1. Perpetual motion machines of the second kind are not allowed by the (briefly
ID: 1291693 • Letter: 1
Question
1. Perpetual motion machines of the second kind are not allowed by the (briefly explain)
a. First Law of Thermodynamics b. Second Law of Thermodynamics
c. equals the entropy increase d. cannot be completely converted to work
2. According to the second law of thermodynamics, which of the following applies to the heat received from a high temperature reservoir by a heat engine operating in a complete cycle? (briefly explain)
a. must be completely converted to work b. equals the entropy increase
c. converted completely into internal energy d. cannot be completely converted to work
3. The maximum theoretical thermodynamic efficiency of a heat engine operating between hot and cold reservoirs is a function of which of the following? (briefly explain)
a. hot reservoir temperature only b. cold reservoir temperature only
c. both hot and cold reservoir temperatures d. None of the above choices are valid
4. Which of the following choices best corresponds to what is required by the second law of thermodynamics for any process taking place in an isolated system? (briefly explain)
a. entropy decreases b. entropy remains constant
c. entropy increases d. entropy equals work done on the system
Explanation / Answer
1.
Perpetual motion is motion that continues indefinitely without any external source of energy.[2] This is impossible in practice because offriction and other sources of energy loss.[3][4][5] A perpetual motion machine is a hypothetical machine that can do work indefinitely without an energy source. This kind of machine is impossible, as it would violate the first or second law of thermodynamics.[4][5][6]
Cases of apparent perpetual motion can exist in nature, but such motions either are not truly perpetual or cannot be used to do work without changing the nature of the motion (as occurs in energy harvesting).[7] For example, the motion or rotation of celestial bodies such as planets may appear perpetual, but are actually subjected to many forces such as solar winds, interstellar medium resistance,gravitation, thermal radiation and electro-magnetic radiation
2 : d
The second law is a statement that all processes go only in one direction, which is the direction of greater and greater degradation of energy, in other words, to a state of higher and higher entropy. For example, when we stir a cup of tea, the smooth and swirling motion that we make with a spoon soon disappears. The swirling motion is converted - from conservation of energy - into a very tiny increase in the temperature of the tea. However, no matter how long we wait, the still tea in the cup will never suddenly start to swirl accompanied by a tiny drop in its temperature. Similarly, if a glass shatters, no amount of waiting will ever see the glass suddenly re-assemble itself, although the glass in tact and the shattered glass, upto some minute differences, have the same energy. There are endless similar examples from daily life that one can quote. Since in all the examples, energy and momentum are conserved, clearly it is not these considerations that are responsible for events in time not being able to reverse themselves. The question is the following: why are certain physical phenomenon, allowed by conservation laws such as energy, nevertheless forbidden from occurring? The second law of thermodyamics is the underlying reason that unlikely events do not occur. Entropy is a measure of the likelihood for some event to occur, and only those events can occur for which entropy increases, since they are more likely. In other words, an isolated system always goes from a less probable to a more probable configuration.
3 : c
4 : c
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