Talk:Watt/Archive 1

Archive 1

old comment

I don't think a minor character in a video game is worthy of being mentioned at the top of this page.

— Preceding unsigned comment added by 66.102.74.122 (talk) 19:52, 26 September 2004 (UTC)

Dosage

Can someone who knows (you sparkies out there) add something on this page about lethal wattage, it is wattage that determines tissue damage isn't it?

Lethal "dosage" is complicated because the frequency of the electric current changes the effects on the human body. For example, you can be struck by a lightning bolt which has an incredible amount of power, and walk away with a few burns, or you can accidently touch a live wire cycling at 60 Hz and find that your muscles are unable to let go because the frequency keeps telling your muscles to clench, including your heart (killing you). I think I once saw a chart - DC is the least dangerous frequency, and the danger for the same Voltage increases to about 100 Hz, and then actually goes down a little and then levels off. I could be completely wrong about that though. Oh and one more thing - the statement "it isn't the voltage that kills you, it is the current" is completely wrong as far as I can tell. What typically kills people who are electrocuted is a heart attack. The electricity doesn't cook you, it just interferes with your body's signals until you don't work anymore. --Ignignot 14:47, 5 December 2005 (UTC)

This is probably not the whole story. I read in a newspaper a while ago that a "train surfer" was literally burnt to ashes in an instant when he came too close to the overhead line. I guess in this case the power mattered. (He might have been dead because of a heart attack half an instance earlier, though.) And also the voltage mattered: He didn't need to touch the wire because the distance a spark can travel depends on the voltage. --史慧开 (talk) 13:43, 20 April 2009 (UTC)

Volt-amps

what is the relation between KW & KVA

How do watts relate to volt-amps?

1 Watt = 1 Volt·Amp

Likewise, 1 kW = 1 kVA - Omegatron

Not so (at least in the normal usage). See power factor for the full explanation. 18.26.0.18 04:11, 3 Feb 2005 (UTC)

Yeah, I forgot. I hated that class. :-\ - Omegatron 05:45, Feb 3, 2005 (UTC)

In fact, if you derive the dimensions of both Ampere and Volt you will get the dimensions of the Watt, but I know the point about the difference between the real power and apparent power in AC circuits, however, in the same way that you can say that a Couloumb is an 'Ampere per second', you can also say that a Watt is a VA. Of course that you must pay attention to the context, but it isn't wrong. Afonso Silva 22:00, 19 May 2005 (UTC)

This seems like worthwhile information to place under the "Definition" section of the page. Any reason as to why it's not listed there, or should I add it? -Mbauman 20:11, 21 August 2006 (UTC)

MW*D

I disagree that megawatt days are a common method of reporting power output of power plants. Typically they are quoted in kilowatt hours, kWh, because that is how they bill their customers. --Ignignot 21:17, Feb 7, 2005 (UTC)

It may vary from country to country. Andrewa 19:12, 4 November 2005 (UTC)

North America uses kWh. I don't know about Europe or Japan or any other country. --Ignignot 14:39, 5 December 2005 (UTC)

Great Britain uses kWh for customer billing. However I don't see any reason why MW days wouldn't be used for power output. Someone find a reference or a power plant manager to confirm. 11:19, 13 March 2006 (UTC)

The EIA quotes in thousand MWh's on their website[1]. The NEB uses kWh, GWh, TWh, etc but not days[2] (pdf). The UK seems to be fond of "Million Tons of Oil Equivilent" which is a bizzare unit of measurement, but occasionally they use TWh [3] (pdf). The IEA (an international organization that monitors energy usage) quotes in GWh [4]. I think that while I have not been able to find non-English sources, I have shown that MW*D are not a common way of reporting power output. They might quote in MW, or kWh or MWh etc. but not MW*D. The only place I could find with reference to MW*d is for measuring the energy content of coal or nuclear fuel, which is more of a heat capacity or efficiency factor, and is extremely specialized. If there are more important examples (like the boilerplate of a generator being quoted in MW*d) then I would say leave it in, but since this method of quoting is so uncommon I'm going to remove it. By the way, I have a degree in electrical engineering and I work as an energy analyst, so I have some idea of what I'm taking about. --Ignignot 22:02, 13 March 2006 (UTC)

In relation to speakers and the like

Just curious what the watts actually do for speakers. Some surround sound systems are 100 watts or less and others are much higher (1000 for example). I imagine that the more watts the more power it all uses, so does that mean that the sound can go louder? or clearer? or what?

Loudspeaker#Efficiency has the answer to this. Also Audio power has a good explanation of RMS and PMPO. --Bkrosnov 11:43, 9 March 2006 (UTC)

1 kW·h = x kJ

There seems to be a bit of a revert war over whether a kilowatt hour is 3.6 MJ or 3.6 kJ. Let's work it out:

1 kW·h = 1000 W × 3600 s = 3,600,000 W·s = 3,600,000 J = 3.6 MJ

Indefatigable 15:15, 27 February 2006 (UTC)

The reason some people construe the kilowatt-hour as 3.6 kJ I noticed is due to the fact that these same people construe 1 kW as equal to 1000 J/ 1000 s , which is wrong. I attempted to solve this earlier by making clear in both the kilowatt and megawatt sections of the article that 1 kW = 1,000 J/s (NOT: 1,000 J/ 1,000s); and for megawatt that 1 MW = 1,000,000 joules per second. If someone were to construe a kilowatt as 1,000 joules for every 1,000 seconds then when that same person multiplies this false rate by 3,600 seconds the end (and false) result will be 3.6 kJ, instead of the correct conversion for kWh, which is 3.6 Megajoules. Therefore the edit made earlier clarifying what 1 kW equals and what 1 MW equals should be left alone and remain in the article. —Preceding unsigned comment added by 128.230.251.148 (talk) 21:38, 27 November 2007 (UTC)

64.185.152.169 —Preceding unsigned comment added by 128.230.251.148 (talk) 21:40, 27 November 2007 (UTC)

Typical household lamp

The intro said "A typical household, incandescent lightbulb uses 100 watts." That seemed way too much, so I changed it to 40-80 W. Or is 100 W normal somewhere? (let me guess - the US?) DirkvdM 08:36, 20 July 2006 (UTC)

That sounds like anti-American bigotry. While 100 Watt bulbs are available, most fixtures limit you 40-75 Watt bulbs. —The preceding unsigned comment was added by Mc6809e (talk • contribs) 01:18, 11 March 2007 (UTC).

100's are common in the U.S., tho getting less so. Are 20 W incandecants common anywhere? Changing to 40 - 100 W. --agr 14:38, 20 July 2006 (UTC)

I’ve been using 15 W incandecants in the US since the late 1970s/early 1980s. I’ve never had trouble finding them. Malirath (talk) 17:56, 18 June 2008 (UTC)

It's "incandescent", not "incandecant". And 15 watts for an incandescent bulb would be very dim indeed. Or did you mean fluorescent? Captain Quirk (talk) 02:15, 14 February 2009 (UTC)

A quick trip to Philip's website reveals bulbs for regular fixtures in 15, 25, 40, 60, 75, 100, 150, and 200W sizes. You can read just fine by a 15W bulb if it's close to the reading material, ie, task-specific, optimized lighting. They're common in ovens and such too. Renegrade (talk) 14:21, 12 March 2009 (UTC)

Excuse my spelling mistake. No I did not mean flourescent. --Malirath (talk) 18:10, 31 March 2009 (UTC)

Kilowatt-hour

kWh is a unit of energy, not power. Maybe it deserves a mention here, with a link to watt-hour, but the long discussion seems inappropriate. The stuff on mixed units of time also seems a bit POV. --agr 14:57, 20 July 2006 (UTC)

