Chapter 1
Energy –
the driving force of change
Energy is the driving force for all changes: winds, rains, storms, thunders, forest fires,
earthquakes, waves, plant growth, food decay, ocean tides, formation and melting of ice,
combustion, and growing old to name just a few. Furthermore, nuclear changes such as
radioactivity, nuclear fission, and nuclear fusion (reactions) are also driven by energy. Energy,
unlike matter, has no weight, size, shape, color or appearance, and its recognition is difficult.
There are still some aspects about energy we do not fully understand.
Energy is the heart of nuclear technology,
because all nuclear phenomena are caused
by energy. In fact, the amount of energy
involved in nuclear technology is so large
that it scares us. We, the human race, have
the nuclear technology to destroy the
civilization and perhaps the planet Earth, if
we are not careful. Thus, we discuss some
aspect of energy as an introduction to
nuclear technology.
Energy plays an important part
And it’s used in all this work;
Energy, yest energy with power so great,
A kind that cannot shirk.
If the farmer had not this energy,
He would be at a loss,
But it’s sad to think, this energy
Belongs to a little brown horse.
A school verse by Richard Feynman
a Nobel laureate for physics
In this chapter, we are exploring the
following questions.

What is energy?
What are the forms of energy?
How does energy convert from one form to another?

How can amounts of energy be measured or determined?
How does energy cause changes?
How does energy behave?

Why does it rain or snow?
How is energy related to rain or snow?
1
Mechanical Work and Heat as Forms of Energy
Temperature scales were invented to compare hotness or coldness, and their invention enabled
us to measure quantities of heat. During the same period when temperature scales were
invented, Newtonian physics had defined mechanical work, but a long time elapsed before
James P. Joule (1818-1889) recognized that heat and mechanical work were inter-convertible.
Then inter-convertibility between mechanical work and heat led to the concept of energy,
which was coined to represent all elusive driving forces of changes
Mechanical Work
Mechanical work, is defined in Newtonian physics, using distance, mass and force.
Distance and mass are basic quantities, measured by comparing with the standard meter and
kilogram. The force, however, is an elusive concept that is defined in terms of mass and
distance (more precisely acceleration). Mechanical work is discussed fully in Newtonian
mechanics, and only a brief review is given here.



What are mass and distance?
How are masses and distances measured,
and in what (SI or other) units?
Newtonian mechanics
Strictly speaking, Newtonian mechanics is valid only
in a coordinate system with its origin at the center of
the solar system.
What is force?
How a force can be delivered?
What units are used for force?
How much force is 1 N?
The 1st law defines mass m as a measure of inertia.
The 2nd law gives the acceleration a imparted to a
body by a force F
a=F/m
What is mechanical work?
What are the units for mechanical work?
The SI units for mass and distance are kilogram
(kg) and meter (m) respectively. They are
measured by comparing with the standard
meter stick and kg mass. Please note the
following quantities and units.
Both F and a are vectors, having magnitudes and
directions. (Newton = kg-m/s2)
The 3rd law states that actions of two bodies upon
each other are equal, but opposite.
Force, F, is the ability to accelerate (or decelerate) a mass m according to the law of motion,
F = m a,
where a is the acceleration. A force with the ability to accelerate a 1-kg mass by 1 m/s2 is 1
Newton (N), which is the SI unit for force. Its basic dimensions are kg-m/s2. A Newton is the
gravitational pull on a 102-g mass.
Forces exist in various forms: gravitational, electromagnetic, strong interaction (between
nucleons), and weak interaction are four basic types of forces matter exerts over matter, and
force can be delivered by mechanical (springs), chemical (bonding) and physical (steam
2
expansion) means. In chemistry, the inter-atomic forces within a molecule holding atoms
together are chemical bonds. Weak intermolecular forces are generally called Van der Waal’s
forces or London dispersion forces, but strong intermolecular forces include hydrogen
bonding, ionic and dipole attractions.
Without the concept of force, there is no means of comparing masses and vice versa.
Concepts of force and mass are mutually dependent. However, on Earth, we always associate
mass with weight. A 70-kg person weighing 686 N on Earth weighs 289 N on the moon while
there is no change in mass. In a weightless region, everybody is equal (in weight)!
Force that causes no change of state does no
mechanical work. Gravity does no work on any
stationary object. A force (F) acting on an object,
causing it to move a distance (s) in the direction of
the force, does mechanical work (W), and
W=Fs
(J = N m).
A force of 9.8 N pulling an object (1 kg) up by a
distance of 10 m performs 98 Jules of work. The
SI unit for work is Joule (J), which is a
Newton-meter (or 1 kg-m2/s2).
A more elegant definition of work
Mechanical work, W, is a scalar quantity or
state quantity that is defined by a
mathematical dot product of the two
vectors: force, F, and the distance, s.
W (J) = F · s.(N  m)
This is useful if you have the background in
vector geometry and understand the dot
product of vectors.
Work is a state quantity; the same amount of
work is required if the initial and final states are
the same. The length of time or the methods used to raise the weight has nothing to do with
the amount of work done. The unit used for work in the imperial system is foot-pound
whereas erg (dyne-cm) is the unit used in the cgs (centimeter-gram-second) system.
Another definition of work is the distance times the component of the force in the
direction of the distance. Both formulations give the same results.
What happens to the force components that are not in the direction of the displacement? If
we push a strong wall with great strength but the wall does not budge (s = 0), no useful work
is produced; the effort (not work) is completely wasted. When a force is used to pull an object
up a height, it gains potential energy, and when it accelerates an object, it gains kinetic energy.
Skill developing problems:
1. How much work is done to 1.0 L of water when it is pulled from the top of a water fall down by a distance
of 100 m? Gravitational pull is 9.8 m/s2 (Ans. 980 J)
2. A fish with 1-kg mass in water faces a total resistance of 1.0 N. It gains 10 m/s speed over a distance of
1 m of movement. What is the average force exerted by the fish in this movement? (F = 50 N)
3. A sled weighing 50 kg experiences a gravitational force of 490 N. When it is pulled across a frozen lake,
the average force due to friction is 10 N. Calculate the amount of energy required to pull the sled across the
lake for a distance of 10 km. (105 J).
3
Potential and Kinetic Energy
When a force acts upon an object for a distance, the state of the object has changed. The
change in location results in a change in potential energy, and the change in velocity results in
a change in kinetic energy. Although the concept of energy has yet to be defined, these terms
are used loosely because most of you are already familiar with them.

