Thermodynamics

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Oct 27, 2013 (3 years and 7 months ago)

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Thermodynamics

Thermodynamics

AP Physics Notes

2010
-
2011


Heat


Internal Energy


Work


Heat Reservoir / Heat Sink

Thermodynamics

Thermodynamics


Zeroth Law


First Law


Second Law

Thermodynamics


Adiabatic


Isobaric


Isochoric (Isovolumetric)


Isothermic

Thermodynamics


Carnot Theorem


Thermal Efficiency


Carnot Efficiency

Thermodynamics


Entropy


Reversible


Irreversible

Thermodynamics

Thermodynamics


Thermodynamics

-

study of properties and
movement of thermal energy (Q).




Q is measured in Joules like all other forms




of energy

Thermodynamics


Laws of Thermodynamics

-

each are
associated with a variable.


Zeroth law


Temperature, T


First law


Internal energy, U


Second law


Entropy, S

Thermodynamics

Thermodynamics

Thermodynamics


Adiabatic



A thermodynamic process that occurs
without gain or loss of heat

and without a
change in entropy



Look for gases that are insulated from
the environment



From Greek
a

“not“,
dia

“through”, and
batos

“passable”

Thermodynamics


Isobaric



A thermodynamic process that occurs
while the
pressure remains constant



From Greek
isos

"equal“ and
baros

"weight"


Thermodynamics


Isochoric (Isolvolumetric)



A thermodynamic process that occurs
while the
volume remains constant




Look for gases that are contained in a
closed or fixed container



From Greek
isos

"equal“ and
choro

"place"

Thermodynamics


Isothermal



A thermodynamic process that occurs
while the
temperature remains constant



Usually a relatively slow process to
allow the gas to maintain its temperature



From Greek
isos

"equal“




and
therme

"heat"

Thermodynamics


Combustion Engine

Thermodynamics


What is work as defined by the Collegeboard?


Work is the work done
by

a gas



Therefore…




Positive work is the compression of a gas




Negative work is expansion of a gas



What is work as defined by the textbook?


Work is the work done
on

a gas



To avoid confusion, we use the




Collegeboard’s definition only




Thermodynamics

W = P
D
V

In order for work to be accomplished by the gas, it
must expand or contract (change volume)

A change in pressure, only, will not result in any
work being accomplished


In most examples a piston or object atop the gas must
be moved for work to be accomplished



Since we are considering the work done by the gas, as
the piston moves, the gas loses energy



Expansion is negative work; contraction is positive
work

Thermodynamics

PV Diagram basics



P
(Pa)

V
(m
3
)

Thermodynamics

PV Diagram basics



P
(Pa)

V
(m
3
)

Given a point on the
diagram we can use

PV = nRT

to find the gas’s
temperature (K)

Thermodynamics

PV Diagram basics



P
(Pa)

V
(m
3
)

If we see a line or curve
connecting points then
we know the gas has
changed its properties in
some way

Thermodynamics

PV Diagram basics



P
(Pa)

V
(m
3
)

When we see an arrow
on that line, then we
know the original and
final states of the gas

Thermodynamics

PV Diagram basics



P
(Pa)

V
(m
3
)

Movement to the right
shows expansion
(remember this is
negative work)

Thermodynamics

PV Diagram basics



P
(Pa)

V
(m
3
)

Movement to the left
shows compression
(remember this is
positive work)

Thermodynamics

PV Diagram basics



P
(Pa)

V
(m
3
)

Movement directly
up or down shows
no change in
volume (remember
this is zero work)

Thermodynamics

PV Diagram basics



P
(Pa)

V
(m
3
)

When the path
closes then we
have one complete
cycle

The gas has
returned to its
original pressure,
temperature, and
volume

Thermodynamics

Rubber Bands as Spokes Engine

(
Explanation of Rubber Bands as Spokes Engine

)

Carnot Cycle and PV Diagram (Animation)

Ideal Diesel Engine (Animation)

A.
Be able to perform simple Carnot efficiency calculations.

B.
Be able to describe an ideal gas.

C.
Be able to interpret PV diagrams.

1.
Which part of the cycle has DU greater than zero?

2.
Which part of the cycle has Q greater than zero?

3.
Which part of the cycle W greater than zero?

4.
In which part of the cycle is no work done?

5.
At which part of the cycle is the gas at is highest temperature?

6.
What is the net work done?

7.
Which part of the cycle does the most work?

8.
Compare the temperatures at different points in the cycle.

9.
Which part of the cycle represents an adiabatic, isothermal,
isochoric (isovolumetric), or isobaric process?

D.
Be able to perform simple calculations using the ideal gas law or the
combined gas law. For example, pressure is doubled and volume is
quadrupled. What would be the relationship between the initial and final
temperatures?

E.
Know the characteristics of the processes.

F.
Predict what would happen to temperature if kinetic energy is changed.

G.
Be able to perform simple calculations using the first law of
thermodynamics.



Thermodynamics

A.
Be able to interpret PV diagrams.

1.
Use ideal gas law (or combined gas law) to calculate the temperature at
different points.

2.
Sketch the PV diagram from information given.

3.
Predict whether positive, negative, or no work is done for the cycle.

4.
Calculate the work done for the cycle (or part of a cycle).

5.
Calculate the heat absorbed or given off for a cycle (or part of a cycle).

6.
Predict which segments absorb the most heat.

7.
Predict if the cycle represents a heat engine or refrigerator.


B.
Remember the equation for power (P=W/t or P=Fv) and that P=F/A.


C.
Sometimes they ask about the rate at which heat is discarded by an engine.
This can be found knowing that W=QH
-
QL


D.
Be able to perform simple Carnot efficiency calculations.


Thermodynamics