POV? How can something like that be pov? It does mix up three units of time, two of which are not SI units. That's worth poiting out isn't it? I won't put it back yet, because I don't feel like a revert war. And why do you point out that kWh is a unit of energy? DirkvdM 06:14, 21 July 2006 (UTC)

No response for about a week, so I'll put it back. DirkvdM 09:46, 27 July 2006 (UTC)

First of all, this article is about the Watt. There is a separate article for Watt-hour, which already points out that Wh is not an SI unit. The term "mix up" is POV because it implies something foolish or improper. The unit is widely used. Since the meter is now defined in terms of light seconds, one could say the same about km/h, I suppose. --agr 21:45, 28 July 2006 (UTC)

If 'mix up' isn't the right terminology, then change that to something that sounds less pov to you in stead of bluntly reverting the whole thing. If an article about an SI unit introduces a non-SI unit then that needs to be pointed out. And if something needs to be moved to another article, then do that, in stead of bluntly reverting the whole thing. In other words, you're not being very constructive. DirkvdM 08:10, 29 July 2006 (UTC)

I don't meant to be harsh, but I think the treatment of the non-SI issue in watt hour is adequate. If you feel additional information should be added, that is the place to discuss it, not here.--agr 03:39, 30 July 2006 (UTC)

Don't worry about my feelings, I've got a pretty tough skin. :) To me, only argumentation counts. Anyway, I still think the Wh/yr should be mentioned here, because it's also a unit of power, and derived from the watt. I'll give the same info in a shorter form, maybe that satisfies you. DirkvdM 11:04, 30 July 2006 (UTC)

MWh/yr seems to be what is used, particularly in alternative energy discussions. I agree it deserves a mention and conversion factor to Watts. There may also be a need to explain the distinction between peak and average power in the article. I wonder if MWh/yr is used in these contexts to make it clear that they are talking about actual energy produced during the year. --agr 19:51, 30 July 2006 (UTC)

Well, whether you use Wh/yr, kWh/yr, MWh/yr or whatever depends on what gives the most convenient values. It's all the same unit, multiplied by a power of 10, just written in a different form. Which is why we have an article on Wh, the basic unit, not the more common kWh. I'm not sure what you mean by that last sentence. DirkvdM 09:33, 31 July 2006 (UTC)

Right, but this article is about the Watt, not "units of power." If another Watt-related unit is to be mentioned at all, I think it should be in its most common form. There are a vast number of possible derived units that might be used somewhere (kWh/acre/month) and we can't cover them all. --agr 15:16, 31 July 2006 (UTC)

By that reasoning the kWh should also be removed. Unless you go by frequency of use. When I Google kWh I get 15 million results. For kWh/yr I get 75 thousand. Quite a lot less, but still rather much. When I Google kWh/acre/month I get none at all. Maybe you used a bad counter-argument because you deliberately exaggerated. Can you think of any better ones? If there is indeed a vast number of derived units that are used as much as kWh/yr, you've got a point. DirkvdM 12:36, 1 August 2006 (UTC)

I don't wish to argue about kWh/day vs MWh/day. Use your judgement. My point is that these are not the subject of the article, so any discussion should be brief.--agr 15:22, 1 August 2006 (UTC)

We don't seem to understand each other. I'm not talking about prefixes but about mentioning another unit than Watt. If there is room for Wh, then there should also be room for Wh/yr. These should be dealt with somewhere and the latter doesn't (yet?) deserve a separate article, so here would be a good place. Anyway, it's short enough now, isn't it? DirkvdM 09:06, 4 August 2006 (UTC)

volts * amps revisited

Mbauman inquired as to why this information wasn't included in the article, and I'm wondering as well. Should I add this information, or is there a specific reason that it has been omited from this article. Perhaps a subsection of conversations and/or relations to other units? RichMac 19:26, 9 October 2006 (UTC)

To review and expand on what was discussed above, the instantaneous power in an AC circuit is constantly changing. For convenience, the power quoted is usually the root mean square]] (RMS) average power. To accurately find the RMS average power, the current and voltage must be measured instant by instant, multiplied to find the instantaneous power, and the average power calculated. It is often more convenient to measure the RMS voltage and RMS current separately, and multiply the results. If the load is a resistor, this will be accurate, but the more capacitive or inductive the load is, the less accurate this approximation is.

When a "power" is given in volt-amperes rater than watts, it is a shorthand way of indicating that the RMS voltage and RMS current were measured separately, then multiplied to estimate the power; no correction for the inductance or capacitance of the load has been made. I think a link should be added to the volt-ampere article.

I fixed this posting after reading Omegatron's post below. --Gerry Ashton 20:56, 9 October 2006 (UTC)

Not "RMS power"; "average power". Average (apparent) power is measured by multiplying RMS voltage and current. — Omegatron 20:28, 9 October 2006 (UTC)

Actually, multplying RMS voltage by RMS current gives apparent power, which is equal to average power only if the load is resistive, but thanks for reminding me about the meaning of average power. --Gerry Ashton 21:00, 9 October 2006 (UTC)

Oh, of course. I work in a world of resistive loads.  :-) — Omegatron 21:05, 9 October 2006 (UTC)

Signal strength(?) vs. field strength

Ignoring gains, losses and free-space loss for the moment, field strength is typically defined as $\scriptstyle {V/m={\frac {V}{4\pi \,m}}={\sqrt {\frac {4\pi 30W}{4\pi \,m^{2}}}}={\frac {\sqrt {30W}}{m}}\,\!}$ or $\scriptstyle {W/m^{2}={\frac {W}{4\pi \,m^{2}}}.\,\!}$ I realize field strength defines the surface area of a "power sphere" (inversely, $\scriptstyle {W={\frac {W}{m^{2}}}4\pi \,m^{2}\,\!}$), but when attempting to define the strength of a signal at a receiver's input point (i.e., antenna connection point), isn't the situation like a ball resting on a flat surface?: The ball's contact to the surface is only at a single point (or very small surface area around the point), not the whole surface area of the ball, thus the more relevant measurement is the "strength/intensity" of the radius touching the flat surface (i.e., the particular "flux line"). Wouldn't the strength of the flux line be $\scriptstyle {{\frac {W}{m}}\,\!}$ and be considered the "signal strength" (signal strength seems to confirm that, but other articles and outside sources seem to use signal and field strength interchangeably)?

Let $W_{l}=W/m={\frac {W}{m}};\qquad \;W_{a}=W/m^{2}={\frac {W}{4\pi \,m^{2}}}.\,\!$

Let's say you have a 100kW station that is 1km away, giving the following results:

100,000W @ 1000m

100Wl

.007958Wa

If you have ten other stations with different ERPs and distances, five equaling W_l and five W_a,

	Line	Area
10,000W @ 100m	100Wl	.07958Wa
1000W @ 10m	100Wl	.7958Wa
100W @ 1m	100Wl	7.958Wa
10W @ .1m	100Wl	79.58Wa
1W @ .01m	100Wl	795.8Wa

	Line	Area
1000W @ 100m	10Wl	.007958Wa
10W @ 10m	1Wl	.007958Wa
.1W @ 1m	.1Wl	.007958Wa
.001W @ .1m	.01Wl	.007958Wa
.00001W @ .01m	.001Wl	.007958Wa

and you measured the strength of the signal right at the antenna connection point (but not through any antenna, just "barefoot") of a receiver, which set of five stations would equal the same strength of the 100kW station, the 100W_l or .007958W_a set? If it is W_l, would it be the same for any antenna attached or, as antenna length/size increases, is that when area (i.e., W_a) comes into play? Now let's say there is an eleventh, distant station, say 500km away (well beyond its prescribed field strength), coming in via unusual propagation——either via tropospheric ducting or sporadic E-skip——wouldn't that be the same 100W_l or .007958W_a?
Finally, incorporating free-space loss (where λ is wavelength), $W/m^{2}={\frac {W}{4\pi \,m^{2}}}.\,\!$ becomes $W/m^{2}={\frac {W}{4\pi \,m^{2}}}\cdot {\frac {\lambda ^{2}}{4\pi }}=W\left({\frac {\lambda }{4\pi \,m}}\right)^{2}.\,\!$.

