms we have:

Energy = Power * time.

I accept that 'watt-hour' is not an SI system unit... But my friend, #1, goes even further to state that it is not a unit of Energy.....

I disagree.

Consequently, to placate my friend I not only convert watt-hours to SI units, but show that watt-hours and joules are both units of Energy and differ only by a constant scale factor. Hence:

Energy = 200 watts * 1 hour

Energy = 200 watt-hours

Energy = 200 watts * 1 (joule/sec)/watt * 1 hour * 3600 sec/hour

cancelling terms, we have,

Energy = 720,000 joules,

hence,

Energy = 200 watt-hours = 720,000 joules.

hence,

Joules and watt-hours are both units of energy. That one is an SI unit and the other is not is irrelevant. That one is preferred over the other is a matter of convenience, tradition, simplicity, necessity, personal choice, or whatever, does not change the fact that both are expressions of energy. Period. They differ only by a constant scale factor:

1 joule = 1 watt-second = 1/3600 watt-hour,

and conversely,

1 watt-hour = 3600 joules.

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Instead of energy, let's talk about distance. I live in the United States which, despite its loud and boisterous claims of being the most Advanced Nation on Earth, still subscribes to the Imperial System of measurement: inches, feet, yards, miles, ad nauseum. Every nation has its blind spot(s). (Most of them are in Washington, D.C., but I digress...)

Let's say I'm driving my car (a blueprinted, fully-blown, nitro-injected 1989 Lamborghini Countach) at a constant velocity of 200 miles per hour. I have a Pink-Slip Daddy, Mum's the State Attorney General, I have lots of straight-as-an-arrow West Texas highway in front of me, and so I let the horses run free for exactly one hour. Any longer than that will piss too many people off.

As my 200 mph velocity represents a constant rate of distance traversed, integrating this rate over an interval (here, one hour) reduces to multiplying the rate times the duration of the interval:

Velocity = Distance/time,

By re-arranging the terms we have:

Distance = Velocity * time.

I accept that 'mile' is not an SI system unit... But my friend, #1, goes even further to state that it is not a unit of Distance.....

I disagree.

Consequently, to placate my friend I not only convert miles to SI units, but show that miles and meters are both units of Distance and differ only by a constant scale factor. Hence:

Distance = 200 miles/hour * 1 hour

Distance = 200 miles

Distance = 200 mi * 5280 ft/mi * 12 in/ft * (exactly) 2.54 cm/in * 1 m/100 cm

cancelling terms, we have,

Distance = 321,868.8 meters.

hence,

Distance = 200 miles = 321,868.8 meters,

hence,

Meters and miles are both units of distance. That one is an SI unit and the other is not is irrelevant. That one is preferred over the other is a matter of convenience, tradition, simplicity, necessity, personal choice, National Inertia, or whatever, does not change the fact that both are expressions of distance. Period. They differ only by a constant scale factor:

1 meter = (1/1609.34) miles,

and conversely,

1 mile = 1609.34 meters.

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Does this help?

-e

no wonder you guys' crashed a satillite on Mars. Pick a unit of measure and stick with it. Besides in the United States,I belive Amps*Volts still = Watts. Watts/740= Horse Power and I don't want my 500HP Mustang Santa is bringing, rated in joules,kilowatts or anything metric!

You wrote: "Pick a unit of measure and stick with it"

The problem was not one of units, but one of engineering and engineering-management incompetence.

-e

WHOA..............Electrical Engineers are going to love this one...........I'm with shart4legged.............electrical equipment is designed, manufactured, sold-bought,installed and used and it is rated by U.L. Lab. in volts, amps and watts. Our elctric service meters integrate volts-amps-hours and spits out watt-hours or, kilowatt-hours.......GOOD OLE U.S. of A.

Old F**t wrote: "...electrical equipment is designed, manufactured, sold-bought, installed and used and it is rated by U.L. Lab. in volts, amps and watts. Our elctric service meters integrate volts-amps-hours and spits out watt-hours or, kilowatt-hours..."

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Those are units I've always used, too, and I really couldn't care less if they're SI units or not. If the utility company wants to bill me in kJ rather than kWh, c'est la vie!

Cheers!

-e

"...I don't want my 500HP Mustang Santa is bringing, rated in joules,kilowatts or anything metric!"

