Ch+10+-+Thermal+Physics

//Concepts discussed in this chapter include thermal equilibrium (zeroth law), thermal expansion of solids & liquids, ideal gas law and the kinetic theory of gases.//
 * Chapter 10 - Thermal Physics**

To understand Zeroth's law you must be able to identify what //thermal contact// and //thermal equilibrium// are. **Thermal contact** occurs when two objects come in contact with each other. If they are at different temperatures they will exchange energy, this is energy is called heat. **Thermal equilibrium** occurs when the exchange of this energy stops. Thus the zeroth law is defined as such:
 * Temperature and the Zeroth Law of Thermodynamics:**


 * __The Zeroth Law__** - If objects A and B are separately in thermal equilibrium with a third object C, then A and B are in thermal equilibrium with each other.

A thermometer, as most people know, measures the temperature of a system that is thermal equilibrium. A common thermometer may consist of a mass of liquid that expands when the temperature of the system rises. There are two different scales that measure temperature, **Celsius** and **Fahrenheit**. On the Celsius scale the temperature in which water freezes if found to be 0 degrees Celsius, and the boiling point of water is 100 degrees Celsius. On the Fahrenheit scale the freezing point of water is 32 degrees Fahrenheit, and the boiling point of water is 212 degrees Fahrenheit.
 * Thermometers and Temperature Scales:**


 * The Constant- Volume Gas Thermometer and the Kelvin Scale:**

A constant-volume gas thermometer measures the pressure of the gas in the bulb which is located in the bath ( P ). The volume of the gas in the bulb is kept constant by lowering the first reservoir to keep the mercury at a constant level.

By extending the graph formed from the constant-volume you can find the **triple point** of the substance.

__Triple Point__ - the single temperature and pressure at which water, water vapor and ice can coexist in equilibrium

Simply defined as when the temperature increases, the volume of the material also increases proportionally. WHICH CAN BE REPRESENTED BY THIS EQUATION: L0= original length T= change in temperature** //See Table 10.1 on page 313 for average coefficient of thermal expansions for some materials//
 * Thermal Expansion**
 * L=aL0**T
 * a= coefficient of linear expansion

Applying this to real you can look at thermostat. Two

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 * Ideal Gas Law

This is a view of the Ideal Gas Law in terms of the behavior of the individual molecules that make up the gas. The kinetic theory is used to describe pressure and temperature of an ideal gas in terms of microscopic variables. The kinetic theory is based on 5 assumptions: 1. The number of molecules in the gas is, and the average separation between them is large compared with their dimensions. 2. The molecules obey Newton's Laws of Motion, but as a whole they move randomly. 3. The molecules interact only by short-range forces during elastic collisions. 4. The molecules make elastic collisions with the walls. 5. The gas under construction is a pure substance and that all molecules are identicle.
 * Kinetic Theory of Gases**

An equation that is derived from these assumptions is: P=2/3(N/V)(½mv²) This equation explains that pressure is proportional to the number of molecules per unit of volume and the average kinetic energy of the molecule.

By relating temperature to kinetic energy, the formula is created: ½mv²=3/2kT This equation is the average kinetic energy per molecule and proves that the temperature of a gas is directly related to the average kinetic energy.

The average kinetic energy is equal to the internal energy of the system, U U=3/2nRT

__Summary Equations__ Boltzmann's Constant = 1.38×10^-23 J/K N = 6.02×10^23 particle/mol R = 8.31 J/mol×K
 * Constants**

Tc+273.15⁰K
 * Celsius to Kelvin**

Tf = 9/5 Tc+32
 * Fahrenheit to Celsius**

ΔL = αLoΔT (T is in ºC) α = Coefficient of Linear Expansion
 * Coefficient of Linear Expansion**

ΔA = λAoΔT λ=Coefficient of Area Expansion (2α)
 * Coefficient of Area Expansion**

= = ΔV = βVoΔT β = Coefficient of Volume Expansion (3α or 2λ)
 * Coefficient of Volume Expansion**

PV=nRT
 * Ideal Gas Law**

½mv²=3/2kT U=3/2nRT - Internal Energy
 * Average Kinetic Energy**