Watt

TSN79

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...

russ_watters

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

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

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?