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.

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ΔU =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 ThermodynamicsTwo 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.

ΔU = Q - W

Q=heat add to system

W = work done by system

Quiz 1

The first Law of Thermodynamics, ΔU = 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 ΔV

Quiz 2

• If the temperature of a gas is held constant during compression or expansion it is called

1. Equation of state2. Isobaric3. Isothermal4. Thermal conductivity5. convection

ConvectionMotion of a fluid

Quiz 3

Heat can be transferred by1. Thermal Conduction

2. Convection

3. Radiation

4. All of the above

5. 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?

ΔU = Q - W = QH - QC -W

, the internal energy U of a heat engine does not change from cycle to cycle, so ΔU =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