Reading Quiz
• A container of helium gas is heated,
raising the temperature of the gas. This
causes
• the average kinetic energy of the gas molecules
to increase.
• the average potential energy of the gas
molecules to increase.
• the average acceleration of the gas molecules to
increase
The internal energy U of a system is increased by
the transfer of either heat or work into the system.
U  Q  W
Frist Law of Thermodynamics
Internal Energy = Added Heat - Work done by the system
A falling mass turns a paddle in an insulated beaker of
water in this schematic representation of Joule’s
apparatus for measuring the temperature increase
produced by doing mechanical work on a system.
Steam issuing from the kettle makes the pinwheel
turn in this simple steam turbine. Work could be
done to lift a small weight with such an engine.
Heat released by
burning gasoline in the
cylinder of an
automobile engine
causes the piston to
move, converting some
of the heat to work.
The internal energy U of a system is increased by
the transfer of either heat or work into the system.
Zeroth Law of Thermodynamics
Two objects in thermal equilibium have the same temperature
What is INTERNAL ENERGY?
The internal energy of the system is the sum
of the kinetic and potential energies of the
atoms and molecules making up the system.
The First Law of Thermodynamics:
The increase in the internal energy of a system is
equal to the amount of heat added to the system,
plus the amount of work done on the system.
The increase in the internal energy of a system is
equal to the amount of heat added to the system,
minus the amount of work done by the system.
U = Q - W
Q=heat add to system
W = work done by system
Quiz 1
The first Law of Thermodynamics, U = Q - W, means:
A. Heat cannot be added to a system without work being
done.
B. Work cannot be done without heat being added.
C. The amount of work done always equals the amount
of heat added.
D. The total internal energy of a system is conserved.
E. All of the above
F. None of the above are true.
CHOOSE THE TRUE STATEMENT.
Work done by a movable piston
Work=F x d = F/A x d x A = P V
Quiz 2
•
1.
2.
3.
4.
5.
If the temperature of a gas is held constant
during compression or expansion it is
called
Equation of state
Isobaric
Isothermal
Thermal conductivity
convection
Convection
Motion of a fluid
Quiz 3
Heat can be transferred by
1.
2.
3.
4.
5.
Thermal Conduction
Convection
Radiation
All of the above
None of the above
Head Flow
Heat Transfer
What is a heat engine?
• Thermal heat QH is introduced into the engine.
• Some of this is converted into mechanical work,
W.
• Some heat is released into the environment at a lower temperature, QC.
What does the First Law tell us about heat engines?
U = Q - W = QH - QC -W
, the internal energy U of a heat
engine does not change from cycle to cycle, so U =0.
Hence, Q = W.
The net heat flowing into the engine equals the work done by
the engine:
W = QH - QC
The Second Law of Thermodynamics
The Carnot engine is an ideal system which turns out to have the
maximum possible efficiency:
If TH is the hottest temperature in the engine, and TC is temperature
outside the engine (in Kelvin), then the efficiency is:
ec = (TH - TC )/ TH
=W/QH
This shows that it is not possible too have an efficiency of 100%. You
always lose some energy into heating the environment.
This can be restated as a version of the Second Law:
No engine, working in a continuous cycle, can take heat from
a reservoir at a single temperature and convert that heat
completely into work.
A restatement of the Second Law which turns out to be
equivalent:
Heat will not flow from a colder body to a hotter body unless
some other process (which does work) is also involved.
Another restatement to be discussed next time:
The entropy of an isolated system can only increase or
remain constant. Its entropy cannot decrease.
According to the Second Law of Thermodynamics,
heat will not flow from a colder body to a warmer
body.
1. True
2. False
According to the Second Law of Thermodynamics,
heat will not flow from a colder body to a warmer
body.
1. True
2. False
A schematic representation
of a heat engine. Heat is
taken in at high
temperatures, TH. Some
heat is converted to work,
and the remainder is
released at a lower
temperature, TC.
The arrow widths depict the quantities of
energy in the sample exercise in box 11.1.
The efficiency of a heat engine is defined as
e = W/ QH .
Engines are more efficient if there is a large
difference between the high temperature inside
and the low temperature outside.
For an ideal heat engine,
ec = (TH - TC )/ TH