Physics Thermodynamics Note-taking Guide

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Oct 27, 2013 (3 years and 9 months ago)

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Physics Thermodynamics


Note
-
taking Guide

What does the law of conserva
tion of energy state? Energy is neither created nor destroyed, it merely
changes form.

What is the metric
base
unit of tem
perature? Kelvin

What is absolute zero? The temperature at
which no more energy can be extracted from a substance.

The coldest possible temperature = 0 K =
-
273 C

Describe the molecular motion of

a substance at absolute zero. There is no molecular motion.

W
hat is heat? Thermal energy being transferre
d from one su
bstance to another, due to differences in
temperature.

Which way does heat flow
? From hot to cold.

Describe the relationship between
temperature, kinetic energy, and
molecular motion. As the
temperature rises, the kinetic energy and molecular motion also
rise.

What is thermal equilibriu
m? When two substances reach the same temperature.

What is thermal

energy?

The internal energy of a substance that is related to the

What are the three laws of thermodynamics?

1) Whenever heat is added to a system, it tra
nsforms into an equal amount of some other form of
energy.

2) Heat will never of itself flow from a cold object to a hot object.

3) No system can reach absolute zero.



What are the two possibilities when heat energy is added to a system:

1) It increases t
he internal energy of a system.

2) It is converted to work done on something external to the sy
s
tem.


The first law of thermodynamics in equation
form:
Heat added = increase in internal energy + work

Describe an example of increasing the internal energy o
f a system wi
thout adding heat: Compressing a
ga
s in a diesel engine increases the temperature to the ignition point.

What is an adiabatic proce
ss? Compression or expansion of a gas without adding or removing heat.

What happens when a gas is c
ompressed adiabatically?

The temperature rises.

What happens when a gas dec
ompresses adiabatically?
The temperature falls.

Why

do these things happen? Compressing the gas does work, increasing the internal energy of the
system. Decompressing requires w
ork, decreasing the internal energy of the system.

How are pressure and tempe
rature related? As pressure rises, so does the temperature.

What is a heat engine? Any device that changes internal energy into work.

Every heat engine will:

1) Increase its
internal energy by absorbing heat from a high
-
temperature reservoir.

2) Convert some of this energy to mechanical work.

3) Expel the remaining energy as heat to some low
-
temperature reservoir (cold sink).


What is the Carnot efficiency of a hea
t engine? I
t is the percentage of input heat energy that is
converted into mechanical work.


Ideal efficienc
y =


Which temperature scale is used when calculating efficiency?

Kelvin

What creates the pressure difference across the blades of a turbine i
n a steam tu
rbine? The
temperature difference between the heat reservoir and the cold sink.

Does the Carnot equation give the actual, real
-
world efficiency of a
heat engine? No.

If not, what does it give us
? The theoretical maximum efficiency.

What is a reservoir of

a he
at engine? The source of heat energy. For example, a boiler.

What is the cold sink of a he
at engine? A source of cold that will absorb heat without warming it up.

What happens to the quality of energy as it goes through natural tr
ansformations? It
degrades.

What happens to the order of

systems over time? They naturally become more disordered.

What is entropy? A measure of the amount of disorder in a system.

Give an example (not from the book) of something naturally becoming more disordere
d over ti
me: The
human body degenerates slowly over time.

Give an example of doing work to make something more ordered:

Repairing a computer.

What is required to change disordered energy into ordered energ
y? Work.

What happens to the entropy
of systems over
time? It increases.

Which are more likely to happen, naturally, ordered states or disord
ered states? Disordered states.