I've a rather theoretical question: Is there a relation between cpu/core usage and the energy consumption. 
I try to explain it in an example:
Lets say we have a set of tasks T and one core C1. C1 would complete the set T within 10 seconds while having a usage of 100%. Can it be more energy efficient to use two cores C1 and C2 and divide the tasks from T among them so it is still finished in 10 seconds but the usage of C1 and C2 during this time is 50%? (<-- just an example, the numbers are not real)
Like a car has a certain speed where it does not waste to much gas (even though i am aware that a vehicles speed is more equivalet to a cores frequency). 
I although thought that when a cpu/core runs on 100% it gets warm than (lets say) 50%, which means it needs more energy for cooling.

I would be thankful for any comments on this topic

cheers