What are potential and kinetic energy,
and how they are evaluated?
Potential energy is the mechanical work stored in a particle or body or system due to location
or height in a force field. In a gravitational force field, g, a mass m kg raised to a height ht, has a
potential energy Ep
Ep = m g ht in Joules (J),
(g = 9.8 m/s2 being gravitational acceleration).
For example, a person weighing 70 kg (154 lb) against a gravitational force of m g walking up a
set of stairs for a total height of 10 m would acquire a potential energy of
Ep = 70 x 9.8 x 10 kg-m2/s2 (or J)
= 6860 J
= 6.86 kJ
Kinetic energy is the mechanical work possessed by a particle or body by virtue of its motion.
An object with mass m moving at a speed of v has the kinetic energy (Ek) of
Ek = (1/2) m v2
For example, a 70 kg mass moving at 14 m/s has a kinetic energy of
Ek = (1/2) 70 kg x 142 (m/s)2
= 6860 J
It can be shown that an object falling a distance of 10 m in a field of 9.8 m/s2 shall gain a
speed of 14 m/s. In this process, all potential energy is converted to kinetic energy (Ep = Ek)
Skill developing problems:
1. A cat jumps down a 5-m cliff with no hesitation, but a dog doing the same may suffer serious injury, why?
2. How can the kinetic energy be stored and recovered during the braking process of a moving automobile?
3. During a marathon race, should a runner keep the same speed, run faster, or run slower on an up hill
stretch of the track? What about the down hill stretch of the road?
4. A dog and a cat weighing 10.0 and 0.5 kg respectively had a free fall (no air resistance) from a cliff of 10
m in height. (1) Calculate the kinetic energies when they are just about to hit the ground. (2) Calculate the
ratio of kinetic energy of the dog to that of the cat. (g = 9.8 m/s2) (Hint: K.E. = P.E. = mgh; Ans:
Ek.(dog) = 990 J; ratio = 20).
4
Temperature Scales
You have used the Fahrenheit (F), Celsius (C ), and
Kelvin (K) temperature scales, and know how to
convert from one to another, but you might not be able
to explain the principle of temperature measurement.
 Why do we need temperature scales
and how did these scales develop?

What is the principle used to measure temperature?

How have temperature scales affected the
development of science and technology?

What is 0K in the Celsius and Fahrenheit scales?
N
F
C
K
212
100
373.15
12
98
37
310
0
32
0
273.15
-40
233.15
-40
Newton (N), Fahrenheit (F), Celsius ( C), and
Kelvin (K) temperature scales.
Sensation for hot and cold is instinct for humans and
other animals. However, sensation is subjective and
circumstantial. For example, if you place one hand in
1
cold and one hand in warm water for a while, and then put both hands in the same bucket of
water, the two hands feel differently.
Peking man used fire about 500,000 years ago. Humans have recognized heat and fire at the
dawn of civilization. The objective of fire at that time was to provide warmth and illumination,
since cooking was not an art until much later. Despite the lack of thermometers, people in
Egypt, Mesopotamia, India, and China used fire to produce metals, and to work copper, lead,
tin and iron into tools. Fire played such an important role in early civilization that Plato (427347 BC) thought it was one of four primal substances from which all other matter was derived.
During the 2nd century, the Greek physician Galen suggested a temperature scale based on
boiling water and ice. Arab and Latin physicians developed a scale of 0-4 degrees for hot and
cold depending on human senses. In 1688, the French physician Guillaume Amontons
proposed to measure hotness and coldness by the variation in pressure of a fixed amount of
gas contained in a constant volume. He defined absolute zero when the pressure is zero, and
used a tube of mercury to measure the pressure. In 1701, Sir Isaac Newton (1643-1727)
suggested 0 degrees for ice and 12 degrees for the human body as a temperature scale. G.D.
Fahrenheit (1686-1736) proposed a temperature scale in 1714. The scale used a salt-water-ice
mixture as a reference for 0, and the human body as 96 degrees. This scale had many more
divisions than the one proposed by Newton, and the freezing point and boiling point of water
was calibrated to be 32 and 212 degrees respectively. This finer scale greatly improved the
precision of temperature measurements. The centigrade (Celsius) scale was proposed by the
Anders Celsius (1701-1744) ten years after Fahrenheit’s proposal.
5
Using a temperature scale, Jacques-A.C. Charles
(1746-1823) and Joseph L. Gay-Lussac (17781850) studied the expansion of gases. They
found that hydrogen and most other gases
expanded 1/273 of their volumes at 0oC per
degree C increase. This is known as the CharlesGay-Lussac law of gases. In general, when the
A thermocouple consists of two different metals,
pressure is held constant, the volume of a gas
which give rise to a voltage depending on the
increases the same amount as the temperature
temperature of their junction.
increases each degree. William Thomson (18241907, known as Lord Kelvin of Glasgow) came
up with the absolute temperature scale (K after
Kelvin) in 1848 in conjunction with the Charles-Gay-Lussac law. Absolute zero corresponds to
-273oC, and at this temperature, no heat can be extracted from the system any more.
Usually, thermometers use gases or liquids that expand upon heating. However, extreme low
or high temperature measurements require instruments other than ordinary thermometers. For
example, temperatures between -183 and 630oC can be determined from the electric
conductance of platinum. In 1821, Thomas J. Seebeck (1770-1831) discovered that when the
junctions of two dissimilar metals were placed in different temperatures, the circuit generated
an electric potential (voltage). Such devices, called thermal couples, have been developed for
temperature measurements. Spectra of light emitted by hot objects have also been used to
determine their temperatures. Temperature measurements are an important part of scientific
research and technological development.
Skill developing problems:
Two bodies each equal in temperature to a
1. On the Newton’s temperature scale of 0 for ice and water
third body are equal in temperature to
mixture and 12 for the human body temperature, what is the
each other.
boiling point of water? What is the reading corresponding to
Maxwell (19th century, now known
absolute zero? (-88.5 N)
as the 0th law of thermodynamics)
2. What is 0 K in the Celsius and Fahrenheit temperature
scales? (-459.7 F)
3. What is the temperature at the surface of the Sun? (a few million degrees Kelvin).
Heat
Like work, heat is also an elusive quantity. Intuitively, we know that an object containing a lot
of heat is hot, but the description is inadequate. After having invented and used temperature
scales, humans wanted to better understand heat.

What is heat and how does it flow?
How did our interpretation of heat evolve?
What is the relationship or difference between heat and temperature?
6

