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PHYSICS I HONORS November 20 to December 8. CHAPTER 12 - Thermal Energy. |
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Plans for the Week and Assignments:
1. Friday(11/20): Physics Diagnostic Review I. Complete Review Handout
as Class-work. HW: Read pages 313-322, and Solve prob. 52, 53, 55,
60, and 63 on pages 336-337.
2. Monday(11/23): Physics Diagnostic Review II. Complete Review
Handout as Class-work. HW: Read pages 323-331, and Solve prob. 65, 67,
69, and 73 on pages 337-338.
3. Tuesday(11/24): Thermal energy, heat, temperature, and specific
heat capacity. HW: Read pages 313-322, and Solve prob. 52, 53, 55,
60, and 63 on pages 336-337, if you have not already done so.
Thanksgiving Vacation. Have a Safe and Happy Thanksgiving!
4. Monday(11/30): Changes of state, heats of fusion/vaporization, the
Laws of Thermodynamics, and Entropy. HW: Read pages 323-331, and
Solve prob. 65, 67, 69, and 73 on pages 337-338.
5. Tuesday(12/01): Lab activity on Heat of Fusion of Ice. HW: Process
lab data and solve application problems.
6. Wednesday(12/02): Post-Lab discussion. HW: Finish Lab Report
and write Abstract (due Thursday/Friday).
7. Thursday(12/03): The Laws of Thermodynamics, and Entropy.
HW: Read pages 323-331, and Solve prob. 65, 67, 69, and 73 on pages
337-338, if you have not already done so.
8. Friday(12/04): Review I for Chap.12 - Thermal Energy.
HW: Complete All Review Handouts.
9. Monday(12/07): Review II for Chap.12 - Thermal Energy.
HW: Complete All Review Handouts.
10. Tuesday(12/08): TEST on Chap.12 - Thermal Energy.
HW: Go to web-site for notes on Ch.13 - States of Matter.
Very Important: If you have any questions or miss a class, see
me before school (8:00 - 8:30 AM), during Lunch, or after school.
Best to send an email to rpersin@fau.edu.
WEBSITE NOTES: Ch.12 - Temperature and Heat Transfer.
1. The thermal energy of an object is the sum of the kinetic and potential
energies of the internal motion of its particles.
2. This is based on Kinetic Theory, which assumes that (i) all matter is
composed of tiny particles (atoms or molecules), and (ii) these particles
are in constant motion.
3. Heat is the thermal energy that is transferred by conduction during
particle collisions because of a difference in temperature. Since heat is a
form of energy, it is measured in Joules but can also be measured in
kilocalories (kcal) with the conversion factor being 1 kcal = 4186 Joules.
4. Temperature is a quantity proportional to the average kinetic energy
of the particles. Make sure you know the difference between heat,
temperature, and thermal energy.
5. Thermometers use some property of a substance, such as thermal
expansion, that depends on temperature, which in turn is used to
determine the direction of heat flow.
6. Two objects at the same temperature are said to be in thermal
equilibrium. This means that they will not exchange energy in the
form of heat.
7. The Celsius and Kelvin scales are widely used in scientific work.
One Kelvin is equal to one degree Celsius, and ΔTK = ΔTC. To change
a Celsius temperature to Kelvin use, TK = TC + 273.15.
8. The Kelvin (K), is named after William Thomson, Lord Kelvin (1824-
1907), British. The Celsius scale was devised by the Swedish astronomer
Anders Celsius (1704-1744) and was based on the properties of water.
9. At absolute zero, 0.0 K, or -273.15o C, matter has a minimum thermal
energy. This is regarded as the lowest temperature attainable.
10. Absolute zero was determined for the first time by the French scientist
Jacques Charles (1746-1823). The value of -273.15o C for absolute zero
was the result of his experiments on the relationship of the volume of a
gas to its temperature.
11. Most substances expand when heated and contract when cooled. This
applies to solids, liquids, and gases. Differences lie in the amount of heat
required to produce equal rates of expansion.
12. Each substance has its own ability to absorb and/or radiate heat.
This known as specific heat capacity, c , the quantity of heat needed
to raise the temperature of 1 kg of a substance 1 K. Water has one of
the highest. See page 318 for Specific Heat capacities.
13. In an isolated system, a quantity of heat, Q , can be exchanged
between substances but the total energy of the system is constant.
This is known as the Law of Heat Exchange, QL = QG .
14. The quantity of heat gained or lost by any material can be calculated
using the equation, Q = m·c·(Tf -Ti) , with m = mass, c = specific heat
capacity, and (Tf -Ti) being the temperature change, ΔT.
15. The Latent Heat of Fusion, Hf, is the amount of heat needed to change
1 kg of a substance from the solid to liquid state at its melting point.
16. The Latent Heat of Vaporization, Hv, is the amount of heat needed to
change 1 kg of a substance from the liquid to vapor state at its boiling
point. See page 324 for Latent Heats of Fusion and Vaporization.
17. Heat transferred during a change in state does not produce a change
in temperature and is therefore called called "latent", which means
hidden. The equations for each of these phase-changing processes is
Q = mHf or Q = mHv.
18. Convection is the process in which heat is carried from place-to-
place by the bulk movement of a fluid.
19. Conduction is the process whereby heat is transferred directly
through a material, with bulk motion of the material playing no role
in the transfer.
20. We have materials that are good conductors of heat, metals for
example. Materials that are poor conductors, wood, glass, and plastic,
are known as thermal insulators.
21. Radiation is the process in which energy is transferred by electro-
magnetic waves. All objects simultaneously absorb and emit radiant
energy. An object that is both a perfect absorber and emitter is called
a blackbody.
22. The First Law of Thermodynamics states that the total increase in
thermal energy of a system is equal to the sum of the heat added to it
and the work done on it, which is given by ΔU = (Uf -Ui) = Q-W.
23. A heat engine continuously converts thermal energy to mechanical
energy and the work done, W = P·ΔU = (Vf -Vi) , pressure times change
in volume .
24. A heat pump or refrigerator uses mechanical energy to transfer heat
from an area of lower to higher temperature.
25. The Second law of Thermodynamics states that natural processes
always go in a direction that increases the entropy, or disorder, of a
system or W = Q - ΔU = Q - (Uf -Ui).
26. The efficiency of a heat engine depends on the amount of energy
transferred by heat to and from the engine, or eff = Wnet/Qhot =
(Qhot-Qcold)/Qhot = 1 - Qcold/Qhot = 1 - Ti/Tf .
27. And still, we need these steps to solve any problem in Physics:
(i) read the problem and identify the given variables
(ii) determine what you are asked to solve for
(iii) find the correct motion formula to use
(iv) use algebra to isolate the unknown
(v) substitute-in the given information and simplify.
Here are the answers to the homework problems:
Pages 336-7: #52. 1.64x104 J #53. 1000 J/kg·K
#55. 171 J/kg·K #60. 15 kg #63. 29oC
Pages 337-8: #65. 290oC #67. 42%, 2900 J
#69. 12oC #73. 2.0x10-5 kg
THE
HONORS PHYSICS ARCHIVES
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And Always Remember... "From Newtonian Mechanics, Through Quantum Theory, Without Physics, Life Would Be Dreary." |
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