Would that figure be:

500 (550 ft-lbf/s) Horsepower?

500 Water Horsepower?

500 British Horsepower?

500 Cheval-Vapeur Horsepower?

500 Boiler Horsepower?

or

500 Metric Horsepower? (Oops! you said "I don't want...anything metric")

-e

The old fashioned way

Power=WORK/time=force*distance/time= (180Lbf)(2.4*2PI*12ft)/1min

or 33,00ft-Lbf/min.

Speaking of horsepower, NIST maintains fundamental standards for time, length, mass, and other units. But does NIST have a farm on which they maintain a Standard Horse?

Have a great Christmas!

-e

Hi Europium.... but is HP metric...

NO!

SI unit of power is the

WATT or multiples thereof i.e.

yw zw aw fw pw nw μw mw kw Mw Gw Tw Pw Ew Zw Yw

and if one of those doesn't fit you must be in another universe.

Merry Christmas Masu! Hope Santa was good to you and yours!

Did Mrs. Claus leave behind any fine Plössl eyepieces for your new acquisition?

If only we could be so lucky.

Sometime in the night this great big jolly fat bastard showed up in a fake sleigh (reeking of diesel and badly in need of a valve job), plundered our tree (laughing the whole time), and left behind nothing but a lump of coal. Mic-equipped IR security cams caught the whole thing.

You know, I bet he was some crazy cajun from down Louisiana way. In fact, I'm sure of it. I'd know that sadistic "Heaux! Heaux! Heaux!" anywhere.

-e

Hi e,

No unfortunately. I did however get 2 copies of the same book on astronomy so I guess everybody is thinking along the correct lines.

The sky finally cleared and I got a couple of hours observing in before the batteries gave out. Today's project is the construction of a 12V power supply in an attempt to prevent this serious annoyance from reappearing. I was surprised at the number of man made objects as I saw, two satellites cross the field of view just by chance. This sort of worries me a bit as it implies that space is becoming seriously congested.

Even with the 25mm eyepiece I currently have Saturn and its moons are quite spectacular, I'm looking forward to when I have some shorter eyepieces and the rest of the planets are better aligned. I removed the lens from my old digital camera and played around with the camera port and managed to get one image with a yellowish blob on it so I am confident that with the correct adaptor I can get a half descent image. But that's all in the future.

Hope you had an enjoyable Christmas and have a prosperous and happy New Year.

Masu wrote: "I removed the lens from my old digital camera and played around with the camera port and managed to get one image with a yellowish blob on it so I am confident that with the correct adaptor I can get a half descent image. But that's all in the future."

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Hi Masu,

Something to be aware of when using color CCD cameras for astrophotography is that if your camera uses a single-chip color CCD imager (most do), your resolution will be significantly reduced over that of a monochrome CCD chip having the same number of pixels. Where a monochrome CCD chip uses one physical light sensing element per pixel, a color CCD chip uses three elements per pixel: one each for red, green, and blue. As CCD chips really don't see in color, the chip is overlayed with a so-called Bayer Filter:

The smaller features in an image may strike only one or two elements giving a false color. In the particular filter configuration above, you'd see the feature in yellow (r+g), cyan (g+b), blue, green, or red. The filter also absorbs a significant amount of light, reducing the chip's overall sensitivity to very faint objects. Some chips (like the one in my camera) are overlayed with an additional filter to reduce IR sensitivity.

Your best bet, I think, is to start with a monochrome CCD camera tailored for astrophotography. Sometimes these come with software that lets you integrate exposures over time (which enhances faint objects while at the same time reducing noise (due in part to each element's dark current). More expensive CCD cameras feature cooled CCD chips to reduce the dark current. Usually the cooling is done by means of Peltier stacks.

An overview of CCD cameras for astrophotography can be found here.

-e

Hi e, I knew there were limitations that come with CCD devices but havn't thought too deeply on the subject yet. I do have an old 35mm SLR camera body that might be worth using as well. I was fairly heavily into photography in my younger years and still have most of the kit to process films etc. What do you think is best to use monochrome film in negative format or colour transparency film? I also have access to an HP scanner that can scan slides and negatives so transferring them to a digital format later isn't a problem. Trouble all my kit is still in Adelaide and I won't get back till end of January at the earliest. After that its going to be hectic as we will be moving back to Sydney on a permanent basis. That means packing up two decades of accumulated goodies and just thinking about it nauseates me. There are over 1,000 books alone so you can imagine how much other junk we have accumulated.

