University Physics Volume 2

# Summary

### 1.1Temperature and Thermal Equilibrium

• Temperature is operationally defined as the quantity measured by a thermometer. It is proportional to the average kinetic energy of atoms and molecules in a system.
• Thermal equilibrium occurs when two bodies are in contact with each other and can freely exchange energy. Systems are in thermal equilibrium when they have the same temperature.
• The zeroth law of thermodynamics states that when two systems, A and B, are in thermal equilibrium with each other, and B is in thermal equilibrium with a third system C, then A is also in thermal equilibrium with C.

### 1.2Thermometers and Temperature Scales

• Three types of thermometers are alcohol, liquid crystal, and infrared radiation (pyrometer).
• The three main temperature scales are Celsius, Fahrenheit, and Kelvin. Temperatures can be converted from one scale to another using temperature conversion equations.
• The three phases of water (ice, liquid water, and water vapor) can coexist at a single pressure and temperature known as the triple point.

### 1.3Thermal Expansion

• Thermal expansion is the increase of the size (length, area, or volume) of a body due to a change in temperature, usually a rise. Thermal contraction is the decrease in size due to a change in temperature, usually a fall in temperature.
• Thermal stress is created when thermal expansion or contraction is constrained.

### 1.4Heat Transfer, Specific Heat, and Calorimetry

• Heat and work are the two distinct methods of energy transfer.
• Heat transfer to an object when its temperature changes is often approximated well by $Q=mcΔT,Q=mcΔT,$ where m is the object’s mass and c is the specific heat of the substance.

### 1.5Phase Changes

• Most substances have three distinct phases (under ordinary conditions on Earth), and they depend on temperature and pressure.
• Two phases coexist (i.e., they are in thermal equilibrium) at a set of pressures and temperatures.
• Phase changes occur at fixed temperatures for a given substance at a given pressure, and these temperatures are called boiling, freezing (or melting), and sublimation points.

### 1.6Mechanisms of Heat Transfer

• Heat is transferred by three different methods: conduction, convection, and radiation.
• Heat conduction is the transfer of heat between two objects in direct contact with each other.
• The rate of heat transfer P (energy per unit time) is proportional to the temperature difference $Th−TcTh−Tc$ and the contact area A and inversely proportional to the distance d between the objects.
• Convection is heat transfer by the macroscopic movement of mass. Convection can be natural or forced, and generally transfers thermal energy faster than conduction. Convection that occurs along with a phase change can transfer energy from cold regions to warm ones.
• Radiation is heat transfer through the emission or absorption of electromagnetic waves.
• The rate of radiative heat transfer is proportional to the emissivity e. For a perfect blackbody, $e=1e=1$, whereas a perfectly white, clear, or reflective body has $e=0e=0$, with real objects having values of e between 1 and 0.
• The rate of heat transfer depends on the surface area and the fourth power of the absolute temperature:
$P=σeAT4,P=σeAT4,$

where $σ=5.67×10−8J/s·m2·K4σ=5.67×10−8J/s·m2·K4$ is the Stefan-Boltzmann constant and e is the emissivity of the body. The net rate of heat transfer from an object by radiation is
$Qnett=σeA(T24−T14),Qnett=σeA(T24−T14),$

where $T1T1$ is the temperature of the object surrounded by an environment with uniform temperature $T2T2$ and e is the emissivity of the object.