Important Terms & Notes

Conceptual PhysicsMar. 17, 2014

Entropy

• A measure of the amount of disorder in a system.

ΔS = Δ Q/T

Entropy

• The idea of ordered energy tending to disordered energy?

• What is Ordered or Organized Energy?• Energy that can be transformed or used to

perform work• What is Disordered energy?• Energy that has been transformed into a non-

usable form (“Waste Energy”).

Entropy

• Natural Systems tend to proceed toward a state of greater disorder.

• Examples:• The Universe after the BIG BANG.• Organic decomposition: Food Rotting• Ice cube Melting• Dye into a glass of water.• One’s Messy Room??

Entropy

• Increasing or Decreasing, Reversible or irreversible:

• Liquid water becoming Ice Cubes? Under what circumstances?

• A log Burning?• Pushing a heavy block across the floor?• Air Molecules being blown into a balloon?• Air Molecules escaping out of a balloon?

Entropy

• How does one reverse Entropy???• Can one Reverse Entropy??

First Law of Thermodynamics

• Heat added to a system is transformed into an equal amount of some other form of energy.

• A version of the Law of Energy Conversion

ΔQ = ΔEi + W

Second Law of Thermodynamics

• Heat will never of itself flow from one object to another of higher temperature.

• Heat will not flow from Cold to Hot without work being performed.

The Laws of Thermodynamics

• You CAN’T Win – because you can not get any more Energy out of a

system than you put in• You CAN’T Break even– because you can even get the same amount of

Energy out of a system that you put in• You CAN’T Get Out of the Game– Because entropy in the Universe is always

increasing

Adiabatic

• The term applied to the expansion or compression of a gas occurring without the gain or loss of heat.

• Example: Activity within the Cylinders of an Internal Combustion Engine

Heat Engine

A Device that Changes Internal Energy into Mechanical Energy

The Heat Engine

Carnot engine diagram (modern) - where heat flows from a high temperature TH furnace through the fluid of the "working body" (working substance) and into the cold sink TC, thus forcing the working substance to do mechanical work W on the surroundings, via cycles of contractions and expansions.

Carnot Efficiency

• The Ideal maximum percentage of input energy that can be converted into work in a heat engine.

• Ideal Efficiency = (Thot – Tcold)/Thot

Chapter 24 Review QuestionsQuestions 1 - 8

1. Greek meaning: Movement of Heat2. Thermodynamics is concerned with

Macroscopic processes. 3. Lowest possible temperatures:

a. On Kelvin scale : 0° K b. On Celsius Scale: -273° C

4. Temperature of Melting Ice on the Absolute Scale: +273 ° K

Chapter 24 Review QuestionsQuestions 1 -8 (cont.)

4. Temperature of Boiling Water on the Absolute Scale: +373 ° K

5. Energy cannot be created nor destroyed; therefore , Energy (Heat) added to a system can only change to an equal amount of another form of energy.

ΔQ = ΔE +W

Chapter 24 Review QuestionsQuestions 1 -8 (cont.)

6. Work done on a system should result in an increase of the Internal Energy of that System. The temperature of that system should increase as well since the average kinetic energy of the system has increased.

7. ΔQ = ΔEi + W

8. Work done on a system should result in an increase in the Internal Energy of that System. Work done by a system should result in an decrease in the Internal Energy of that System.

Chapter 24 Review QuestionsQuestions 9 - 16

9. No Heat is gained or Lost by the System.10a. The Air temperature increases during adiabatic compression.10b. The Air temperature decreases during adiabatic expansion.11. The temperature of rising air generally cools as it rises.

Chapter 24 Review QuestionsQuestions 9 - 16 (cont.)

12. The temperature of falling air generally increases as it rises.

13. Since heat , of itself, will only flow from hot to cold, in order to force heat to flow from cold to hot work MUST be performed.

14. Three processes occurring in every heat engine High Temperature, Low temperature,

Work Done

Chapter 24 Review QuestionsQuestions 9 - 16 (cont.)

15. Thermal Pollution is the undesirable heat expulsion from a process.16. No. According to the Carnot Efficiency (which is based on the temperature difference between processes) a Heat Engine cannot achieve 100% efficiency even if the effects of friction are removed.

Ideal Efficiency = (Thot – Tcold)/Thot

Chapter 24 Review QuestionsQuestions 17 - 25 (cont.)

17.Eff= (Thot – Tcold)/Thot in KELVINS: 40%18.To Increase efficiency19.Organized Energy: Electricity used to heat a

room, A car breaking to stop…WHY???20. 100% we perceive some of that energy

transformation as light. 21.Natural Systems: Tend to Disorder. Disordered

state will tend to order only when work is applied

Chapter 24 Review QuestionsQuestions 17 - 25 (cont.)

22. Messy Physicist: Dr. Entropy23. Decrease in Entropy: With organized Energy input or work done on the system.24. Entropy increases in natural systems.25. 1st Law: No exceptions 2nd Law: Exceptions may occur under proper circumstances.