explaining the concept of Watt to me


by TSN79
Tags: concept, explaining, watt
TSN79
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#1
Nov21-05, 04:25 PM
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A guy was explaining the concept of Watt to me, using a drawing of a machine that used 1 Joule per second, i.e. an oven. This one watt is now converted into heat, but excactly how much heat does 1 watt equal in terms of temperature? I'm not even sure if there is a relation, but if not, how is an oven of let's say 2 kW supposed to tell me anything of use?

Someone also told me that explaining this would require me to know the concept of enthalpy...anyone...
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russ_watters
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Nov21-05, 05:25 PM
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4.19 Joules = 1 Calorie = the amount of heat required to raise 1g (1mL) of water 1C.

So lets say a 1500W microwave oven is 50% efficient and you want to boil 1L of 20C water...

1000mL*80C*4.19=335,200J

335,200J/750J/s=447s=7.45 minutes
mezarashi
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Nov21-05, 09:17 PM
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Quote Quote by TSN79
how much heat does 1 watt equal in terms of temperature? I'm not even sure if there is a relation, but if not, how is an oven of let's say 2 kW supposed to tell me anything of use?
Nope. It doesn't tell you much without knowing where that 2kJ per second is going. Heat is related to temperature by the calorimetric equation

Q = mCT

where Q is the heat exchanged, m is the mass, C is the specific heat constant of the substance and T is the temperature change. So depending on what you're heating with that 2kW, you will end up with different temperature changes (e.g. it's easier to 1 gallon of air than 1 gallon of water).

On another note, the 2kW does tell you something: how much you will be needing to pay on your electric bill ;)

krab
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Nov21-05, 10:15 PM
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explaining the concept of Watt to me


Quote Quote by TSN79
but excactly how much heat does 1 watt equal in terms of temperature?
Yes, you are confused. 1watt is not an amount of heat; it is a rate of heat flow. It's like you are asking: 40mph is how long a distance?


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