How is heat stored in an object or a system?
What is the meaning of heat capacity?
How does heat differ from chemical
energy?
In 1760, Joseph Black (1728-1799) recognized
that "heat is evidently not passive; it is an expansive
fluid, which dilates in consequence of the repulsion
subsisting among its own particles”. He considered
this caloric fluid to be indestructible and to be
accumulated when matter was heated.
Comparing heat with a fluid was a good step in
Is heat a fluid like water?
our effort to understand heat. Black
differentiates heat from hotness. Like mass and
2 quantity. Thus, heat, volume, and mass
volume that describe amounts, heat is a typical additive
are extensive properties. In contrast, temperature is not a quantity measured in amount; it is a
measure of the type called intensive property, as are pressure, density, heat capacity, latent
heat of melting, latent heat of evaporation, etc.
With the help of a temperature scale and his caloric (weightless fluid) theory, Black defined
heat capacity as the amount of calorie required for raising or lowering the temperature of a body by 1o.
Furthermore, he realized latent heat of melting of a solid such as ice. He demonstrated that a
fixed amount of ice always requires the same quantity of heat to melt. Now, we know that a
fixed quantity of liquid also requires a certain amount of heat to evaporate. Heat capacity,
latent heat of melting and heat of evaporation are also intensive properties. The caloric theory
was believed for more than 100 years, until the middle of the 19th century, when the concept
that heat was a fluid-like quantity could not explain phenomena related to mechanical work,
radiation, and chemical reactions.
As an extensive property, the amount of heat must be precisely described. An amount of heat
required to raise the temperature of 1.00 g of water from 288.5 to 289.5 K is defined as
1.00 calorie. This strict definition hints that the heat capacity for water changes with
temperature, even between freezing point and boiling point. On average, the heat capacity for
water is 1.00 cal g-1 K-1, whereas the heat capacity for ice is only 0.50 cal g-1 K-1.
Skill developing problems:
1. The caloric fluid concept explains what aspect of heat, but cannot explain what properties of heat?
2. On average, 1 cal. is required to raise the temperature of 1 mL water by 1 K. How many calories are
required to warm up a cup (250 mL) of water (for tea) from 288 K to 363 K? (18.8 kcal.)
3. The heat of fusion for ice is 80 cal per gram (or 6.02 kJ/mole) and the heat of vaporization for water is
540 cal per gram (or 40.67 kJ/mol). The heat capacities for water and ice are 1.00 and 0.50 cal g–1 K–1
respectively. How much heat in kcal and kJ is required to convert one mole (18 g) of ice from 263 to 373
K. (Ans. 13.1 kcal or 54.6 kJ).
7
Inter-conversion of heat and
mechanical work
Thermometer
That mechanical work can be converted to heat
was discovered unexpectedly.

Why is heat not a fluid?

What is energy?
Why is the concept of energy useful?
How is energy stored in a body of material?

When energy is transferred from one place to
another, what phenomena do you observe?
mgh
Joules experiment demonstrated the
generation of heat by mechanical means.
Sir Benjamin Thompson (1753-1814) used horseturned machines for boring brass into cannons in
the military arsenal at Munich. He observed the brass getting hot in this process, and
Figure 3
concluded that heat is hardly a substance or fluid, but is generated by mechanical work done to the system.
He recognized that heat is furnished as long as parts in it persisted moving. He calculated the
equivalence between the heat generated and the mechanical work done to the system, and
James P. Joule (1818-1889) who studied under J. Dalton, refined the experiments by measuring
the temperature rise in water churned by a paddle driven by a descending weight. These
experiments showed that heat, and mechanical work, are inter-convertible.
In 1852, Joule and Thomson discovered that temperatures of gases decrease when they are
expanded. During expansions, heat is converted to mechanical work.
Since heat and mechanical work are inter-convertible, they should be treated as a single entity.
This entity was called effort, living force, and travail, before the term energy was accepted. This
term was coined by Thomas Young (1773-1829) in 1807, from the Greek words energia; en
meaning in, and ergon, work. Since then, the term energy is used to mean mechanical work (or
simply work), heat, and other forms of energy.
Energy can be quantified, but its meaning is elusive. Quantities of energy are expressed in
various units depending on their forms. The basic or SI units are derived from those of mass
(kg), length (m), and time (s). Most of you are familiar with various forms of energy, but a
review is given in the next section.
To speak of the heat or work in a body is improper, because heat and work are really energy
being transferred. Energy stored in a body is neither heat nor work. Upon absorption of
heat, molecules or atoms in materials move faster, converting from solid to liquid or from
liquid to gas. In 1738, Daniel Bernoulli (1700-1782) proposed that the motion of gas molecules
gave rise to pressure. Kinetic energies of gases are proportional to their temperature. Once
absorbed, the nature of heat has changed. Rudolf J.E. Clausius (1822-1888), James Clerk
Maxwell (1831-1879), W. Thomson, and Ludwig E. Boltzmann (1844-1906), studied the
8
relationship between temperature and energy of molecular motion. Many elegant theories have
been developed as a result.
Heat is energy being transferred via a medium from a source of higher temperature to a target
of lower temperature. Temperature is a measure of relative potential of energy. Molecules and
atoms in a body of material rotate, vibrate, or move, and hence possess energy. When residing
in a body of material, you probably don’t call it heat until it flows.
Heat, light, mechanical and electric work, and sound are actually forms of energy in
transmission. Heat is energy transmitted by conduction and convection. Light
(electromagnetic radiation) is energy transmitted via no medium. Mechanical and electrical
works require the transmission of objects or electric charges, whereas sound is the result of
energy transmission by a mechanical process.
In terms of nuclear technology, we often deal with high-energy subatomic particles. Energy of
these particles is stored as kinetic energy. Temperatures of a collection of particles are related
to their average speed, and we shall discuss these aspects in various chapters later.
Skill developing problems:
1. What is energy? Give an example to show how heat can be converted to mechanical work. Identify at least
5 different phenomena caused by energy.
2. Describe the nature of heat and work as energy in transition.
3. How is energy of molecular motion related to temperature?
9
Other Forms of Energy
As mentioned in the last section, heat, and mechanical work are two forms of energy. Other
forms are light, electric work, sound, chemical energy, and nuclear energy. Some of these
forms are energy in transmission, and some are hard to recognize as energy. We review some
fundamentals of these forms of energy in the following sections.
Electric Energy
Most technologies, including nuclear technology,
involve electric energy. For example, kinetic
energies subatomic particles are often expressed in
electron volts, eV. Having ability to evaluate
electric energy is important.

How much energy is 1 eV, 1 MeV or 1 GeV?
Electric energy, E, possessed by a charge q
experiencing a voltage V, is the product of q and
V.
E =Vq
+
+
+
+
+
+
+
-
Electric field
(units: J = V C)
The SI units are Joule (J), volt (V), and coulomb (
C) for E, V and q respectively. An electric charge
experiences the electric field as a mass does the
gravitational field.
The power P of output or input in a circuit is,
P = V q /t = V i
Gravitational field
Similarity between pushing a charged particle against
an electric field and pushing a weight against a
gravitational field.
in watt
where t represents time, and i = q/t is the current. The SI units for i, is ampere (C s–1).
The voltage drop V in a circuit is the product of i (in A) and resistance R (in Ohms, ),
V =iR
(Ohm’s law)
Thus, we can re-write the power as
P = R i2
(Joule’s law)
For example, the power delivered by 12 volt battery constantly discharging 50 amperes per
second is 50 C/s x 12 V = 600 J/s (or 600 watts).

