Thermodynamics – branch of physics concerned
with the study of both thermal and mechanical
(or dynamical) concepts.
Application: Steam Engines in 1800’s
Adiabatic Example:
When a particular piston is released, it expands
adiabatically, lifting a weight. The internal energy
goes down 10 J. How high was the weight lifted?
Isobaric Example:
Air in a balloon heats up and expands from 0.1 m3
to 0.2 m3 at atmospheric pressure. How much
work is done on the gas?
Isovolumetric Example:
10 g of steam is heated 5°C in a closed container.
What is the change in the internal energy of the
steam?
Isothermal Example:
An ideal gas expands from 2.0 m3 to 3.0 m3 at
constant temperature. What is the work done by
the gas?
4-Stroke Engine:
https://www.youtube.com/watch?v=SYd40qWQ9Bc
Different ways that compressions, expansions, etc. can
occur:
• Adiabatic
• Isothermal
• ….
What happens to the temperature of the air that
is let out of a car tire?
1. it increases.
2. it decreases.
3. it remains the same.
Consider a cylinder divided into two parts by a
membrane. On one side of the membrane is a
gas at a pressure P, and temperature T. The
other side is evacuated. If the membrane
vanished, the gas would rush to fill the
evacuated side, and its temperature would
1. increase.
2. decrease.
3. remain the same.
If a system does work adiabatically,
1. the temperature stays the same.
2. the internal energy stays the same.
3. the internal energy decreases.
4. the internal energy increases.
5. none of the above.
A cylinder and piston contains a gas that is made to
expand from A to B at a constant temperature as shown
below.
A
P
B
V
This process is
1. adiabatic and heat leaves the gas.
2. isothermal and heat enters the gas.
3. adiabatic and heat enters the gas.
4. isothermal and heat leaves the gas.
5. none of these.
A gas in a piston is compressed adiabatically
by a force of 500 N acting through a distance
of 5 cm. The net change in the internal
energy of the gas is
1. +500 J.
2. +25 J.
3. -500 J.
4. -25 J.
5. none of the above.
An adiabatic process is one that occurs without
changes in
1.
2.
3.
4.
Pressure
Density
Temperature
Energy by heat
If a gas is compressed isothermally, which of the
following statements is true?
1.
2.
3.
4.
Energy is transferred into the gas by heat.
No work is done on the gas.
The temperature of the gas increases.
The internal energy of the gas remains
constant.
5. None of those statements is true.
A piston is quickly pushed downward. This
process is best described by:
1.
2.
3.
4.
5.
Adiabatic
Isothermal
Constant energy
None of the above
Two of the above
One mole of an ideal gas is placed in a copper
cylinder and piston setup. The piston is slowly
lowered until the pressure has doubled. This
process is best described as:
1.
2.
3.
4.
5.
Adiabatic
Isothermal
Constant energy
None of the above
Two of the above
Estimate the total work by a system taken
around the cycle shown in the figure. Does the
system have to be an ideal gas?
Conduction Example:
An air-bake cookie sheet consists of a top and
bottom aluminum sheet, separated by a thin
layer of air. The aluminum sheets are both 3 mm
thick and they are separated by 5mm. The cookie
sheet has a length and width of 20 cm. If place
on a stove at 200°C, how much energy reaches
the top of the cookie sheet each minute?
kAl = 238 W/m°C
Kair = 0.0234 W/m°C
Conduction Example:
One side of a 0.1 m thick aluminum block rests
on a 20°C table. A piece of glass is placed on top
of the aluminum to separate it from an object
held at 2000°C. If aluminum melts at 660°C, how
thick does the glass need to be to keep the
aluminum from melting?
kAl = 238 W/m°C
Kglass = 0.8 W/m°C
Radiation Example:
A ball (r = 1 cm, e = 0.4) initially at 300 K is
suspended in a vacuum chamber that is kept at
77 K by liquid nitrogen. What is the initial rate of
energy lost by the ball?
Two brick walls have the same surface area,
but wall A is twice as thick as wall B. If the
temperature difference between the sides of
wall A is twice the temperature difference
between the sides of wall B, the rate of heat
transfer is
1. greater for wall A.
2. greater for wall B.
3. the same for walls A and B.
The purpose of a cover on a soup kettle is to
1. increase conductivity.
2. decrease convection.
3. increase radiation.
4. decrease conduction.
5. none of these.
A moistened finger will stick to a lamppost on a
very cold day, but it won’t stick to wood. The
reason has to do with
1. the difference in specific heats.
2. the difference in thermal conductivity.
3. the difference in temperatures.
4. the latent heat of fusion.
5. none of the above.
The figure shows a test tube containing
water and some ice (held down by a
weight). As shown, the water at the
top is boiling. Is that possible, and, if
so, why?
1. yes, because the water has a high
heat of vaporization.
2. no, because the water has a low
specific heat capacity.
3. yes, because the water has a low
thermal conductivity.
4. no, because the water has a low heat
of fusion.
5. none of these.
Water
Ice
Suppose you pour a cup of hot coffee and the
phone rings so you can’t drink it. To keep it hot
as long as possible,
1. add the cool milk and sugar immediately.
2. don’t add the cool milk and sugar until you are
ready to drink it.
For ease of use and safety, a fireplace poker
should be made from a material
1. with high specific heat and high thermal
conductivity.
2. with low specific heat and low thermal
conductivity.
3. with low specific heat and high thermal
conductivity.
4. with high specific heat and low thermal
conductivity.
Why does ice form on a bridge before it does on
the rest of the road?
1. conduction.
2. convection.
3. radiation.
4. none of these, because the ice freezes without
changing temperature.
Problem:
A 2-mol sample of helium gas initially at 300 K
and 0.400 atm is compressed isothermally to
1.20 atm. Noting that the helium behaves as an
ideal gas, find:
a) The final volume of gas.
b) The work done on the gas.
c) The energy transferred by heat.