A watts question.

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perfectbite
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A watts question.

Post by perfectbite » Thu Aug 26, 2004 10:28 am

In researching watts I found one web page that refferred to watts as energy and another that referred to watts as power. Maybe on page 5 of section 7 subparagraph 3a. under Miscellaneous a distinction was given as to applications but I didn't read that far. <p>I have come across instantaneous watts, watt/seconds/minutes/hours and have two questions, if anyone knows the answers off hand. <p>1. For a 100 watt light bulb or 1100 watt hair dryer, what wattage per time value is that number referring to? Wh, Wm, Ws. ? What time value assumptions are being omitted by the manufacturers in the giving of that information? Would there be a difference between residential and industrial/institutional watts labelling?<p>and <p>2. If a wattage is given in instantaneous watts how is that instantaneous value converted into longer time periods? i.e. 100 watts instantaneous would be how many watts per s/m/h?<p>
Thank You.<p>[ August 26, 2004: Message edited by: perfectbite ]</p>

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Dave Dixon
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Re: A watts question.

Post by Dave Dixon » Thu Aug 26, 2004 11:09 am

I'm pretty confident of this answer, but expect more input from others here...
Wattage is a unit of power. It can be determined by measuring Voltage and Current. Watts = Volts X Amps. Or measure Resistance and Current. Then
Watts = (Amps squared) X Ohms.
If you burn a one hundred Watt lightbulb for one hour, you have consumed 100 Watt/Hours of energy.
I consider the Watt/Hour to be a unit of energy, rather than of power.
Standing by for criticism!!!
Dave

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Chris Smith
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Re: A watts question.

Post by Chris Smith » Thu Aug 26, 2004 1:36 pm

A watt is a quantifiable amount of electrons.<p>Starting with the amp, you add in time which is one of its measurements, and pressure which is voltage, and the quantity equals a given number of electrons. <p>The number is one amp = 6,250,000,000,000,000,000 electrons per second.... times volts = one watt/second

cato
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Re: A watts question.

Post by cato » Thu Aug 26, 2004 2:00 pm

The SI unit of power, one joule per second, is called a watt. A joule is a unit of energy.<p>When you buy energy from the power company you are charged by the kilowatt-hour:<p>1KWh=1000W X 3600 sec = 3600000 Watt-second = 3600000 Joules

rosborne
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Re: A watts question.

Post by rosborne » Thu Aug 26, 2004 2:20 pm

I think of watts as Power and joules and energy. One interesting conversion is
1 horsepower = 746 Watts = 550 ft*lbs/sec.
A watt can be thought of as energy spent over time which makes the watt-hour confusing, for me anyway.
Serway says, "Power is defined as the time rate of energy transfer."
1 watt = 1 joule per second, literally one joule of energy over one second to accomplish one watt of energy transfer.
Since watt*hours is (joules/sec)*hours and there are 60 seconds in an hour
1 watt*hour = 1(joules/sec)*hours*(60*seconds/hours) = 60 joules;
watt*hours and kilowatthours(60,000 joules) are energy by definition.
Instantaneous Power is the dot product of a Force vector and a velocity vector which is a fancy way of saying if you want to move something, even if that something is a tiny little electron, you have to expend energy over time to move it and the result is that you have committed the high crime and misdemeanor of doing work (which is an obscure physics term that has almost no relationship to the english word upon which it is based :) ), furthermore the energy you expended is added to the object you tried to move according to the work energy theorum. <p>Nowadays, thanks to marketing and people with Master of Business Arts degrees, we add value to a project, not work. Value is undefined in the physical world, which is why nothing *works* the way it should.

rosborne
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Re: A watts question.

Post by rosborne » Thu Aug 26, 2004 2:28 pm

Should be 'joules as energy' not 'joules and energy'.

toejam
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Re: A watts question.

Post by toejam » Sat Aug 28, 2004 1:22 pm

What's a watt? A watt a measured amount of work.You can read them on the wattmeter on your home. A horse can lift 550 pounds one foot in a second and if it applies that amount of effort attached in an efficient generator he will be able to light about ten 75 watt light bulbs till he stops. The average man generates 1/5 of a horsepower. I'm talking about sustained working times, not peak output.

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