Why can't the efficiency of a heat engine ever be $100 \%$?
(N/A) The efficiency of a heat engine is defined as $\eta = 1 - \frac{Q_2}{Q_1}$,where $Q_1$ is the heat absorbed from the source and $Q_2$ is the heat rejected to the sink.
According to the Second Law of Thermodynamics (Kelvin-Planck statement),it is impossible to construct a device that operates in a cycle and produces no effect other than the extraction of heat from a single reservoir and the performance of an equivalent amount of work.
For the efficiency to be $100 \%$,$Q_2$ must be $0$,meaning all heat absorbed from the source is converted into work.
This would require the sink temperature to be absolute zero $(0 \ K)$,which is unattainable according to the Third Law of Thermodynamics.
Therefore,some amount of heat must always be rejected to the sink,making $100 \%$ efficiency impossible.
According to the Second Law of Thermodynamics (Kelvin-Planck statement),it is impossible to construct a device that operates in a cycle and produces no effect other than the extraction of heat from a single reservoir and the performance of an equivalent amount of work.
For the efficiency to be $100 \%$,$Q_2$ must be $0$,meaning all heat absorbed from the source is converted into work.
This would require the sink temperature to be absolute zero $(0 \ K)$,which is unattainable according to the Third Law of Thermodynamics.
Therefore,some amount of heat must always be rejected to the sink,making $100 \%$ efficiency impossible.
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Which of the following statements is correct for any thermodynamic system?
The entropy of a thermodynamic system does not change when this system is used for:
$A$ solid body of constant heat capacity $1\,J/^{\circ}C$ is being heated by keeping it in contact with reservoirs in two ways:
$(i)$ Sequentially keeping in contact with $2$ reservoirs such that each reservoir supplies the same amount of heat.
$(ii)$ Sequentially keeping in contact with $8$ reservoirs such that each reservoir supplies the same amount of heat.
In both cases, the body is brought from an initial temperature $100^{\circ}C$ to a final temperature $200^{\circ}C$. The entropy change of the body in the two cases respectively is:
$(i)$ Sequentially keeping in contact with $2$ reservoirs such that each reservoir supplies the same amount of heat.
$(ii)$ Sequentially keeping in contact with $8$ reservoirs such that each reservoir supplies the same amount of heat.
In both cases, the body is brought from an initial temperature $100^{\circ}C$ to a final temperature $200^{\circ}C$. The entropy change of the body in the two cases respectively is:
Medium
View Solution$A$ measure of the degree of disorder of a system is known as
Easy
View SolutionThe graphs below show the entropy versus energy $U$ of two systems $1$ and $2$ at constant volume. The initial energies of the systems are indicated by $U_{1, i}$ and $U_{2, i}$,respectively. The graphs are drawn to the same scale. The systems are then brought into thermal contact with each other. Assume that,at all times,the combined energy of the two systems remains constant. Choose the most appropriate option indicating the energies of the two systems and the total entropy after they achieve equilibrium.
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