Beta Physics Class Notes

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Heat and Thermodynamics Notes

3/10/09

Beta Physics Class Notes

Heat and Thermodynamics



Chapter 14: Heat

Major Topics

Thermal energy, internal energy, heat




Specific heat, calorimetry

Heat transfer mechanisms




Conduction, convection, radiation

In Textbook

READ
Sections 14.1
-
14.2, 14.4
-
14
.9

Lab:



Newton’s Law of Cooling

Problem Set 14:

pp. 438
-
442 Q 26, 28; Problems 3, 9, 15, 23, 51



Chapter 15: Thermodynamics

Major Topics

Laws of Thermodynamics




Heat Engines




Applications like heat pumps, refrigerators, engines

In Textbook

READ
Sec
tions 15.1
-
15.2, 15.4
-
15.9

Presentations:

Small group PowerPoints on thermo applications

Problem Set 15:

pp. 471
-
4 Q 8, 15, 19, p. 473, Problems 17, 19, 24, 52










Equations and conversion factors for Heat and Thermodynamics






GPE = mgh


Q = mc∆T



K = ºC + 273.15



1 calorie = 4.186 J



Heat and Thermodynamics Class Notes

p.
2


Mechanical Equivalent of Heat


Joule's apparatus for measuring the mechanical equivalent of heat.


“In 1845, the English physicist James Joule wrote a paper on the mechanical equiv
alent of
heat for the British Association meeting in Cambridge. In this work, he reported his best
-
known experiment, in which the work released through the action of a "weight falling
through a height" was used to turn a paddle
-
wheel in an insulated barrel

of water.


In this experiment, the friction and agitation of the paddle
-
wheel on the body of water
caused heat to be generated which, in turn, increased the temperature of wat
er. Both the
temperature change ∆T of the water and the height of the fall ∆h of the weight mg were
recorded. Using these values, Joule was able to determine the mechanical equivalent of
heat.”

http://schools
-
wikipedia.org/wp/w/Work_%2528thermodynamics%252
9.htm


Mechanical Energy

A 10.0 kg weight drops 2.0 m. What is
the potential energy of the weight before
if falls?



How much work does the falling weight
do?


If the energy transfer is 100% efficient,
what is the kinetic energy of the paddle
wheel?

Heat

The barrel of water contains 20.0 g of
water, which has a specific heat of 1.0
cal/g ºC. The water temperature
increases by 2.35 ºC. How many calories
of heat were transferred to the water?




Mechanical Equivalent of Heat =


Heat and Thermodynamics Class Notes

p.
3


Im
portant terms and concepts for Chapter 14 & 15





Definition






Equation

Units

Thermal Energy

Internal Energy



Heat



Temperature



Specific Heat



Calorimetry



Heat of Fusion



Heat of Vaporization



Conduction



Convection



Radiation



What is the
difference between heat and temperature?



How does heat transfer and why?


What are the possible units of heat and energy and how are they
related?


How do you measure heat changes?


Heat and Thermodynamics Class Notes

p.
4


What happens when you add heat to a solid?


What happens

From A to B

Fro
m B to C

From C to D

From D to E

From E to F


What do you notice
about phase changes?




Label this graph
with the
numbers and letter of the
problems below, to show
what part of the graph
represents the changes you
are calculating.


http://china
-
heatpipe.n
et/heatpipe04/08/2008
-
1
-
31/Lat ent_Heat.htm

Questions About Heat


1.

You went to the big box store Thermo City and bought 10.0 kJ of heat, on sale.

A. If you used your heat to increase the temperature of 250 g of water at 1ºC, what final
temperature woul
d it reach?






B. How hot would a 250 g block of aluminum at 1ºC get, if you used your heat to
increase its temperature?





C.

What is the difference between water and aluminum, that accounts for the difference
in the final temperature?




2.

You retur
ned to Thermo City and bought 10.0 kJ more heat, to continue your fun.


Heat and Thermodynamics Class Notes

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5


A. If you used your heat to melt ice to liquid water at 0ºC, how many grams of ice could
you melt?






B

If you used your heat to vaporize liquid water to water vapor at 100ºC, ho
w many
grams of water could you vaporize?






C.

If you needed it, how could you get your 10.0 kJ of heat BACK, at the end of your
experiments in parts A and B?










http://www.thesciencedesk.com/studyguidephasechanges.htm


Heat and Thermodynamics Class Notes

p.
6


Heat Transfer Mechanisms



http://www.beodom.com/en/journal/entries/principl es
-
of
-
thermal
-
i nsulation
-
heat
-
transfer
-
via
-
conduction
-
convection
-
and
-
radi ation


What are the 3 mechanisms for heat transfer and how do they work?

1.



2.



3.



Heat Transfer Questions

1.

Sea breezes are oft
en encountered on sunny days at the shore of a large body
of water. Explain in light of the fact that the temperature of the land rises more
rapidly than that of the nearby water.






2.

Why is the liner of a thermos bottle silvered (Fig. 14
–
15), and why doe
s it have a

Heat and Thermodynamics Class Notes

p.
7


vacuum between its two walls?