The CCD devices Meade sell to go with the telescope are I believe monochrome and have a resolution of 750K pixels. The digital camera I have has a 1.3M pixel resolution so at a quick guess its going to need 6 times as much light to work. One plus is the IR filter in the lens and I checked too make sure there was no additional filter built into the chip by shining an IR remote control at the chip, in a dark room, and snapping a picture. The poor old CCD had a coronary, which would indicate no further IR filter. Since the camera port on the telescope requires no additional lenses to form an image I can completely ditch all the camera optics and just use the CCD and circuitry to get an image. I can pull the camera apart so it may be possible to modify it, maybe putting a heat sink on the CCD would keep it as cool as possible and reduce the noise.

I agree that the best way to go would be to get a the proper device to go with the telescope. I would probably be pushing my luck beyond its breaking limit so it will need to wait a little till I sneak it onto the "You know what I could really use list". For the time being I will need to stick with the camera I have. I read an article the other day on the Cannon EOS 20Da that has been re-engineered specifically for use as an astronomical camera. Since it can also be used a standard DSLR it might be easier to convince the other half that it's a good investment rather than one that can only be use for astronomy.

The book says that you will get 20 hours out of a set of batteries but that's when its tracking a star and doesn't take into account the drain when you are moving it. The result is if you start looking at multiple targets is chews batteries like they are going out of fashion. I half way through building a power supply so hopefully I will solve that problem today.

I havn't looked for a good astronomy site on the WWW yet so do you have any suggestions on a site that worth scrutinizing that keeps people abreast of things worth looking at?

Masu wrote: "I haven't looked for a good astronomy site on the WWW yet so do you have any suggestions on a site that worth scrutinizing that keeps people abreast of things worth looking at?"

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If I were to visit Australia (some day hopefully) the very first thing I'd point my scope at would be the star Eta Carinae and its surrounding nebula NGC 3372., located at RA (Right Ascension) 10^h 45.1' and Dec (Declination) -59° 52'. (Your scope allows you to punch in these values directly, if I'm not mistaken.) E.C. (the star) is located very near the Keyhole Nebula embedded within '3372. Here's an overall view of the nebula from your neck of the woods. In this view, EC is the bright star at the 2 o'clock position:

There is evidence that Eta Carinae may actually be a binary system. Every five and a half years or so E.C.'s spectrum shifts somewhat and then returns to normal - a dead giveaway for an orbiting companion, may God have mercy on its poor blasted soul. Overall, EC is a naked-eye object with a yellowish-white color. Btw, if EC goes supernova - which it could at any time - it could very well be brighter than a full moon. EC is extremely unstable, so who knows? Also, in spite of its 8000+ light-year distance, EC is easily visible because it emits more energy in 6 seconds than our Sun does in an entire year.

The next thing I'd explore is the LMC (Large Magellanic Cloud) with its plethora of nebulosities, clusters, etc.; including the beautiful Tarantula Nebula, NGC 2070, located at RA: 5h 38.7', Dec: -69° 6'.

Here are some additional links which may interest you:

Meade Cameras for Astrophotography (My first choice would be the DSI Pro with RGB filter kit. Second choice is DSI w/o RGB filter kit).

Digital Camera, CCD, or Film?

CCD Astrophotography WebRing

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My older brother lives in a remote part of Colorado. A few years ago he bought an 8" SCT. Like yours battery life was a problem, so we installed a cold-weather car battery in a small enclosure near his observing site (presently just a concrete pad he poured for his tripod. I hate tripods). I supplied a 15-watt photovoltaic panel with a lead-acid battery charger module to keep the battery topped-off.

A more portable high-capacity battery you might consider getting is one of those "gel-cells" used in toy cars kids (sit in and) drive around the yard. Most of batteries are 6V units, but I've sometimes seen 12V units as well. Or, if you can park your car close enough, you can use a cigarette-lighter adapter to power the scope.

