What went wrong when the king rode under the arch?

It was too low and knocked off his crown

How does the chain of blame unfold in the poem?

Each accused person blames another, ending with the king's own changes

State the zeroth law of thermodynamics.

If two systems are each in thermal equilibrium with a third system, they are in thermal equilibrium with one another, which lets temperature be defined.

State the first law of thermodynamics.

The heat supplied to a system equals the increase in internal energy plus the work done by the system, \(\Delta Q=\Delta U+\Delta W\).

What is internal energy and why is it a state variable?

It is the total molecular energy of a system; it depends only on the state, not on how the state was reached.

Relate the two molar specific heats of an ideal gas.

For an ideal gas \(C_p-C_v=R\), where \(R\) is the universal gas constant (Mayer's relation).

Distinguish isothermal and adiabatic processes.

In an isothermal process temperature is constant and heat is exchanged; in an adiabatic process no heat is exchanged and temperature changes.

State the Clausius statement of the second law.

Heat cannot flow of itself from a colder body to a hotter body without external work being done.

State the Kelvin-Planck statement of the second law.

No process is possible whose sole result is the complete conversion of heat from a reservoir into work.

Distinguish reversible and irreversible processes.

A reversible process can be retraced exactly through equilibrium states with no dissipation; real processes are irreversible due to friction and finite temperature differences.

Write the efficiency of a Carnot engine.

\(\eta=1-\dfrac{T_2}{T_1}\), depending only on the source and sink temperatures, not on the working substance.

Why is the Carnot engine the most efficient?

Because it is reversible; no engine working between the same two temperatures can have a greater efficiency (Carnot's theorem).

Thermodynamics

Class 11 Physics · Physics Part II · Chapter 4

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Summary

Thermodynamics studies the laws governing the conversion of heat into work and vice versa, dealing with macroscopic systems described by state variables such as pressure, volume and temperature. Two systems are in thermal equilibrium when they have the same temperature. The zeroth law of thermodynamics states that if two systems are each in thermal equilibrium with a third, they are in equilibrium with each other, which justifies temperature as a property. Heat and work are both forms of energy in transit; the internal energy of a system is a state variable. The first law of thermodynamics, \(\Delta Q=\Delta U+\Delta W\), is the principle of conservation of energy applied to heat. Specific heats at constant pressure and constant volume differ by \(C_p-C_v=R\) for an ideal gas. Thermodynamic processes include isothermal, adiabatic, isochoric and isobaric changes. The second law of thermodynamics expresses the one-way nature of heat flow: heat cannot flow spontaneously from a colder to a hotter body (Clausius), and no engine can convert heat completely into work (Kelvin-Planck). Processes are reversible or irreversible, and the Carnot engine, operating between two temperatures, has the maximum possible efficiency \(\eta=1-T_2/T_1\), independent of the working substance.

Thermal equilibrium and the zeroth lawHeat, internal energy and workFirst law of thermodynamicsSpecific heat capacityThermodynamic state variables and processesSecond law of thermodynamicsReversible and irreversible processesCarnot engine

Key terms

Internal energy

The total energy of a system stored in its molecules due to molecular motion and configuration; a state variable.

Zeroth law

The law stating that two systems each in thermal equilibrium with a third are in thermal equilibrium with each other.

First law of thermodynamics

The conservation of energy applied to heat, \(\Delta Q=\Delta U+\Delta W\).

Adiabatic process

A process in which no heat is exchanged with the surroundings (\(\Delta Q=0\)).

Second law of thermodynamics

The principle that heat cannot flow spontaneously from a colder to a hotter body and no engine can fully convert heat to work.

Carnot engine

An ideal reversible heat engine working between two temperatures with the maximum possible efficiency.

Extra questions & answers

Try one from this chapter

The first law of thermodynamics is expressed as:

Flashcards & interactive practice