Does that mean $W/m\,\!$ becomes ${\frac {W\lambda }{{\sqrt {4\pi }}\,m}}\,\!$ or just ${\frac {W\lambda }{m}}\,\!$?
 ~Kaimbridge~15:14, 22 April 2007 (UTC)

Perhaps the talk page for Radio propagation would be a better place to ask this question. --Gerry Ashton 18:02, 23 April 2007 (UTC)

Okay, I'll try over there ~Kaimbridge~16:44, 24 April 2007 (UTC)

Problem

Look for Kelvin in wikipedia. The smaller prefixes do not match (yocto etc.) :S — Preceding unsigned comment added by 194.204.127.248 (talk)

I have checked it and I found no difference. What did you refer? I only see that columns are swapped left-right. Rjgodoy 20:06, 3 June 2007 (UTC)

Science (Journal)

The OED also says "megawatt" appeared in a 28 November 1847, article in Science (506:2).

I was going to change [[Science]] to [[Science (journal)]] but then I noticed that Science (journal) claims, quite believably, that the journal was founded in 1880. Can someone check this OED statement? Mditto 21:03, 17 July 2007 (UTC) The OED cite mentioned is for 1947. I've corrected the date, though I don't really see the point of including the sentence. Dbfirs 18:46, 10 January 2009 (UTC)

SI multiples

I have nominated Template:SI multiples (transcluded or subst'ed in this article) for deletion on WP:TFD. Han-Kwang (t) 16:12, 23 August 2007 (UTC)

To kill a human

Brought this over from the volts page.

What would be the minimum amount of volts to kill a human? I am just comparing the ability of some animals and whether they would be capable to killing a person. Daily Rubbings 16:10, 12 June 2007 (UTC)

Just replace where it says volts with watts.

Voltage is not the lethal part, the ampage is what kills you. ralph86 14 Apr 2009 —Preceding undated comment added 19:42, 14 April 2009 (UTC).

We were told that in electrical classes as well, but medically, it matters little if the voltage is very high, because voltage burns. A high enough voltage, even with less than the said-lethal 10th of an amp (lethal not because it's much but because it's close enough to our hearts' electrocardial level), will simply burn your insides out due to your resistance : ) 80.101.162.155 (talk) 17:35, 14 October 2009 (UTC)

Confusion in introduction

The introduction says that a watt is equal to one joule of energy per second. Isn't it more correct to say that a watt-second is equal to one joule? It's just a little confusing, especially after reading the section about "Confusion of watts and watt-hours". LK (t|c) 22:22, 15 November 2007 (UTC)

I'd say they mean the same. --Gerry Ashton 23:09, 15 November 2007 (UTC)

MWth and MWe

also posted at Talk:Longannet power station

This is a case where the strict usage SI units differs from usage in the electricty industry. As a worker in the UK electricity industry (and having also worked in the North American electricity industry, I recognise MWth and MWe, whilst W_th and MW_e are alien to me. --Stewart ^(talk) 08:58, 14 January 2008 (UTC)

It seems to me that incorrect usage by the electricity industry, if widespread, should be acknowledged. But that doesn't mean that we should make the same mistake ourselves elsewhere on WP. Can you supply a reliable source for this usage? Thunderbird2 (talk) 09:01, 14 January 2008 (UTC)

Here are two for starters CANDU owner's group page for Bruce Power and EDF Nuclear Generation. --Stewart ^(talk) 18:27, 14 January 2008 (UTC)

Thanks. That is already more than there are on this page for MW_e. But they are both from commercial power companies, right? Do you know of an industry standards body or something similar that may confirm your version of these abbreviations?

In parallel, can anyone back up the statement that the correct abbreviation for this quantity is MW_e (and not MWe)? If not, I suggest converting to MWe on the basis of the sources offered by Stewart. Thunderbird2 (talk) 19:23, 14 January 2008 (UTC)

I found this, which further supports Stewart's position. It seems I reverted his changes too hurriedly. Sorry :-(

Notice though that he uses MWt rather than MWth for "thermal". Should both be mentioned? Thunderbird2 (talk) 19:36, 14 January 2008 (UTC)

These are SI units. They're just SI units with labels tacked onto them. A "megawatt electrical" is still a megawatt; the symbol just differentiates which part of the output you're talking about. Same as "volts peak-to-peak", written as V_P-P or "volts rms" written as V_rms. They're still volts. The e and th are not part of the unit; they're labels, which is why they're written in subscript.

It's common in engineering and math to write labels as subscripts when formatting things "properly", but simplify to plain lowercase when lazy or when the medium doesn't allow subscripts. "V_out" becomes "Vout" for instance. I think that's all that's going on here. For example, in [5], they use "GW_eyr" in the main text, but simplify to "GWeyr" on a chart's axis, presumably because their chart-plotting program doesn't support subscripts there. This isn't standardized that I'm aware of; MW(e) is another way to write it without subscripts.[6] [7]

Other examples of the more properly formatted "MW_e" and "GW_eyr": [8] [9] — Omegatron 00:25, 19 January 2008 (UTC)

Heh. This document even calls them "subscripts" while writing them on the same line as the text. — Omegatron 00:28, 19 January 2008 (UTC)

As far as I know, what is and is not SI is defined in the official brochure. On page 132 of that brochure it says "the unit symbol should not be used to provide specific information about the quantity" and in the margin it says "For example: The maximum electric potential difference is U_max = 1000 V but not U = 1000 V_max" (emphasis added). In the preface (page 101) it says the "main purpose [of the brochure] is to define and promote the SI" (emphasis added). Unlike some publications, I couldn't find any statement that sentences containing words such as "must" or "shall" are mandatory while sentences containing the word "should" are merely recommendations, so it isn't clear to me if V_max is positively outside of SI or just not recommended. --Gerry Ashton (talk) 01:41, 19 January 2008 (UTC)

The attachment of suffixes, whether or not as a subscript, is not permitted by the (commonly violated) SI rules. I made the changes because the only reliable source I could find used the MWe format. If other reliable sources mention MW_e as preferred then perhaps the article should mention both. Thunderbird2 (talk) 10:38, 19 January 2008 (UTC)

I provided sources right above your comment. — Omegatron 15:10, 19 January 2008 (UTC)

Yes, I didn't mean to suggest otherwise. Those sources are a good start, but they don't prove that MW_e is preferred to MWe. I wondered if there might be an umbrella organisation for the power industry that defines these abbreviations. Any suggestions? Thunderbird2 (talk) 15:35, 19 January 2008 (UTC)

I imagine "MWe" is more common, but MW(e) and MW_e are also used. — Omegatron 23:49, 20 January 2008 (UTC)

IEEE also says that this usage is incorrect:

Attachment of letters to a unit symbol for giving information about the nature of the quantity is incorrect: MWe for "megawatts electrical (power)," kPag for "kilopascals gauge (pressure)," Paa for "pascals absolute (pressure)," and Vac for "volts ac" are not acceptable. If the context is in doubt on any units used, supplementary descriptive phrases should be added to make the meanings clear.