Power is rate of energy transfer, or energy input or output per unit time. A section is devoted to it later.
10
In nuclear technology, a commonly used energy unit is the electron volt, eV. The smallest
amount of charge detected is the amount of charge of electron. The charge of an electron is
1.60219x10-19 C. Because the electron is negatively charged, 1 eV is the amount of energy
(1.60219x10-19 J) to lower the electron by 1 volt. When an electron is accelerated by a 1000-V,
it gains 1000 eV or 1 keV, and when accelerated by 1,000,000 V, it gains 1,000,000 eV or 1
MeV. For high energy, 1 GeV = 109 eV.
Units keV and MeV are often used to describe energy of subatomic particles such as electrons,
protons, and neutrons, as well as photons in the X-ray or gamma region. Modern accelerators
such as the DESY (Deutsches Elektronen Synchrotron) in Hamburg, Germany and the
accelerator at Cornell University have accelerated protons to energies of 6.5 and 12 GeV
respectively.
Skill developing problems:
1. What are the advantages and disadvantages of
Joule and Electric Energy
building dams for electric power generation?
2. How much energy is delivered by a battery operating In 1840, Joule (a 22-year old Manchester
at 12.0 V in a discharge of 150 C, when you start brewer) learned that the amount of heat
the engine? Express this amount of energy in J, cal, produced per unit time (power P) by the flow
and eV. (W = 1800 J)
of an electrical current was proportional to the
resistance ( R) of the conductor, and to the
3. What is the resistance for a heating element
operating 0.1 watts when V = 1.5 V? (Ans. P = square of the current (i) flowing (Joule’s law).
Vi = V 2 / R; R = 22.5 )
P = R i2
4. What is the current for a heating element operating
Since i = q / t, and V = i R
at 60 watts and 12 V (DC)? How many electrons
pass through per second? (Current = 5 A, No.
P = Vi
of electrons = 3.3 x 1019 e/s).
E=Pt
5. A 12-V storage battery delivers 100 A while
starting an engine. Calculate the power delivered by Combined with the discovery that mechanical
the battery. How many electrons per second pass the work also generate heat, he had quantified
electric energy in terms of heat and work.
terminal? How much energy does each electron
20
deliver? (Power = 1200 watt; 6.24 x 10 electron per second; each electron delivers 12 eV;
6.24 x 1020 x 12 eV = 1200 J energy)
6. Describe the conversion between various forms of energy when you start an engine with a battery.
7. A stove operating at 1000 watt takes 10 minutes to heat 1 L of water from 20 to 100o C. Calculate the
energy (in J and cal) consumption and efficiency. (Ans. 143 kcal, 56%).
8. A microwave oven operating at 600 watt takes 2 minutes to warm up 200 mL of water from 20 to 90oC.
Calculate the efficiency of the process. (Ans. 81%)
11
The Electromagnetic Radiation Spectrum
Electromagnetic radiation is a form of energy transmitted in the form of waves due to an
oscillation of electric and magnetic fields travelling away from a source. Visible light is an
example of the electromagnetic
radiation. Electromagnetic waves travel
The Electromagnetic Radiation
at constant speed in vacuum, and they
Spectrum
have characteristic wavelengths or
frequencies. Classified by frequencies,
Long wavelength radio > 600 m
the electromagnetic radiation
Broadcast radio band 600 - 200 m
spectrum consists of radio waves, TV
signals, microwaves, infrared, visible
Short wavelength radio 200 m - 0.1 mm
light, ultraviolet, X-rays, and gamma
Infrared 0.1 - 0.0007 mm
rays.


VISIBLE
Does light consist of waves,
particles or both?
0.7 - 0.4 um
Ultraviolet 0.4 um - 1 nm
X-rays 1 nm - 0.1 pm
What phenomena of light beams
demonstrate wave properties? What
type of waves are light?
How energy is transmitted by light?
Gamma rays 0.1 nm

What is the speed of light?
How can this speed or velocity be measured?

Describe differences and similarities among radio waves, TV signals, microwave, infrared,
visible light, ultraviolet, X-rays, and gamma rays?
In 1666, Newton decomposed white light into a rainbow spectrum of red, orange, yellow,
green, blue and violet using a prism, and using a second prism he combined the rainbow
spectrum into a white beam. His experiments separated light into components, but whether
light beams consist of particles or waves was not yet resolved.
Most phenomena of light can be explained by considering
light as particles, except the color patterns formed on soap
bubbles or thin oil films called Newton rings. This puzzles
was solved by Thomas Young (1773-1829) who assumed
light as a wave, and explained the color patterns as due to
interference, a property observed for only waves not
particles. Since then, all phenomena (reflection, refraction,
and diffraction) of light have been explained by the
electromagnetic wave theory, by which light is the
transfer of energy by wave actions without a medium.
A color pattern seen in an oil film
The universal speed of light was first calculated from the time difference required for the orbit
of Jupiter’s moons when the earth was moving towards or away from the Jupiter, by the
12
Danish astronomer Olaf Roemer. Further refinements give the speed of light as 299,792,458
(or 3x108) m/s.
The radiation spectrum covers radio waves used in broadcast, microwaves used in
communication, infrared radiation usually considered as heat, visible light of various colors,
ultraviolet light, X-rays, and gamma rays. All have wide ranges of wavelengths, which decreases
in the order given above. With the universal speed (c = 3x108 m/s) and wavelengths, , of
waves in the radiation spectrum measured, their frequencies, , can be evaluated,
 = c/.
The product of frequency and wavelength equals to the speed or velocity of light,  = c.
The wave number is the number of waves per unit length (m or cm), and it is the reciprocal
of wavelength,  = 1/.
The energy, E, transmitted by electromagnetic radiation is proportional to its frequency , or
its wave number  according to Max Planck* .


E = h , (Planck’s equation)
= h c/
 = h c 
where h = 6.62619 x 10-34 J s is the Planck constant, and h c = 1.9865 x 10-25 J m.
*
Max K.E.L. Planck (1858-1947) studied the distribution of radiation energy of black bodies over the entire
range of wavelengths at various temperatures. A black body is a perfect absorber and radiator of
electromagnetic radiation. John William Strutt (1842-1919, known as Lord Rayleigh) derived a law that
agreed with the long wavelength range. Wilhelm Wien (1864-1928, 1911 physics Nobel prize) gave the
displacement law for the short wavelength range. However, there was no satisfactory theory to deal with the
entire spectrum. In order to give a formula explaining the entire spectrum for all temperatures, Planck
postulated that light was emitted as small bundles of energy called quanta, whose energy E is
proportional to the frequency of light 
13
The equation was an assumption made by Planck . He assumed that light is emitted as
small bundles of energy E called quanta.
Light beams consist of many photons, which
I
Rayleigh’s
are elements of electromagnetic radiation.
N
Prediction
T
The amount of energy to be transmitted by
E
Experimental curve
radiation determines the photon frequency.
N
and Planck’s prediction
Using his assumption, the specific heat of
S
substances, Stoke’s law of phosphorescence
I
and fluorescence phenomena, and black body
T
Wien’s Law
Y
radiation are explained. Furthermore, the
assumption was confirmed by Einstein’s
famous photoelectric experiment.
Frequency
The wavelength of a typical red light is 640
nm (1 nm = 10-9 m). Its frequency is

Prediction using classical electromagnetic-wave theory
and experimental equilibrium radiation density of perfect
absorber.
 = c / 6.4 x 10-7
= 3 x 108 (m/s) / (6.4 x 10-7 m)
= 4.69 x 1014 /s (or Hz)
Thus, the energy of the red light photon is
E = h ,
= 6.6256 x 10-34 J s x 4.69 x 1014 /s
= 3.1 x 10-19 J (1 eV / 1.6 x 10-19 J)
= 1.9 eV per photon
Kinetic energy
of electron
The energy of a typical green light photon with
wavelength 500 nm has more energy than a red
light photon,
E = h c/
= 1.9865 x 10-25 (J m)/ 5.0 x 10-7 (m)
= 4.0 x 10-19 J (1 eV / 1.6 x 10-19 J)
= 2.5 eV per photon
Threshold
Frequency
Kinetic energy of electrons liberated from metal
surface as a function of frequency.
The wavelengths of X-rays are shorter than those of visible light. A photon of typical X-ray
with a wavelength 0.1 nm has 5000 times more energy than that of green light,
E=hc/
= 1.9865 x 10-25 (J m) / 1.0 x 10-10 m