3.

A piece of wood lying in the Sun absorbs more heat than a piece of shiny metal.
Yet the wood feels less hot than the metal when you pick it up. Explain.
































http://www.aos.wisc
.edu/~aalopez/aos101/wk5.html


Heat and Thermodynamics Class Notes

p.
8


Newton’s Law of Cooling

Newton's law of cooling, states that the _________ of heat loss of a body is proportional to the
difference in ______________ between the body and its surrounding. The law will allow you to
predict the

temperature after time has elapsed.


The mathematical form of Newton’s Law of Cooling is




In your lab, you fit your data to a __________________ function.


The constant k is related to the system’s __________________, ___________________ and
___________
_________.


This graph compares the temperature change with time when you add cream to your coffee.




How can your keep your
coffee as hot as possible?






























http://www.kritzinger
-
home.com/cooling.html

Heat and Thermodynamics Class Notes

p.
9



http://www.grc.nasa.gov/WWW
/K
-
12/airplane/thermo.html


What are the 3 Laws of Thermodynamics?

1.




2.




3.






Heat and Thermodynamics Notes

p.
14

Chapter 15: Heat Engine Review Questions and Problems


1.

Explain what this diagram illustrates about heat
engines. Give a specific example of the
reservoirs, the source
and loss of heat, and the
work done. What does this diagram have to do
with the 2nd Law of thermodynamics?



2.

What is the maximum efficiency of a heat engine with a high T reservoir at 401 K
and a low T reservoir at 273 K?





3.

Explain what type of devi
ce this diagram
illustrates. Give a specific example of the
reservoirs, the source and loss of heat, and the
work done.






4.

How can the above device move heat from a low to a high temperature region?
What law of thermodynamics says how this can be acco
mplished? (Hint: Find
the Clausius statement of this law, for the most complete answer).








Heat and Thermo Cl ass Notes

p.
15

Chapter 14: Heat Review Questions and Problems

1.

How much heat (in joules) is required to raise the temperature of 30.0 kg of
water from 15°C to 95°C?



2.

A water h
eater can generate

How much water can it heat from 15°C
to 50°C per hour?




3.

If you add some heat to a substance, is it possible for the temperature of the
substance to remain unchanged? Explain.




4.

An “emergency blanket” is a thin

shiny (metal coated) plastic foil. Explain how
it can help to keep an immobile person warm.




5.

Given your experience of what feels colder when you walk on it, which of the
surfaces would have the
highest thermal conductivity?

a
a
.
.


a rug


b.

a steel surface

c.

a concr
ete floor

d.

has nothing to do with thermal conductivity



6.

On his honeymoon, James Joule attempted to explore the relationships
between various forms of energy by measuring the rise of temperature of
water which had fallen down a waterfall on Mount Blanc. Wh
at maximum
temperature rise would one expect for a waterfall with a vertical drop of 20 m?


a.

0.047 C°


b.

0.053 C°


c.

0.064 C°


d.

0.071 C°



7.

Convection can occur


a.

only in solids.


b.

only in liquids.


c.

only in gases.


d.

only in liquids and gases.


e.

in solids, liquids
, and gases

.



Heat and Thermo Cl ass Notes

p.
16

I want YOU to study for the Chap. 14 & 15 test


To prepare for the test, you should

1.

Complete the 14 & 15 homework.

2.

Do all the problems in the class
notes handout.

3.

Review the Introduction to Heat
and Thermo page.

4.

Do the Reality Check questi
ons
and problems.

5.

Go over your Newton’s Law of
Cooling Lab.

6.

Review the appropriate sections of
your textbook

Terms and Concepts

Internal energy, thermal energy, heat, temperature, specific heat, mechanical
energy, latent heat, entropy

Specific Heat and Ca
lorimetry

Q = mc∆T, calculating temperature change for given amount of heat, calculating
specific heat, comparing materials with different specific heats

Energy Transformations

PE, KE, and W to heat calculations, molecular mechanism of friction, units of
heat and en
ergy and interconversion, mechanical equivalent of heat

Heat Transfer Mechanisms

Conduction, convection, and radiation mechanisms and examples

How can you reduce or increase each type of heat transfer?

Newton’s Law of Cooling

T = (T
0
-
T
room
)e
–
kt

+ T
room

gra
ph and equation

Calculate T at given t and t for given T

Explain meaning of k, how to change its value, 2 ways to change cooling rate

Laws of Thermodynamics

State 0
th
, 1
st
, 2
nd
, and 3
rd

and give an example that illustrates each

Calculations using 1
st

Law
Q
in

= W + Q
out

Entropy concept and 2
nd

Law

Heat Engine

Diagram with hot and cold reservoirs, work done, example engine

Calculating the efficiency using Eff = 1
–

T
c
/T
h

What is the limit of efficiency and why?

Applications of Thermodynamics

How they work:
refrigerator, air conditioner, heat pump, heat engine

Relate to 1
st

and 2
nd

Law, draw heat engine diagram

How do heat engine and refrigerator differ? How are they the same?