This set of Physics Multiple Choice Questions & Answers (MCQs) focuses on “Second Law of Thermodynamics”.
1. A process is carried out between 2 systems. It is possible for entropy of one system to decrease. True or False?
Explanation: The net entropy change has to be positive. It is possible for the entropy of a system to decrease, but the entropy of the second system should increase enough to ensure net entropy increases.
2. According to the first law of thermodynamics, a book lying on a table can fly upwards on its own by using the internal energy of the table. True or False?
Explanation: In the above said process, energy is conserved and according to first law, this is valid. It only violates the second law. So, the given statement is true.
3. Which law of thermodynamics says that efficiency of a heat engine cannot be 1?
Explanation: The second law of thermodynamics fundamentally disallows many processes that may be consistent with the law of conservation of energy. It says that entropy change in an irreversible process has to be positive. This means that heat given to an engine can’t all be converted into work. Therefore, efficiency cannot be 1.
4. Which of the following is the Kelvin Planck statement?
a) Heat from a cold reservoir cannot be transferred to a hot reservoir without external work
b) Efficiency for a reversible cyclic process can be 1
c) Heat from a hot reservoir can be completely converted into work if process is reversible
d) Efficiency of a heat engine is less than 1
Explanation: Kelvin Planck statement is: No process is possible whose sole result is the absorption of heat from a reservoir and complete conversion of that heat into work. So, this implies that efficiency of a heat engine is less than 1.
5. The second law of thermodynamics states that?
a) Entropy of an isolated system can never decrease over time
b) Entropy of a pure crystalline substance at 0K is 0
c) Energy is conserved
d) Entropy of a system can never decrease
Explanation: The second law states that entropy of an isolated system can never decrease over time. There can be a system whose entropy decreases, but, at the same time in that process another system’s increase in entropy will more than compensate for that decrease.
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