Planck received the Nobel Prize for physics (1918) after his assumption was confirmed using photo-electric
effect experiments by Albert Einstein (1879-1955). Experiments showed that electrons could be liberated from
a metal surface by light of certain frequency (threshold) or higher, indicating that the light was proportional to
the frequency, as proposed by Planck. Einstein further showed that the kinetic energy of the liberated electron
is proportional to the frequency of the photons used. For his experiment, Einstein received the Nobel prize in
1919.
14
= 2.0 x 10-15 J (1 eV / 1.6 x 10-19 J)
= 12500 eV or 12.5 keV per photon
The total amount of energy transmitted in a light beam is the sum of all photon energies.
Light as a form of energy is best illustrated
Spontaneous decay
by LASER, acronym for Light Amplification
by Stimulated Emission of Radiation. When
Green
a rod of chosen material absorbs light energy,
Stimulated decay,
photons
the material is raised to a higher energy state.
Red laser
The ends of the rod are polished flat, parallel,
and coated with mirrors to reflect light. Thus,
Partial mirror
Mirror
the emitted light travels back and forth in the
rod stimulating further emission. The partial
mirror on one end of the rod allows some
Red laser
light to pass through, and the emission is
called LASER, which is a strong
Green pumping light
monochromatic, parallel, and coherent light
beam. The rod material can be a solid, liquid,
solution, or gas. You already know that
An oversimplified energy level diagram (for chromium
ion in ruby) and laser generation device.
energy of LASER beams have been used for
surgery to vaporize unwanted material.
LASERS are also employed in nuclear fusion technology.
Review Questions:
Key Constants and Formulas
1. Visible red light has a wavelength of 700 nm (1
nanometer = 10-9 m). Calculate the frequency, the
Planck’s constant, h = 6.6256 x 10-34 (J s)
photon energy, and the wave number (/cm).(Ans.
x 108 m/s
Frequency = 4.23 x 1014 Hz, E = 2.8 x 10-19 Velocity of light, c = 2.997925
h c = 1.9865 x 10-25 J m
J = 1.8 eV, wave number = 1.43 x 106
Wave length, wave number  = 1/
wave/m = 14300 wave/cm).
Frequency:  = c/
2. Calculate the frequency, the wavelength, and the
EnergyE = h  = h c /  = h c 
wave number (/cm) of a photon with energy 0.5
MeV. (frequency=1.21e20 Hz; wavelength
=2.48e-12 m; wave number= 4.0e11 per m)
3. Photons in which of the following types have the highest energy: infrared, ultraviolet, X-ray, or microwave?
4. An argon laser has a wavelength of 514.5 nm; calculate the energy of its photon. (E = 3.86e-19 J)
5. The threshold of most metals is between 2 eV (for cesium) and 5 eV (for platinum). Calculate wavelengths
of photons corresponding to these threshold energies. (Please fully explain the photoelectric effect.)
15
Chemical Energy
A substance possesses chemical energy by virtue of its
composition, chemical bonding, and state. The absolute
amount of chemical energy in a substance is not a measurable
quantity, neither is the quantity useful. All chemical reactions
are accompanied by a change of energy. An endoergic
reaction absorbs energy in the procedure. For example the
electrolysis of water into hydrogen and oxygen is an endoergic
Ice in water is a cool drink!
reaction. Electric energy is used in the process. An exoergic
reaction releases energy, which may be in the form of heat or
light or both (burning of a gas), or in the form of electric
energy (reactions in a battery). Endoergic and exoergic reactions are often called endothermic
and exothermic reactions respectively. The terms endoergic and exoergic emphasize the
energy concept whereas endothermic and exothermic refers to heat.
The study of absorption, emission, transformation and conversion of heat is known as
thermodynamics, which is studied by scientists and engineers. In thermochemistry, elements
at standard temperature (273 K) and pressure (101.3 kPa) are referred to as a zero-level of
energy for reference. Energy levels (or contents) of their compounds are compared to these
standards.

What are endoergic, exoergic, endothermic, or exothermic reactions?

How is energy stored in material by virtue of state, chemical composition, and chemical
bonding?

More new terms such as energy (or enthalpy) of fusion, energy (enthalpy) of
vaporization, energy (enthalpy) of reaction etc. are introduced. What are these
quantities and what are their amounts for a particular material? Where can you find the
information?
To illustrate the various chemical energy, let us concentrate on 36 g (2 moles H2O, or 2H2O in
chemical formulation) of water at various stages. When placed in a colder environment, heat
can be extracted from ice at 273 K. So, ice at 273 K is not the lowest energy point yet.
If the ice at 273 K is heated, temperature will not increase until all the ice melts. Under ideal
conditions, experiments show that 12 kJ will be required to melt 36 g ice. In other words, at
the same temperature, 36 g water contains 12 kJ more energy than ice at the same temperature.
This amount of energy is called enthalpy of fusion.
16
When water is heated, energy content increases.
Since the heat capacity of water is 4.184 J/K g,
15 kJ (= 36*100 * 4.184 J) is required to bring
36 g water from 273 to 373 K. By absorbing
heat, the energy content of water increases.
4H + 2O
Enthalpy of vaporization is the energy
required to convert a liquid to a gas at the same
temperature. For 36 g of water, 81 kJ is
required. Thus, energy content of the steam is
higher than that of water at the same
temperature.
Water vapor and a mixture of hydrogen and
oxygen are gases, but when the gases in the
mixture react, the energy or enthalpy of
reaction will be released as light and heat.
1469 kJ, bond energy
2H2 + O2
The mixture of hydrogen and oxygen gases
consists of diatomic molecules. Bond energies
(971 kJ for 4 g of H2, and 498 kJ for 32 g of O2)
are required to dissociate the hydrogen and
oxygen molecules. Of course, mono-atomic
gases mixture releases more energy than does
diatomic gases mixture in their reactions to
produce water.
484 kJ, energy of
reaction
2H2O(g)373K
81 kJ, energy of
vaporization
2H2O(l)373K
15 kJ, heat
2H2O(l)273K
2H2O(s)273K
12 kJ, energy of fusion
There are other types of energies in chemical
process, but these are beyond the scope of this
book. You are introduced to some interesting
aspect of thermodynamics in this section, and
you may find more thermodynamic properties (or data) for a substance in for example the
CRC Handbook of Chemistry and Physics.
Despite huge amounts of chemical energy stored in various substances, energies released have
not given measurable changes to mass of the systems or bodies of substance (see
Mass and Energy for further details). For chemical and physical reactions, therefore, total mass
changes before and after reactions are not measurable. Thus, mass and energy are treated
separately, and they are said to be conserved individually or independent of each other.
The energy contents of food have been tabulated giving the unit calorie. However, the ‘calorie’
used by dieters in the past was really a ‘kilo-calorie’ as defined earlier.
1 food cal = 1 kcal = 4.184 kJ.
(in old dietary literature, but new literature uses kJ.)
17
The major food energy is derived from
proteins, fats and starches (carbohydrates).
Their heats of combustion and their
physiological energy as food are slightly
different, because not all ingested food is
absorbed and utilized. Most food is a
combination of proteins, fats and starches plus
other nutrients such as water, vitamins and
minerals. However, flavor, taste, and sensation
are more important than nutrition to most of
us.
Review Questions:
Energy Content (kcal/g) of Major Food
Food
Heat of
combustion
Protein
cheese
beef
Fat
butter
Carbohydrates
potatoes
sugar
5.4
9.3
4.1
Physiological
energy
4
4
3
9
8
4
0.7
4
1. What are endoergic and exoergic reactions or processes? Give some examples for each.
2. Define energy of reaction, energy of formation, energy of phase transition, and bond energy.
3. Use the bond energies H-H, 436; O=O, 498; H-O-H, 498*2 J/mol to show that the energy of reaction
for the reaction 2 H2 + O2 = 2 H2O is 622 kJ for each mole of O2 reacted. Discuss your results.
4. Experimental data indicate that burning 2.3 g of gasoline releases 110 kJ energy and the density of
gasoline is 0.60 g/mL. Calculate the amount of energy released from burning 1.0 L (liter) of gasoline.
(Ans: 28,696 kJ)
Energy and Mass Equivalence
The kinetic energy gained by a particle increases
its mass according to the special theory of relativity
developed by Einstein in 1905. He derived an
equation to calculate the relativistic mass m of a
particle from the rest mass mo by the equation:
m =
mo
v 2
1 - ( )
c
where v and c are the velocity of the particle and
the velocity of light (3 x 108 m/s) respectively.