— IEEE Standard Letter Symbols for Units of Measurement

On the other hand, everyone still uses them:

• http://www.google.com/search?q=site%3Aieee.org+MWe
• http://www.google.com/search?q=site%3Aieee.org+MWt+plant
• http://www.google.com/search?q=site%3Aieee.org+MWth
• http://www.google.com/search?q=site%3Aieee.org+VAC

— Omegatron 23:49, 20 January 2008 (UTC)

I think the best solution is to quote the IEEE standard in the article (do you have a more complete reference than just the title?) and then state that the advice is not always followed. Do you agree? Thunderbird2 (talk) 07:17, 21 January 2008 (UTC)

The article already points out that the International Bureau of Weights and Measures considers the symbols incorrect; do you think the IEEE would be better, since that organization is more directly related to electricity? --Gerry Ashton (talk) 07:56, 21 January 2008 (UTC)

As these are not SI units it doesn't seem appropriate to start with BIPM. If they are (as Omegatron argues) IEEE units, my view is that the article should introduce them first in an IEEE context (as subscripted units like MW_e); then go on to say that it is common practice to use suffixes instead (MWe) even though IEEE disaproves (a bit like use by the same industry of kWh in place of kW·h); and end by saying that SI permits neither form. Does that make sense? Thunderbird2 (talk) 08:10, 21 January 2008 (UTC)

I'm not convinced there is one policy toward MW_e and a different policy toward MWe. The IEEE standard indicates MWe is incorrect, but does not suggest MW_e as a replacement, instead it says to use a descriptive phrase. I suspect this is a case of the authors of the IEEE standard and the editors of the IEEE journals not communicating with each other. --Gerry Ashton (talk) 08:33, 21 January 2008 (UTC)

In that case I misunderstood what Omegatron was saying. If your interpretation is correct, that makes IEEE and BIPM consistent with one another (in that neither subscripts or suffixes are permitted). Do you have a copy of the (IEEE) standard? Thunderbird2 (talk) 11:48, 21 January 2008 (UTC)

No, I don't have a copy. It is available for a fee at the IEEE web site. --Gerry Ashton (talk) 22:29, 21 January 2008 (UTC)

I had a look around and discovered I do have a copy. The standard permits some subscripts, but only to disambiguate units that are quantitatively different but share the same name (giving Btu_IT, cal_th and gal_US as examples of this, to distinguish them from Btu₆₀, cal₁₅, gal_Imp). My interpretation is that MW_e is not permitted by this IEEE standard. Thunderbird2 (talk) 23:02, 21 January 2008 (UTC)

A related point is that IEEE explicitly permits use of the abbreviation Wh to mean watt hour, p5:

• "The dot may be omitted in the case of familiar compounds such as watthour (symbol Wh) if confusion is unlikely"

Ah for ampere hour is also mentioned explicitly (p8). Thunderbird2 (talk) 23:12, 21 January 2008 (UTC)

The full document reference is:

IEEE Standards Coordinating Committee 14, IEEE Standard Letter Symbols for Units of Measurement (SI Units, Customary Inch-Pound Units, and Certain Other Units), IEEE Std 260.1-2004 (Revision of IEEE Std 260.1-1993), 24 September 2004.

Thunderbird2 (talk) 23:17, 21 January 2008 (UTC)

Mention of an auto engine in the introduction

The introduction states that an automobile engine produces 25kW when cruising. What automobile? With what engine? At what cruising speed? A boxy van cruising at 70MPH will be using considerably more power maintaining speed than a sleek coupe at 60MPH. Without any details, the sentence is meaningless. 134.121.241.149 (talk) 03:18, 1 April 2008 (UTC)

I think it's an approximation intended to give lay people some idea of the size of output described in terms they can understand, in other words a car produces about 25kW as opposed to an electric fire (about 1kW) or a ship (about 1mW). In this context I would think it does the job without needing to be too precise. Britmax (talk) 13:49, 2 April 2008 (UTC)

Request to add milliwatt and microwatt to article

Milliwatt and microwatt are used in the article Mobile phone radiation and health (and in other places; see Special:WhatLinksHere/Milliwatt and Special:WhatLinksHere/Microwatt). I would like to suggest that these be added to the SI Multiples section. --papageno (talk) 03:08, 2 June 2008 (UTC)

Y These two units have been added to the article. --papageno (talk) 21:40, 17 June 2008 (UTC)

Incorrect use of terms...............

The article makes a few references to "uses" x Watts or "generates" x Watts etc.

The first line actually says "It measures a rate of energy use or production"

Is this strictly correct? A 100 Watt lightbulb doesn't "use" 100 Watts. A 100 Watt generator doesn't "generate" 100 Watts.

A 100 Watt lightbulb "converts" 100 Watts of electricity into 100 Watts of heat and light. A 100 Watt generator converters chemical energy into electricity.

Surely the unit "Watt" isn't the rate of "using" or "generating" energy. It is the rate of "converting" it? —Preceding unsigned comment added by 79.75.13.123 (talk) 13:43, 17 August 2008 (UTC)

Although the processes could be thought of as conversion, the words "use" or "generate" are also appropriate, and easier to understand for people without education in physics. Also, neither lightbulbs nor generators do anything with the remains of James Watt; they use or generate electrical power, which is measured in watts. --Gerry Ashton (talk) 17:13, 17 August 2008 (UTC)

I agree with the previous unsigned comment. Energy doesn't, by any stretch of the imagination, get used or generated. It is converted. And power is the rate of that conversion. To state the energy is used or generated is completely incorrect. I take your point about the capitalisation but feel its rather pointless and trivial. —Preceding unsigned comment added by 86.140.92.253 (talk) 11:18, 30 August 2008 (UTC)

Electrical energy is generated (by conversion of mass or another form of energy of course), and incandescent light bulbs certainly use electrical energy (by converting it to heat + a small amount of light). I don't see a problem with using everyday terms in this way. Dbfirs 18:51, 10 January 2009 (UTC)

Quadrillion

Do we really want ambiguous terms like this in a scientific article? If we want to explain in simple terms, would it not be better to use "thousand million million", or just write out the number? Dbfirs 18:59, 10 January 2009 (UTC)

Is it really ambiguous? Is quadrillion currently used to mean anything other than 10¹⁵? --Gerry Ashton (talk) 19:58, 10 January 2009 (UTC) Corrected 18:30, January 13, 2009.

Long and short scales –OrangeDog (talk • edits) 10:44, 13 January 2009 (UTC)

I was taught (and still use) the fact that a billion is 10¹² (long scale), but I agree that this usage is getting less common. I don't think scientists use quadrillion at all do they? I have just found usages of quadrillion meaning 10¹², 10¹⁵, 10¹⁸ and 10²⁴. It's a bit like "zillion"! - With this amount of confusion, I suggest we just use powers of ten. Dbfirs 11:17, 13 January 2009 (UTC)

"Quadrillion" has to mean 10¹⁵ at least. Also see Quad (energy). Names of large numbers says a long-scale quadrillion is 10²⁴. This difference isn't going to affect the way I balance my checkbook. --Wtshymanski (talk) 14:49, 13 January 2009 (UTC)

Nor my bank balance! The 10¹² was a mistake, but it illustrates that the word means little to most people, and different values to different speakers of English (and not just a difference between American and "Old English" usage - the 10¹⁸ was in Serbia). That's why I think we should avoid using the word in other scientific articles. Dbfirs 08:06, 14 January 2009 (UTC)

I'm reminded of the punchline of the old Newfie joke "Millions? Me son, d'ere's T'OUSANDS!". "Quadrillion" is perfectly well defined - even if the proofreaders at my local newspaper don't instantly recognize the difference, I do, and I'm comfortable with it in appropriate technical context. If we only put in the words that everyone knew, our Wikipedia vocabulary would be ...impoverished? --Wtshymanski (talk) 14:55, 14 January 2009 (UTC)

Supposedly unclear sentence

The IP user 79.86.198.29 altered a sentence to read (addition underlined):

The average power usage by humans (about 15 TW) is commonly measured in these units [Sentence not clear: "by humans" - individuals per day? planet-wide per week?].

