Explanation:
Efficiency is defined as the ratio between the useful output over the total amount consumed. 
The fan does 500W of useful work while wasting 300 W. The total power consumption is 800 W (500 + 300).
Potential energy which is the stored energy an object has waiting to be used
<span>In an internal combustion engine, heat flow into a gas causes it to expand.
The application of direct force to specific parts of the engine will produce </span>expansion of the high-temperature<span> and high-</span>pressure<span> gases. Which will transform the chemical energy from the fuel (such as gasoline or oi) into mechanical energy.</span>