Universal speed
299,792,458 m/s
All electromagnetic radiation travel in empty space at
the same universal speed.
Newtonian physics could not explain the phenomena related to the absorption of light by molecules or atoms,
and shortcomings were found in motion of high energy particles. In an effort to find the elementary foundations of
an adequate theory of matter, radiation, and electricity, and in the mean time stimulated by scientists H.A. Lorentz, M.
Planck, A. Summerfeld, J. Stark and W. Wien, Einstein (1905) abandoned the concept of a universal or absolute
space and time on which Newtonian kinematics was based. Einstein considered Newton’s laws of motion in
relative coordinate systems or spaces, and further accepted the 1887 experimental result of A.A. Michelson and
E.W. Morley that velocity of light is always the same, regardless of the motion state of the emitter.
Incorporating these new concepts of space and time into the fundamental principles of conservation of energy
and momentum, he unveiled a new field in 1905 called special theory of relativity, which arrived at some startling
results.
18
The consequence of his theory is far reaching, and all atomic and nuclear phenomena require
some parts of his theory to be explained adequately.

What is the significance of Einstein’s special theory of relativity?

How can the increases in mass of a particle be measured?
What is the mass increase for a particle moving at 1% of the velocity of light?

Calculate the mass equivalence of 1 J and the energy equivalence of 1 g.
Einstein (1909) further showed that the relativistic mass, m, of a particle exceeds its rest mass
mo (m = m - mo). The increase in kinetic energy E and increase in mass are related by a
simple equation:
E = m c 2
which is often written as E = m c 2 by dropping the symbol of difference, . Mass can be
converted to energy under the right conditions. This equation is the expression of the principle of the
energy mass equivalence (der Ausdruck des Prinzipes der Äquivalenz von Masse und Energie), m
being the mass equivalence of energy, and E being the energy equivalence of mass. For highenergy particles such as electrons and protons moving at the velocities close to that of light,
the masses increase agree with results calculated by this equation.
No particle can be accelerated to a velocity equal to or greater than that of light, according to
the relativistic mass equation, because its mass will be infinity when its velocity is the same as
the speed of light (v = c) unless the rest mass, mo, is zero. As its kinetic energy increases, so
does the mass of a particle. Note that the increase of a particle's mass is a continuous function,
in contrast to energy states of a microscopic system being discrete according to Planck’s
assumption.
Since energy and mass are equivalent, they must be considered together in the
law of conservation of energy. As mentioned earlier, only small amounts of energy is involved
in chemical or physical changes, mass and energy are conserved independent of each other.
The equation E = m c 2 permits the calculation of the total or absolute amount of energy for a
mass m, but not all energy is available for doing work. The lowest mass of a particle is called
ground state, but several excited states might be stable for an indefinite period.
For chemical reactions, the changes in mass due to release of energy are minute, undetectable.
For example, when 2 g hydrogen reacts with 16 g oxygen to form 18 g water vapor, 242 kJ is
released,
H2(g) + ½ O2(g) = H2O (g) + 242000 J
The mass equivalence of 241800 J is (= 241800/c2) 2.7 x 10-12 kg or about 3 nanograms, which
was lost. Three nanograms are insignificant in 18 grams even on the most sensitive chemical
balance.
19
In reactions involving nuclei, the amount of energy is relatively large. In nuclear reactions, the
energy put into or released from a system is so large that the mass changes must be accounted
for.
Since mass and energy are equivalent, the mass is
sometimes expressed in terms of energy. This is
particularly true for the masses of nuclei or atoms. The
atomic mass unit (amu) is equivalent to 931.478 MeV.
The energy equivalence of the rest mass of an electron is
0.511006 MeV. As an exercise confirm these values by
calculation.
An amu is defined as 1/12th of the mass
of a 12C atom, and 1 k mol 12C = 12 kg
1 amu = (12 kg/k mol)/12
= (1 kg/k mol)/(6.022x1026k
mol)
= 1.66x10-27 kg
Now, let us consider the fusion of deuterium, D, and tritium, T, in the formation of helium
(He) with a neutron as the by-product. The reaction is given below, and the masses (in amu)
for the particles are given below their symbols:
Mass (amu):
D +
2.01400
T
=
3.01605
He +
4.00260
n
+
1.008665
Energy
0.01878
Since the sum, 5.03005, of masses of D and T is greater than the sum, 5.011265, of masses of
He and n by 0.01878 amu, the energy released in this reaction is equivalent to 0.01878 amu or
17.5 Mev per He atom formed. When the unit amu is used, the weights given for the above
equation are for each particle, not for a mole of particles as indicated in ordinary chemical
reactions.
In units familiar to you, fusion of 2.01400 g deuterium and 3.01605 g tritium (total 5.03005 g)
to give 4.00260 g helium and 1.008665 g neutrons (total 5.011265 g) has a loss of 0.01878 g.
This amount will be measurable, and the energy giving off, E, can be calculated,
E = 0.01878 x 10-3 kg (3 x 108 m/s)2
= 1.69 x 1012 J/mol,
This is a large amount of energy! If this is the potential energy of a large automobile weighing
1000 kg at a height ht against a constant gravitational field g, the height ht is,
ht =
=
=
=
=
=
1.69 x 1012 J / m g
{1.69 x 1012 (Newton m)}/ {1000 kg x 9.8 m s-2}
{1.69 x 1012 (Newton m)}/ {9.8 x 103 Newton}
1.72 x 108 m
1.72 x 105 km
172000 km
This height is equivalent to a distance around the earth EIGHT times.

