Complexity Explorer Santa Fe Institute

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Introduction to Information Theory

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2.2 Entropy » Quiz Solutions

The following questions are in reference to the video: Information.2.2.Entropy.


Question 1: Let us investigate the choices to the question:

Entropy was proposed to explain why heat energy cannot be fully converted to work in an engine.
Entropy measures the amount of disorder in the microscopic states of a physical system. The Second Law of Thermodynamics states that the entropy cannot decrease. If all heat energy were converted to work, then the entropy would decrease. Thus, entropy (and specifically the Second Law of Thermodynamics) explain why heat cannot be fully converted to work. Video explanation

Question 2:

We know that the heat energy in a gas is stored in the movements of the molecules, with faster molecules having more energy.  If the gas does work in an engine by pushing against a piston, some of this energy is converted into work and it must be that the molecules slow down.  So the correct answer must be either the first or the second answer.
However, by the Second Law of Thermodynamics, we know that it is not possible for the degree of disorder, as measured by the entropy, to decrease.
Thus, the correct answer is C: "The molecules slow down, but their degree of disorder is unchanged or increased”.

Question 3: 

The Second Law of Thermodynamics states that entropy, a measure of disorder, can never decrease.