Finally, as your scope probably has an alt-az, or fork, mount, be aware that as the scope tracks an object across the sky, the image will rotate in the camera's field of view. This trait makes such mounts impractical for astrophotography unless you can compensate for the rotation somehow. The simplest (and most reliable) method is to use an equatorial wedge., An equatorial wedge converts your fork (alt-az) mount into an equatorial mount in which the scope turns on an axis parallel with the Earth's axis of rotation. The down side of this is that your computerized mount still assumes it's an alt-az device and won't point your scope in the right direction. It is possible, however, that mfr's of these mounts can allow the user to switch between alt-az and GEM (German Equatorial Mount) modes to allow use of a wedge. You'd have to check your scope's documentation.

Motorized image (de-)rotators are another option, but these are expensive, require a high degree of precision (both in construction and motion control) and don't always do the best job.

As a courtesy to others on this thread, we probably should take this discussion offline. I'll email shortly.

Cheers!

-e

okay guys I don't know how we got on astronomy but lets open a thread. I live in rural colorado, have a 4.5 in reflector and a friend with a home ground 21in reflector. Does anyone know an easy way to columinate? I am having a hard time without lasers etc. A few good websites are Space Weather.com Cloudbait.com(especially if you live in colorado) all the nasa sites (nasa.gov) SOHO.gov APOD.com (be ready to spend an hour or two there) I can go on. email me at shart4legged@yahoo.com or keep watching CR4.

Hey Shart! Thanks for the links, I'll check 'em out.

A home-ground 21" reflector? Even a 12" pyrex blank is very hard to grind and figure by hand. 12" is pretty much at the limit of what most amateur telescope builders can manage without some kind of mechanical assistance. I'd be very interested to see how this was done.

-e

yep 21" home ground, retired gentleman, former Lockheed illustrator with a lot of patience. Forward silvered of course, twice. The man is not a mechanic and although I didn't get to watch the process, I believe he did it by hand.

Hi shart4legged, e is helping me with my latest acquisition of an astronomical telescope and since I am a complete novice I need a lot of help. If you wish to talk to me directly you can send an email via the CR4 server by clicking on my name in any of the discussions then selecting the send mail to link. That way you don't need to advertise your email address to the world, if you do I will send you my direct address. I think we have chased all the unscrupulous mongrels away but you never know.

21" (533mm) is one thumping great mirror and I would also be interested in how he did it. I think I will stick to my 127mm Cassegrain, I'm fairly determined sod but I think grinding a 21" mirror would break my resolve.

Since there are at least 3 astronomers here at CR4 maybe its time we asked if we could have an Astronomy section? Astronomy is a branch of physics and you need to apply it to build and use telescopes so that makes it engineering in my book.

not really worried about the email address going out, I have enough protections in place to thwart almost any attack. Yes, a sight for astronomy here would be nice. I bet there are allot more subscribers interested than just three. As soon as this latest blizzard passes, I will get back to collimating my scope. I don't know what kind of funds you have for your endeavor but I hope you are adept enough to just purchase a good mirror and then build the tube and other optics. There is allot of stuff out there relatively inexpensive. Of course check ebay I will get back with some other sights. good luck and happy new year

My darling wife got me a 127mm x 1900mm Cassegrain telescope with a computer controlled mount for my birthday/Christmas present so I don't need to worry about the fiddly bits for the time being. Next expense is a camera mount so I can take some pictures and post them here at CR4.I have been experiencing the same problem you are with it being solidly overcast for all but a couple of hours since it arrived. The same thing happened with the recent transit of Mercury. I got a new solar filter and built a special adapter and camera mount for an old telescope that I had lying around. It bloodywell rained for the entire transit. Just as the transit finished the rain stopped and the sky cleared within an hour. I was not happy. You and e might be interested in this site

http://antwrp.gsfc.nasa.gov/apod/astropix.html

They have a new astronomy related picture each day so its worth putting on your favorites list and having a quick look whenever you remember.

Hi Sorry that I am replying to this so late..... Well my reply at #23 was a remark at the reply on #17. Well thanks for the conversion tips.... Have a nice day... and please... I am posting a new query. Kindly have a look on that.... Take care.....

You wrote: "Hi Europium.... but is HP metric..."

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But?

-e

Don't you and your friend have better things to do?

No!

But we'er not the ones that take close to a year and a half to read the thread.

That was the best we could do at that point of time....