The circumference of the earth is about 20,037 km.
20
Review Questions:
Comparison of Energy Released
1. What is the speed of an automobile weighing
E = 2.7 x 10-9 g for
1000 kg if it has a kinetic energy of 8.45
x1011 J. (When about 2 g of D and 3 g 2 g H2 + 16 g O2  18 g H2O;
of T fuse, the amount of energy
E = 0.01878 g for
released sends an automobile
2.01400g D + 3.01605g T  4.00260g He + 1.008665g n
weighing 1000 kg to a speed of 41 km
per second or 148000 km/hr)
2. Calculate the kinetic energy of an automobile weighing 2000 kg when it travels at 120 km/hr. Evaluate
the mass equivalence of its kinetic energy. (1.1x106 J)
3. Calculate the mass equivalence (in kg) of 10000 kJ. (An undetectable amount of 1.1 x 10-10 kg.)
4. Calculate the energy equivalence of 1 amu (= 1.66053 x 10-27 kg), and express the energy in units of J
and MeV. (see text box in the previous page)
5. Calculate the energy equivalence of the mass of an electron (= 9.109558 x 10-31 kg), and express the
energy in units of J and MeV. (see Physical constant for the rest mass of electron)
21
Energy Transfer and Conversion
Various energy forms given in the previous section inter-convert among each other, and
conversion factors, rates of transfer, and the principle of conservation of energy should be
considered in these inter-conversions. Energy can be transmitted via a medium by mechanical
means in the form of sound wave, which is an important mechanism of destruction by nuclear
weapons.
Power  the Rate of Energy Transfer
Power P is the amount of energy transferred
per unit time, and energy E transferred in a
period t is
E = P t.
Power = m g v,
v, pulling velocity
The SI unit for P is watt named after James
Watt* (1 watt = 1 J/s).
mgh
Not only amounts, but also rates of energy
transfer are important considerations. For
example, walking 100 m is very different from
dashing that distance under 10 s. The
difference is power requirement. Sprinters
need very high power output for a short time.
Performing the same amount of work at two different
rates.

Why is a ten-speed bicycle easier to ride than a single-speed bicycle?

A nuclear reactor is rated at 600 megawatt. How much energy is produced per day?
Kilowatt-hour is a commonly used energy unit, not power.
1 kilowatt-hour = 1000 J/s x 3600 s
= 3.6 x 106 J (1 cal / 4.184 J)
= 8.6 x 105 cal or 860 kcal.
This amount of energy enables the heating of 8.6 liters (2.3 US gallon) of water from 0o C to
the boiling temperature if there is no wastage due to heating the air, the furnace etc.
*
At age 29, James Watt (1736-1819) repaired the steam engine Newcomen which was used for pumping water out
of English mines. He then improved the performance of steam engines. In order to compare the effectiveness,
he compared his engines with the strength of an average horse. He defined a housepower (hp) as 550 foot-pounds
per second (about the power of 1½ fine steeds at that time), and this became the standard for rating electric
motors, automobile engines, diesel locomotives, and propeller-driven aircraft engines.
22
The horsepower (hp) is a common unit for power, 1 hp = 745.700 watt = 178.107 cal/s; and 1
watt = 1.34102 x 10-3 hp. Note that a metric horsepower is slightly smaller than a hp, 1 hp =
1.0138 hp(metric). Conversion factors can also be derived from those used for energy.
Review Questions:
9. Assuming the average voltage to be 110 V, what is the current for an appliance rated for 1kilowatt?
(Ideally, calculation of electric energy by alternate current (AC) should be carried out
differently from that of direct current (DC), but you need not to worry about the
complication for AC here. Current = 9.1 A)
1. Convert 1.0 kilowatt-hour to the following units: J, cal, and BTU. (1 BTU = 1055.06 J)
2. An electron is accelerated to give a kinetic energy of 931 MeV in 10-9 s. Calculate the power in this
process.
3. A furnace is rated to give 13700 BTU per hour. Calculate the power in watt.(Ans: 4015 watt)
The Law of Conservation of Energy
Energy, the medium for changes, and money, the medium for exchanges, are abstract and
similar in many ways. Energy conserves, but money (or precisely value) does not. Energy exists
in forms of potential, kinetic, mechanical, electrical, chemical, thermal, geothermal,
electromagnetic radiation, and nuclear (mass equivalent). Energy converts among various
forms without any loss or gain, states the law of conservation of energy. Your money
exists in forms of real estates, jewelry, automobiles, audio and video systems, minerals, energy
providing commodities, etc. Every time you buy, sell or exchange, you think you gain. So does
the other guy. Money (or more precisely value) is not conserved.

Is energy really conserved?
How can you demonstrate that energy is
conserved?

A bouncing ball or a pendulum eventually stops,
what happens to the energy?

Is it possible to build a machine to perform useful
work without consuming energy? (Such a device is
called a perpetual machine; it creates energy).
A ball hitting a surface both of perfect elasticity
Galilei Galileo (1564-1642) discovered that a body
acquiring a velocity in its descent can rise exactly will bounce back as high as its original height.
as high as it fell, in his study of falling objects in a
uniform accelerating field. He discovered the law of conservation of energy in the conversion
between potential and kinetic energies. Bouncing balls and pendulums illustrate this law. A ball
falling from a height ho looses its potential energy at the same rate as it gains kinetic energy. At
any height hi and a velocity of vi, the total energy is still m g ho,
m g ho = m g hi + (1/2) m vi2
23
When the ball hits the surface, the height becomes zero and it attains the maximum velocity vo,
and m g ho = (1/2) m vo2. This kinetic energy causes the ball to deform, converting to
mechanical energy, which when returned is a force giving the ball an initial velocity - vo. Since
the ball and surface are not perfectly elastic, there is always a loss in height on the return
bounce. The difference in height is a measure of imperfect elasticity of the ball and surface.
Torricelli is well known for the discovery of the barometer. He also studied the flow of
liquid. He observed that a liquid flowing out of the basal orifice of a vessel cannot, by
virtue of its velocity at the efflux, ascend to a greater height than its level in the vessel.
This statement is consistent with the law of conservation of energy.
Other historical observations consistent with the law of conservation of energy came from the
usage and equilibria of pulleys, levers, and other simple machines.
Regarding the conversion between heat and work, the great contributor to the heat engine,
N.L. Sadi Carnot (1796-1832) gave the following theorem: Whenever work is performed by
means of heat, a certain quantity of heat passes from a warmer to a colder body. Carnot
considered the quantity of heat invariable. Clausius took it a step further and considered the
work performed comes from the heat lost.
Time and again, people misinterpreted their observations and claimed they found phenomena
that appeared to have contradicted the law of conservation of energy. So far, no experimental
result has violated this law.
The three laws of motion of Newtonian physics are consistent with the law of conservation of
energy. The body with mass m is a system, and when no energy is given to it, its velocity does
not change (law of inertia). Energy of m can be transferred by a force (law of acceleration).
When two systems do work to each other, equal amount of work are done to each other (law
of action and reaction).
Review Questions:
1. Kathy weighs 50 kg. Calculate the potential energy she gained by climbing to a platform 10 m above a
swimming pool. If she has a free fall, how long would it take for her to reach the surface of the swimming
pool? What is the speed on entry to water? Calculate the kinetic energy when she reaches water. (time =
9.8 s, v = 14 m/s). Let us assume that Kathy comes down very ‘slowly’ from the 10-m platform and
wastes no energy for anything else except to raise her body temperature. Assume the heat capacity of her
body as 0.8 kcal / kg-K (compared to 1.0 kcal / kg-K for water). Calculate the temperature increase of
her body. (Temperature increase = 1.64 kcal / (70 x 0.8 kcal/K) = 0.029 K).
2. The Niagara Falls have a height of 58 m (190 ft). If all the potential energy is converted into heating the
water, its temperature increases. Calculate its temperature increase. (Ans: 0.14o C).
3. Why does sound propagate through a tube with much less attenuation than through open air?