Of course, the correct way to ask about what the reader thought was a problem was to edit this talk page, but let's pass over that and discuss the sentence.

Fifteen terrawatts is the same as 15 terrajoules per second. The basic resource that is being used up is energy, which is measured in joules. Power is a rate of using energy, and is measured in watts. As to whether it applies to all humans or per human, I would have thought the overall context of the article would have made it obvious that 15 TW is far too much to be used by one human, but we could adjust the sentence a little if people think it isn't obvious. --Gerry Ashton (talk) 14:41, 23 January 2009 (UTC)

For a non-specialist that wouldn't neccessarily be obvious. Maybe: "On average, the human race consumes energy at a rate of around 15 TW" would be better. --Ralph86 (talk) 19:54, 14 April 2009 (UTC)

Where did this figure come from and does it refer to the energy that humans do or the energy that human-made devices consume? —Preceding unsigned comment added by 134.84.164.186 (talk) 20:29, 27 August 2009 (UTC)

What's a year?

The article says right now

+ Often energy production or consumption is expressed as terawatt hours per year. As one year contains about 8,765.82 hours, one terawatt hour per year equals about 114,08 megawatts.

But the sorts of organizations that report energy in TWh/yr use a civil calendar of 365 or 366 days, giving either 8760 hours or 8784 hours. Better to say "about 114 MW" which is enough significant figures. --Wtshymanski (talk) 14:32, 24 February 2009 (UTC)

This sentence really confused me at first; I didn't get what the unit conversion being done was. I eventually realized it was saying that to *get* a terawatt-hour over a period of one year, it would take being able to *run at* 114.08 megawatts for a period of 1 year. Is there a way to reword the sentence to make that more clear for casual readers like me? Perhaps...

Often energy production or consumption is expressed as terawatt hours per year. As one year contains about 8,765.82 hours, one terawatt hour per year would be the equivalent of providing about 114,08 megawatts of generating capacity for a period of one year.

or...

Often energy production or consumption is expressed as terawatt hours per year. As one year contains about 8,765.82 hours, one terawatt hour per year would be the equivalent of a 114,08 megawatt plant operating at full capacity for one year.

Whatcha think? JorenCombs (talk) 09:36, 20 April 2009 (UTC)

I agree, it is unclear right now. Also the purpose of TW/hrs per year should be explained; like it would be used to show a major energy use's yearly consumption. Like the steel industry uses this many TW/h per year. Note that 114,080 megawatts is 114 Gigawatts, not a paltry 114 MW. So this should be rounded to the nearest MW. 75.170.59.218 (talk) 10:20, 7 May 2009 (UTC)

75.170.59.218, thanks for making the change, but for homwework, please write 10 times:

• "TW/h" is almost always an error. It should almost always be "TW·h".

I have made an appropriate edit to the article. --Jc3s5h (talk) 13:14, 7 May 2009 (UTC)

Thanks guys! Much easier to understand now.JorenCombs (talk) 17:13, 15 May 2009 (UTC)

What's a TWh per year?

Well JorenCombs, it might be clearer to you, but I'm still confused by it.
A TWh is an amount of energy; a TWh/yr is a rate (measured in TW).
So how can "energy production or consumption" be expressed as "terawatt hours per year"? Shouldn't it say: "energy production or consumption" be expressed as "terawatt hours"?

The article currently says "This equates to the continuous energy production of approximately 114 megawatts for the period of one year."
What is the "This" it's referring to? (I'm deducing that "This" is a TWh?) Yes? No? (Help!)

A TWh is 10^12 Wh.
A MWyr is 10^6Wyr = approx 10^6W * 365.25 days * 24 hours = approx 8,800 * 10^6 Wh.
114 MWyr = approx 10^6 * 10^6 Wh = 1 TWh

I have changed the article accordingly. Pdfpdf (talk) 01:23, 15 August 2009 (UTC)

abbreviation

Insofar as it's watt, shouldn't the abbreviation be w? This leaves W for west and tungsten. I note some folk mistakenly writing K to mean a thousand. —Preceding unsigned comment added by 86.148.170.81 (talk) 08:08, 19 April 2009 (UTC)

The CGPM has decided the symbol is "W". Notice the upright type. It is capitalized because it is named after a person, James Watt. The spelled-out unit, "watt", is not capitalized to help distinguish the person from the unit. "West" and "tungsten" are not units of measure and it should be easy to distinguish them from "watt" by context. --Jc3s5h (talk) 15:12, 19 April 2009 (UTC)

(10³)

An IP user insists on inserting "(10³)" into the artilce. I see no reason for this insertion, and in an absense of an explaination here about why this insertion is desireable, I will take the necessary measures to prevent the insertion. --Jc3s5h (talk) 18:44, 26 August 2009 (UTC)

You sent the request for explanation, waited a few hours, then declared there was a absence of explanation and reverted it back. It seems like you are abusing the editing process by doing that. You should be more patient and understanding. The reason why I added it is because it made the article more cohesive. Every other power had a super notation next to it and that is why the thousand watt section should have it too. --IP user —Preceding unsigned comment added by 134.84.164.186 (talk) 17:27, 27 August 2009 (UTC)

I see your reasoning. Another editor has rearranged the article so the powers of 10 are not stated in the running text, but instead are in a table. In the future, please use the edit summary box, below the main editing box, to show the reason for changes. --Jc3s5h (talk) 17:53, 27 August 2009 (UTC)

Yea I saw that. I am figuring out how it looks if it floated to the right so it didn't take so much page space. Thought you could add 'frame' or something to make it float right. Anyways, I forgot to add a suggestion the first time, but didn't think I should go back to add one. I didn't actually notice your first removal, I thought I hadn't refreshed my browser. Lastly, I think your reason for the first removal ("undo; anyone capable of reading this article knows what one thousand is.") is remarkably short-sighted. Some people can understand numbers much better than english words. Regardless I thank you for an introduction to the wiki editing process and I appreciate the time you gave me. —Preceding unsigned comment added by 134.84.164.186 (talk) 19:33, 27 August 2009 (UTC)

Kilowatt again

This sentence: The average annual energy consumption of a household in the United States is about 8,900 kilowatt-hours, equivalent to an average power of about 1 kW.[2] I checked out the site of the ref (I still can't tell where that number on the right comes from). Other than the aec being a bit out of date (it's gone up), I'm having trouble understanding how 8,900 kWh/yr = 1 kW average. Can someone make some sense from this? Thanks 80.101.162.155 (talk)

24 hours * 365 days * 1 kw = 8760 kwh. For those of you paying to use this encyclopedia, you may now request a refund. --Wtshymanski (talk) 17:57, 14 October 2009 (UTC)

woohoo, I get an explanation and a refund! Thanks!! 80.101.162.155 (talk) 19:18, 14 October 2009 (UTC)

I've got to put a hold on this refund program. The artful use of qualifiers like "about" covers us:

8.9 e3 kW·h/yr / (24 h/day * 365.25 days/yr) = 1.0 kW.

