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July 5, 2015

Homework Help: physics-please check

Posted by Emma on Monday, May 14, 2007 at 4:46am.

is this right?:

when a form of energy changes from one form to another some energy may transfrm into a useful form, those useful form of energy is high grade energy.while the rest of the energy will always change to form we cannot use.which is called the low grade energy.

if i am not right, can you please correct me?or is there any other things that i can add to about what is low grade and high grade energy?


There are not simply two grades of energy, high and low. There is a quantity called entropy, designated by S, and a quantity called available energy, and defined as H - TS. The quantity S increases or stays the same in all reactions involving closed systems, so that the available energy decreases or stays the same.

What you are trying to state is the second law of thermodynamics, which involves the tendency of entropy to increase, as available energy is degraded to heat. Heat (thermal energy) is not 100% available and is therefore of "low quality".

so what is high grade energy?

Energy that is 100% available to perform work. Potential energy and electrical energy are two examples.

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