Physics 52 - Heat and Optics Dr. Joseph F. Becker Physics Department San Jose State University © 2003 J. F. Becker

Chapter 20 The Second Law of Thermodynamics

Schematic energy-flow diagram for a heat engine.

Cycle of a four-stroke internal- combustion engine: intake, compression, power, exhaust.

The pV diagram for the Otto cycle, an idealized model of the thermodynamic processes in a gasoline engine.

The pV diagram for the idealized Diesel cycle.

Schematic energy-flow diagram for a refrigerator.

Principle of a mechanical refrigeration cycle.

AC works on same principle as a refrigerator

Energy-flow diagrams for equivalent forms of the Second Law of Thermodynamics.

The Carnot cycle for an ideal gas. Isotherms in light-blue. Adiabats in dark-blue.

Second Law forbids this system.

Water molecules are arranged in a regular ordered way in an ice crystal.

Free expansion of an insulated ideal gas. In (c) the free-expansion process does not pass through equilibrium states from a to b. However, the entropy change S b – S a can be calculated by using the isothermal path shown or any reversible path from a to b.

(a) A reversible cyclic process for an ideal gas, shown as a red closed path. (b) The path can be approximated by a series of long thin Carnot cycles. The entropy change is zero for each Carnot cycle and for the actual cyclic process. (c) The entropy change S b – S a is the same for all paths connecting points a and b.

All possible microscopic states for 4 coins. There can be several microscopic states for each macroscopic state.

In a free expansion of N molecules in which the volume doubles, the number of possible microscopic states increases by 2 N

A passive solar collecting panel for home water heating.

A heat engine takes mol of a diatomic ideal gas around the cycle.

Thermodynamic Processes for a Refrigerator.

A Stirling-cycle engine.

Fuel Economy and Automobile Performance.

Review