—WWoods (talk) 18:04, 23 February 2010 (UTC)

Removed a reference

I removed a reference (http://ebtx.com/mech/ampvolt.htm) as it's nonsense. The volt does not have units of force so the entire discussion on that page is erroneous. 28 Feb 2010

I did look at the page when I saw the deletion and I agree the level of understanding there is not useful to the encyclopedia. It's really helpful when making deletions like this to leave an edit comment saying something like "deleted link to inaccurate analysis page", to avoid the automatic tagging. --Wtshymanski (talk) 04:08, 1 March 2010 (UTC)

200 watts climbing stairs?

I'd like to revise this number down to 125 watts, based on heart rate and relationship to cycling power meteres such as the Saris Powertap. Objections? —Preceding unsigned comment added by 66.230.88.157 (talk) 10:31, 21 February 2010 (UTC)

I think that 125 W is too low. I am 97 kg. Our first floor is about 2.5 m above the ground floor. It take me 5 s to walk up the stairs. Taking g as 9.8 m/s², the work that I do walking up the stairs is 2376 J (mgh). Dividing by the time taken gives 475 W.

If this example is to be kept in place, it needs to be properly verified. Martinvl (talk) 15:34, 21 February 2010 (UTC)

66.230.88.157 has a bizarre indirect way of coming up with the number. Martinvl has a valid approach, but I think 5 seconds is a very fast walking time for that height of stairs. I'd believe 10 s. And body weight makes it seem that 75 kg would be closer to average. From those we'd get 184 W. That's close to the 200 W in the article. But the 10 s is my OR, as is Martinvl's 5 s, so we'd need a better way to get that data. Ccrrccrr (talk) 20:23, 27 February 2010 (UTC)

How is it "bizarre"? Human beings producing work have a direct relationship between heart rate and work performed. If I can climb 400 stairs at a STEADY heart rate of 130bpm, then later get on a device that directly measures power output in watts and produce 150W at a heart rate of 130bpm, that seems to be a pretty direct relationship to me. Thoughts? Doing it mathematically with gravity largely ignores the biomechanics, I think. —Preceding unsigned comment added by 66.230.83.127 (talk) 20:01, 6 March 2010 (UTC)

That's backwards. Doing it from heart rate ignores the biomechanics. You say, "Human beings producing work have a direct relationship between heart rate and work performed." But that's not true. For example sleeping vs. doing isometric exercise you will have a different heart rate, but in both cases be doing zero mechanical work. Ccrrccrr (talk) 22:48, 7 March 2010 (UTC)

Let's see. A 75 kg human climbing 3 metres in 10 seconds is doing work (above and beyond keeping alive) at a rate of 75 * 9.81 * 3 /10 = 220 and change watts. Do we want to give an order of magnitude or must we give spurious precision? Never mind the heart rate, the point is meant to illustrate how big a watt is, not meant as a Wikipedia side-track dissertation on biomechanics. I've not the slightest interest in finding references for "A human being weighs about 75 kg", "Gravity is about 9.81 m/s/s", "A flight of stairs is 3 metres high" or "One climbs a flight of stairs in 10 seconds", or any combination of these factors, which will be the only way of subduing the Wikicritics. --Wtshymanski (talk) 00:21, 8 March 2010 (UTC)

In the Example is laso said that the laborer produces during 8 hours working day a total of 75 watts. Obviously it should by 75 kilowatts.Ninoak (talk) 07:32, 22 May 2011 (UTC)

No, 75 kilowatts is about 100 horsepower. Jc3s5h (talk) 12:53, 22 May 2011 (UTC)

User:Ninoak's wording suggests that he/she confused watts and joules. A device only produces a total output of watts if the device has many separate power production components that can run in parallel - for example a power station with ten generators. If the numer of watts is totlled over time, then the result is joules (one joule = one watt x one second). Martinvl (talk) 06:20, 23 May 2011 (UTC)

Car engines

I downgraded a previous editor's estimate of the power of a "typical passenger car" by clarifying "medium-sized". I used List_of_Volkswagen_Group_petrol_engines as my point of reference. Perhaps the previous editor was quoting the power of teh car that he woudl like to own rather than the car that he does own, or maybe AMerican cars are just more powerful (and use more fuel) than European cars. Even a 2 litre turbo BMW only produces 150 kW. Martinvl (talk) 20:24, 27 April 2010 (UTC)

Power

Power is the product of force and speed. It takes a bigger motor to raise an elevator at 5 metre/second than at 1 metre/second. We should be consistent with the defintion of power when defining the watt. A joule/second is a newton-metre/second, or in other words, 1 newton moving something at a speed of 1 metre/second. --Wtshymanski (talk) 14:23, 3 August 2011 (UTC)

For example, just looking at stuff I can find for free on Google Books and since my physics textbook is at home: pg 44 of Applied dimensional analysis and modeling by Thomas Szirtes and P. Rózsa says 1 watt is exactly 1 newton times (1) metre per second. There would be others. --Wtshymanski (talk) 14:35, 3 August 2011 (UTC)

The above is correct elementary high-school physics. Ccrrccrr (talk) 16:18, 3 August 2011 (UTC)

Oh, this was never about the physics, really. --Wtshymanski (talk) 18:11, 3 August 2011 (UTC)

Link to Parkers Car Guide

I made the note that the power of a medium-sized family car lies between 50 kW and 250 kW. I have twice had to revoke a change when somebody has replaced the 50 kW with 150 kW. I don't know about American cars, but in Europe 50 kW is a fairly small car - I have recently bought a 63 kW car (four seater, four doors, 1.2 L engine, suits a retired couple or a young married couple with oneor two small children). In Europe, a car with a 150 kW engine is certainly towards the higher end of "family cars". I added the link to Parkers so that I have a reference against which to back my claims. For the record, Parkers is one of the most reputable lists of car prices in the UK. Martinvl (talk) 16:22, 10 August 2011 (UTC)

Spelling of symbols

I note that symbols up to "kW" are spelled with a small first letter in the article, while those from "MW" up have a capital letter in first place.

Is there any reason that makes sense for this inconsistency? — Preceding unsigned comment added by 133.2.9.40 (talk) 23:08, 21 August 2011 (UTC)

I believe the prefixes for multipliers less than 1,000 were created earlier (by the General Conference on Weights and Measures) than the larger multipliers. Jc3s5h (talk) 23:59, 21 August 2011 (UTC)

UK & US household consumption

Given that US households use about twice the energy of a UK house, I thin it appropriate that both be included. The wording is perhaps a little POV, so I will change that, but keep both figures in place. Martinvl (talk) 08:49, 11 November 2011 (UTC)

I believe you are being inconsiderate of the reader. The point of the paragraph is to show that annual energy consumption is actually a unit of power, not a unit of energy, and also, to give an order-of-magnitude concept of how much a kilowatt is. The consumption of an average US household is merely a convenient example. Trying to stick in the power consumption of your favorite country is off-topic and distracting to the reader. There is no cause to insert the average household power consumption of more than one country in this section. Remember, this article is not about household power consumption around the world. Jc3s5h (talk) 13:17, 11 November 2011 (UTC)

I only came to this in providing a reference for what looked like a guestimate figure for UK consumption - the reference to the UK consumption was already an established part of the paragraph. If the US figure is to stay then I would strongly support the inclusion of the UK figure . Taking a global view , the USA figure is an extreme and yet it appears to be presented as a norm. I suggest that either we ensure the US figure is presented as the most profligate use of energy or it is balanced by a least one figure from a developed country with a more moderate use of energy.  Velella  ^{Velella Talk}   13:35, 11 November 2011 (UTC)

If someone knows an average figure for developed countries, or can demonstrate that a particular country is in the middle of the range of developed countries, I would prefer to see such a figure replace the US figure. Jc3s5h (talk) 13:45, 11 November 2011 (UTC)

I would prefer to remove all references to average household electricity consumption - after all we are trying to give the reader a "feel" for what a kilowatt is - IMO, many people have no feel for how much electricty their house is consuming - do you have air conditioning? Do you use electrical heating? They would rather be told that they are using the equivalent of four single-bar heaters than the other way round. Martinvl (talk) 20:47, 11 November 2011 (UTC)

Include Yottawatt

Yottawatt redirects here but there's no subtitle of it. Perhaps someone can write a paragraph on it? thx 71.197.67.191 (talk) 04:03, 1 February 2012 (UTC)

Add a time-measure in Examples?

