*Thermodynamics
*Thermodynamics: the study of heat and its transformation into mechanical energy
*Internal energy: amount of thermal energy within an object
*Heat flows between objects, thermal energy resides in objects, temperature is a measure of average kinetic energy
*Thermal Energy: Conduction
*Conduction: heat transfer through objects touching
*Atoms collide and transfer energy
*Heat is transferred until the objects are at thermal equilibrium (same temperature)
*Thermal Energy: Convection
*Convection: heat transfer through moving currents in gases/liquids
*Hot gases and hot liquids rise, creating convection currents
*Thermal Energy: Radiation
*Radiation: heat transfer through electromagnetic radiation
*No matter necessary
*Can occur in a vacuum
*First Law of Thermodynamics
heat added
increase in
internal energy
external work done
by the system
= +
*Processes
*Adiabatic process: when a gas is compressed or expanded so that no heat enters or leaves a system
*Isothermal process: when the temperature of the system remains constant
*Heat Engines
*Heat engine: a device that changes internal energy (heat) into mechanical work
*Based on heat flowing from high temperature area (reservoir) to low temperature area (sink)
*Efficiency
*Ideal heat engine: converts internal energy completely into mechanical energy
*Carnot efficiency/ideal efficiency =
*Temperature measured in Kelvins
*Greater temperature difference greater efficiency
*Efficiency: Example
*If a steam engine has a heat reservoir temperature of 350 K and a sink temperature of 175 K, what is its ideal efficiency?
*ideal efficiency =
*Entropy
*Entropy: amount of disorder in a system
*Entropy tends to increase (2nd Law of Thermodynamics)
*Decreasing the entropy of a system requires work
*Multiple Choice #1
*The input heat in a heat engine is 600K(227 C) and the output is 300K(77 C). It’s ideal efficiency is:
*A) 25%
*B) 50%
*C) -50%
*D) 80%
*Multiple Choice #2
*How many calories are required to raise the temperature of 16 grams of water by 10 degrees C?
*A) 100 calories
*B) 120 calories
*C) 160 calories
*D) 200 calories
*Multiple Choice #3
*What is the rise in temperature when 20 calories are added to 10 grams of ice at -10 degrees C? Specific Heat of Ice: .5Cal/Grams X C
*A) 8 degrees C.
*B) 16 degrees C.
*C) 4 degrees C.
*D) 2 degrees C.
*Multiple Choice #4
*Ann is making pancakes. She burns her hand by touching the pan. What method of heat transfer explains this?
*A) Conduction
*B) Thermal Radiation
*C) Convection
*D) None of the above
*Multiple Choice #5
*How do you increase the internal energy of an object?
*A) Heat the system
*B) Do work on the system
*C) Both A & B
*D) None of the above
*Multiple Choice #6
*The First Law of Thermodynamics states that:
*A) when heat is added to a system, it will be lost
*B) when heat is added to a system, it will be transformed into twice as much energy
*C) when heat is added to a system, it will be transformed into an equal amount of energy
*D) adding heat is the only way to increase the internal energy of a system
*Multiple Choice #7
*Heat will flow:
*A) from cold to hot
*B) always upwards
*C) from hot to cold
*D) always downwards
*Multiple Choice #8
*The most efficient heat engine is one with:
*A) the smallest difference between input and output temperature
*B) a large difference between input and output temperature
*C) low input temperature and low output temperature
*D) high input temperature and high output temperature
*Multiple Choice #9
*The natural tendency of particles in a system is to:
*A) separate from different particles in the system
*B) continue moving in a straight line no matter what
*C) rapidly travel in small spirals
*D) create greater disorder
*Multiple Choice #10
*How is thermal energy transported from one place to another?
*I. Conduction
*II. Convection
*III. Radiation
A) I only
B) I and II only
C) II only
D) I, II and III