THE INTERNET PLASMA PHYSICS EDUCATION EXPERIENCE  

Stored Energy CalculationMore Explanation... This page will show you How to figure out the temperature increase equation by Canceling UnitsQUESTION: How hot will 2 cups of water get from 2 minutes in a microwave oven? Joules Specific Heat of Water = 4180  Kg  Deg. C Power of Microwave = 750 Watts Joule Watt =  Second Weight of Water = 0.454 Kg Time of Heating = 120 Seconds You want to write an equation so the units cancel and you are left with degrees C. The Specific Heat of Water has Deg. C in the denominator, so we will have to divide by it. Kg  Deg. C X Deg. C = something *  4180 Joules"X" will be the increase in temperature (in degrees Celsius) we expect to see from applying the facts above. "something" has to have Kg in the denominator, so: Kg  Deg. C 1 X Deg. C = something else *  *  4180 Joules 0.454 KgNow we need to cancel Joules, so let's multiply by what a watt is: Kg  Deg. C 1 Joule/second X Deg. C = another thing *  *  *  4180 Joules 0.454 Kg WattAnother way to write that is: Kg  Deg. C 1 Joule X Deg. C = another thing *  *  *  4180 Joules 0.454 Kg Watt*secondJoules and Kg cancel out; now let's get rid of Watts and seconds in the next step: Kg  Deg. C 1 Joule X Deg. C =  *  *  * 750 Watts * 120 Seconds 4180 Joules 0.454 Kg Watt*secondAll the units now cancel on the right hand side of the equation (whew!) leaving Degrees Celsius. So the answer is : 750 * 120 / 4180 / 0.454 = 47.425 Degrees Celsius increase in temperature! In the real world, "your mileage may vary." Try and think why that could be. 

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