"A laborer over the course of an 8-hour day can sustain an average output of about 75 watts; higher power levels can be achieved for short intervals and by athletes."

=> 75 watts on an 8-hour day is quite low, especially if you compare it with the first example in 'Examples': "A person having a mass of 100 kilograms who climbs a 3 meter high ladder in 5 seconds is doing work at a rate of about 600 watts." Someone either forgot to add a measure of time, e.g. "A laborer over the course of an 8-hour day can sustain an average output of about 75 watts per half-hour", or the number 75 must be substituted by a more realistic value. 134.58.253.57 (talk) 19:33, 22 March 2012 (UTC)

No. It's about right as it stands. Andy Dingley (talk) 19:41, 22 March 2012 (UTC)

"75 watts per half-hour" is meaningless. Perhaps 134.58.253.57 would understand better if we pointed out that the worker who outputs 75 watts on average for an 8 hour day outputs 75 W ⋅ 8 h ⋅ (60 min/h) ⋅ (60 s/min) = 2,160,000 joules. Jc3s5h (talk) 19:50, 22 March 2012 (UTC)

Flux Capacitor operating power

I protest the removal of information regarding the operating power of the Flux Capacitor. The information was factual and properly referenced. — Preceding unsigned comment added by 65.190.69.83 (talk) 22:37, 20 October 2012 (UTC)

Since the Flux Capacitor is entirely fictitious, I disagree with your use of "factual" - not only is the information wildly irrelevant, but due to the imaginary nature of the component in question, it utterly fails to give the reader any sort of information as to the scale of the unit whatsoever. 80.156.44.33 (talk) 13:18, 14 December 2012 (UTC)

"EKG" link

The link "EKG" under the Microwatts heading links to a Polish pop album. I am somewhat sceptical that this was the destination that the author intended for said link. 80.156.44.33 (talk) 13:20, 14 December 2012 (UTC)

sSorted - EKG is the German abbreviation for electrocardiogram. Martinvl (talk) 13:58, 14 December 2012 (UTC)

Kilowatt section missing rate

The last sentence there says "A surface area of one square meter on Earth receives typically one kilowatt of sunlight from the sun (on a clear day at mid day)." Shouldn't that have some sort of rate? 50.88.78.102 (talk) 01:38, 5 January 2014 (UTC)

A watt is a rate, 1 joule per second. So the square meter described above receives 1000 joules of energy per second. Jc3s5h (talk) 02:42, 5 January 2014 (UTC)

Ws or Joule is a unit used in photography to describe the energy stored in the capacitors of the flash circuit.

The article incorrectly states the Watt second is used in photography as the energy stored in the flash tubes. It is actually stored in capacitors in the power pack portion of the system. The flash tube is also rated in Watt seconds, not as a unit of storage, but as a specification of the maximum energy it can handle without damage. The flash tube provides a place for the energy stored in the capacitors to be converted to energy as light, or lumens.

69.174.58.148 (talk) 18:54, 15 July 2014 (UTC) Photographer EE, July 15, 2014

No, the article indicates the watt-second is used as a unit to express the energy storage in flash lamps, not flash tubes. It is also linked to the "Flash (photography)" article, which describes photographic flash units as entire devices, and does not delve into the component parts of a photographic flash unit. Thus I think the article is acceptable. Jc3s5h (talk) 19:23, 15 July 2014 (UTC)

Table instead of text

I think the various examples of multiples or orders of magnitude should be merged with the table. IMO, as it is, the examples are wordy and tedious.CountMacula (talk) 19:11, 6 November 2014 (UTC)

Bad Example

The following is a terrible example of 600 watts "A person having a mass of 100 kilograms who climbs a 3-meter-high ladder in 5 seconds is doing work at a rate of about 600 watts. Mass times acceleration due to gravity times height divided by the time it takes to lift the object to the given height gives the rate of doing work or power.[notes 1]" A 100kg person weighs 220 lbs, a 3 meter ladder is 9 feet. Very few people that are 220lbs know what it feels like to climb a 9ft ladder in 5 seconds. that is almost Olympian.Ccubedd (talk) 17:26, 20 February 2014 (UTC)

Do you only know overweight 220 lb people? I'm healthy around that weight, and I don't think it's too crazy to climb 9 feet in 5 seconds, assuming you have a ladder that's much longer than 9 feet so that the movement doesn't involve getting on/off, and assuming that the rungs are at least a foot apart. A brisk climb, maybe, but olympian is pushing it.71.245.236.232 (talk) 09:30, 23 March 2015 (UTC)

It certainly is possible. Human-powered transport says up to 2500 watts for "Elite track sprint cyclists" so 600 watts is not "almost Olympian". I don't find it a useful example myself but I suppose some people would. Kendall-K1 (talk) 10:24, 23 March 2015 (UTC)

Apparent power

This article says that current times voltage equals watts, which is only true for a resistive circuit (or a load with perfect power factor correction) if alternating current is supplied, as it is for direct current.. If a component is an induction motor, it will have a power factor less than unity, and the watts will be less than this equation states. Edison (talk) 03:46, 5 January 2016 (UTC)

It's correct and reasonable as it stands, even though it's not complete. Perhaps a section (mostly an onward link) on power factor should be added after it.

We should NOT explain power factors embedded within the first introduction of the electrical Watt. Especially not with parentheses, as they destroy readability. Andy Dingley (talk) 14:43, 5 January 2016 (UTC)

As Andy said, it's true as it stands. There is only a problem if one assumes that one may separately measure average current with one meter, average voltage with a different meter, and blindly multiply the two quantities to obtain power. If instead one uses instruments that give instantaneous current and voltage at a certain instant, and multiplies those quantities, one will obtain the true instantaneous power. Jc3s5h (talk) 00:30, 6 January 2016 (UTC)

This article at present gives the formula for apparent power and says that it equals power. RMS AC voltage, accurately measured, times RMS AC current, accurately measured, does not, in most cases, save for purely resistive loads, equal watts consumed by a load. Anyone asserting AC watts equals volts times amps would fail a high school physics course. The article, as it stands, is at best misleading, since it only applies to resistive loads. Practical meters (say a Fluke RMS meter) do not measure instantaneous volts and amps: RMS implies measurement over a period of time. At least guide the reader to coverage of power factor, It is not just a frill, a technicality, an exception, or a special case. For many real-world loads, the apparent power is significantly higher than true power. Edison (talk) 02:14, 6 January 2016 (UTC)

AC power isn't part of high school physics in my country, and I doubt if it is in the creationist US either. Nor is this even a high school physics course, it's an encyclopedia that has to expect readers at every level. Our results are judged by how well we communicate useful knowledge, not by how precisely accurate the texts are when that compromises readability. Too many exceptional cases early on are just the way that we lose more readability than we gain accuracy. Andy Dingley (talk) 02:45, 6 January 2016 (UTC)

The article is correct and not misleading. If you're talking about "W = V × A" that's always instantaneously true even in an AC circuit. It only becomes untrue after you stop talking about instantaneous conditions and introduce RMS, phase, impedance, and vectors. This article does not mention Fluke meters or RMS measurements. Kendall-K1 (talk)

It is not "useful knowledge" to mislead readers by stating that volt-amps are identical to watts. The fact that measured volts times measured amps overstates watts for most AC loads is not an "exceptional case." A large difference is quite common. The article does not limit the misleading equation to "instantaneous" quantities, so I would welcome the addition of that qualification. If "AC power isn't part of high school physics in my country" that is regrettable. Edison (talk) 03:21, 6 January 2016 (UTC)

We should at least achieve the level of accuracy in "Physics for Nonphysicists" which explains that current times voltage is apparent power, and is only equal to true power for DC or in a purely resistive circuit. We should direct the reader to the apparent power article for further explanation.An alternative would be to restrict the discussion or examples to resistive circuits.Edison (talk) 03:48, 6 January 2016 (UTC)

"restrict the discussion or examples to resistive circuits"

This article is on watts, not even just electrical power. The initial scope here begins with horses, their replacement with steam engines, and the recognition of power as a measurable concept allowing the comparison of machines on their basis of "ability to do work". We start from a level that's very broad and very introductory. We will have readers who don't even comprehend what AC power is, certainly not ideas like a phase lag between current and voltage.

Obviously we need to link forward to power factor and apparent power, but we must still do that in a way that doesn't compromise explanation of simple DC resistive power. Parentheses and convoluted nested clauses are anathema to that. Andy Dingley (talk) 10:19, 6 January 2016 (UTC)

I suggest that the "V x I=W" overly simplified statement would be improved by adding that that is only true for purely resistive circuits, and that for circuits containing capacitors or inductors there are more complex considerations. No parentheses are required to offer more information in a different article via a suitable wikilink. Edison (talk) 23:50, 6 January 2016 (UTC)

Capitalization in table

I fat-fingered the explanation I was typing during my revert, so I will explain fully here. It's OK to capitalize watt when it's the first word in a sentence, sentence fragment, or table entry. It's no different from mile, dog, pencil, train or any other common noun. Indefatigable (talk) 17:55, 9 January 2017 (UTC)

I see this is being discussed at Template talk:Infobox unit Indefatigable (talk) 18:11, 9 January 2017 (UTC)

It could be capitalized, since could be thought of as a title for the infobox. But it could also be lower-case, as in a dictionary entry. Please see Template talk:Infobox unit#RfC: capitalization rule for name parameter. Jc3s5h (talk) 18:14, 9 January 2017 (UTC)

Light bulbs

I wonder if it's time to do away with the light bulb comparisons. You can't buy a 100 watt light bulb any more, so some time soon young people reading this article won't know what we're talking about. Worse, at least in the US, light bulbs are starting to appear on the shelves that are marked "100 watts" when they actually only consume 12 or so watts. Kendall-K1 (talk) 22:14, 12 June 2017 (UTC)

Confusion section

I'm going to revert the change to the Confusion section header. We don't need to explain the confusion in the header, that's what the rest of the section is for. Adding words to it makes it more confusing (as a header), not less. Kendall-K1 (talk) 02:47, 22 June 2017 (UTC)

Request to add KWh_e and KWh_h

The terms are used in CHP to define the generators output in heat and electricity. User:ralph86 14 apr 2009

Section on confusion between watts, watt hours etc

I made some changes to this section last week, and I see that these didn't all go over well, so I'm making a second attempt; I hope these changes make the thing clearer. Typing on my phone so apologies if this is terse. Andrew Gradman ^talk/_WP:Hornbook 10:13, 28 June 2017 (UTC)

Sorry, but I don't see this as a useful change. What is the problem with watt/hr (watts per hour)? Why do we need to mention that at all? (It's not mentioned in the supposed ref) - so why move this misleading "watts per hour" to the top and strip out watt.hours, which are an important unit? Andy Dingley (talk) 10:57, 28 June 2017 (UTC)

I don't like the phrase "rate per unit time". A rate by definition is a change over time. And "It should not be confused" is WP:EDITORIALIZING. Kendall-K1 (talk) 04:17, 29 June 2017 (UTC)

Needs edit/clarification

"A surface area of one square meter on Earth receives typically about one kilowatt of sunlight from the sun" - over what period of time? — Preceding unsigned comment added by 89.197.134.148 (talk) 10:30, 23 November 2017 (UTC)

Please reread the article and references until you realize why this question makes no sense. Jc3s5h (talk) 16:34, 23 November 2017 (UTC)

First sentence

I'm not happy about this as the first sentence: "The watt (symbol: W) is a unit of electrical and mechanical power." While true, it seems to limit the watt to only measuring electrical and mechanical power. Kendall-K1 (talk) 02:37, 25 December 2017 (UTC)

Light bulbs

@Kbrose: I earlier proposed removing the light bulb examples. No one objected, so I went ahead and removed them. Since apparently there is an objection, I'm going to re-state here what I said earlier:

I wonder if it's time to do away with the light bulb comparisons. You can't buy a 100 watt light bulb any more, so some time soon young people reading this article won't know what we're talking about. Worse, at least in the US, light bulbs are starting to appear on the shelves that are marked "100 watts" when they actually only consume 12 or so watts. Kendall-K1 (talk) 03:05, 16 January 2018 (UTC)

Outrageous. They should use something people have an intuitive grasp of, like horsepower. EEng 04:07, 16 January 2018 (UTC)

If my hardware store sold "⁠1/100⁠ hp" light bulbs I would buy them. Actually I think they might still use "candlepower" in some cases. Kendall-K1 (talk) 04:44, 16 January 2018 (UTC)

You can buy 75W CFLs, in ES mounts. They're a super-life grade from Philips, intended mostly for places where the cost of fitting a replacement is far greater than the lamp cost, such as big stairwells and atria. I've also recently bought a load of 50W and 100W LEDs, but they're wire-in, not lampholder-fit. Andy Dingley (talk) 11:16, 16 January 2018 (UTC)

I don't know about elsewhere, but in the UK there is always a comparison against incandescent, for example a halogen much say '70 w = 92 w'. People generally think in watts, rather than lumens, etc. –Sb2001 10:58, 22 January 2018 (UTC)

Exactly. If I search on Amazon for a "60 watt light bulb" the first five results consume 10.5, 43, 8.5, 75, and 8.5 watts. And most of them say "60w" or even "60-watt" on the label. Kendall-K1 (talk) 15:18, 22 January 2018 (UTC)

Light bulbs are (used to be???) a great example to use when describing electricity use, mainly because (1) a bulb always use electricity at a constant rate (e.g. 60 W), and (2) everyone is aware of the power rating on the bulb, so that they can attempt to get the correct bulb to replace it when it breaks, and (3) everyone can identify with the fact that some use electricity faster than others (e.g. a 50 watt bulb uses energy at half the rate of a 100 W bulb). But since bulbs no longer have an easy link of watts vs brightness due to changes in the technology used, we should try to discover another easy, clear example to use. (I can't think of one off the top of my head). If a better example does exists, then we should use it. If not, then I don't think it is a big deal to continue using the light bulb example, perhaps with different (lower) watt ratings. Carlroddam (talk) 07:08, 23 January 2018 (UTC)