Inspired by Galileo’s writings, Evangelista Torricelli (1608-1647) wrote a treatise on mechanics (De Motu, “Concerning
Movement”), which impressed Galileo. As a result, he was invited to Florence, serving as secretary and assistant during the
last three months of Galileo’s life.
24
4. Why does a beam of light transmit via an optical fiber to a long distance with little attenuation, but a light
beam transmitted through a large body of transparent medium loses intensity?
5. Design an experiment or a demonstration to show one of the following: conservation of energy, conservation
of matter, conservation of electric charge, conservation of momentum, or conservation of matter and energy
regarding them to be equivalent.
Transmission of Energy by Sound Wave
Humans produced the loudest sound by a
nuclear explosion, which sent shock waves
(loud sound) to a great distance.

What is sound?
How do sound waves transmit energy?
Sound waves transmit mechanical energy by
means of pressure and volume change. When
a fluid is disturbed at a point, energy expands
in all directions, showing the disturbance at
distant points by wave propagation. The
average rate of energy transferred per unit
time per unit area of the wave front is called
the sound intensity I, (watt/m2).
Cross-section of sound wave propagation. Dark and gray
circles indicate fronts of certain pressure differences.
As waves, sound is characterized by
frequency, f (Hz), and intensity, I, (watt/m2).
There is no limit in frequency of sound, but human ears detect those in the range of 20 to
20,000 Hz, nearly 11 octaves. Our ears sense pressure variation of 1/10,000,000,000 atmosphere
pressure (atm), and become painful at a variation of 1/10,000 atm. In terms of pressure variation,
the painful threshold is 106 times greater than that of hearing. The intensity, I, is proportional
to the square of pressure fluctuation. Both hearing and painful thresholds depend on the
frequency.
The sound intensity level (SIL) is measured in a decibel (dB) scale, which is based on the
intensity I. At any frequency, the intensity Io just audible is referred to as SILo, and SIL is
SIL (dB) = SILo + 10 log (I/Io).
At 1000 Hz, the threshold (I = 10-12 Watt/m2) of hearing is the reference (SILo = 0 dB). The
intensity causing pain in ears is 1 Watt/m2, corresponding to an SIL of 120 dB,
SIL = SILo + 10 log (1/10-12)
= 120 dB
Comfortable hearing is between 50 and 70 dB, whereas 10 dB is a bel (after A. G. Bell, 18471922). A shock wave is due to a sharp difference in pressure from explosions, including
25
nuclear explosion. Shock waves cause serious injuries to ears, and destroy buildings and
structures.
Review Questions:
1. How do sound waves transmit mechanical energy?
2. Describe the following terms: sound intensity (bell),
and sound intensity level (SIL) (dB).
3. Why does sound propagate through a tube with much
less attenuation than through open air?
4. You stand at a point of 100 m from a blast and
experienced just a painful level (120 dB) of sound.
What are the intensity levels for persons standing at
50 and 200 m from the source? (126 and 114 dB)
Some Energy Units
J, erg
eV, keV, MeV, GeV
cal, kcal, BTU
cm-1 (wave number) s-1 (Hz)
L atm
amu (atomic mass unit)
Conversion Factors of Energy
A certain amount of energy in one form always converts to a definite amount in another form.
One calorie is always equivalent to 4.184 Joules, a value determined by experiment.

What units are used for energy?
Where can you find energy conversion factors?
The SI unit for energy is J (J = N m = kg m2 s-2 = C V), and
other units are given in the text box on this page. Conversion
factors are given in another text box, and on page v.
The unit electron volt (eV) is the energy gained by
accelerating an electron by 1 volt. An electron has a charge of
1.602 x 10-19 C, and 1 eV = 1.602 x 10-19 J. For high energy
particles, units keV (1000 eV), MeV (1,000,000 eV) and Gev
(giga or 109 eV) are used.
Some Conversion Factors
1 MeV = 1.602 x 10-13 J
1 eV/molecule = 23045 cal/mol
1 amu = 1.492416 x 10-10 J
= 931.4812 MeV
1 cal = 4.184 J
1 atm L = 101.3 J
1 eV = 1.602 x 10-19 J
1 J = 1 coulomb-volt
1 joule = 107 ergs
1 BTU = 252 cal
Energy expressed in unit eV is the energy per particle or event. In bulk material, we deal with
quantity in moles. A mole has an Avogardro number of particles. The conversion of units are
illustrated below:
1 eV = (1.602x10-19 J/particle) (6.022x1023 particle /mol)
= 96485 J/mol
= 965 kJ/mol) (1 cal/4.184 J)
= 403 kcal/mol
Review Questions:
1. A BTU is the heat required to heat 1 pound of air free water from 60 to 61 F. Convert 1 BTU to the
equivalent of heat in kJ and kcal from this description. (1 BTU = 252 cal = 1054 J)
26
2. Ten mole of water has absorbed 4184 J (1000 cal) of energy. Calculate the average increase in kinetic
energy of a molecule in eV.
Thermodynamics
The science of how heat behaves is called thermodynamics which was derived from the
Greek words therme (heat) and dynamis (force). It was intensely studied in the 19th century
motivated by the need to convert heat into mechanical work. The fundamental laws of
thermodynamics are useful guidelines for solving many energy-related problems.

What is heat and temperature?
Why energy flow from one place to another?
What are the four laws of thermodynamics?

How can heat be converted into mechanical work? Demonstrate please.

Can all the heat be converted into mechanical work? How much is lost if not all? What
happened to the lost energy?
When the temperature of two bodies are the same, there is no net heat transferred
between them when they are in contact. This is the 0th law of thermodynamics, and we
have applied this law to measure the temperature of an object.
The 1st law of thermodynamics is the law of conservation of energy. An early statement for the
law was given by Clausius: When work is produced by a system using heat, a
proportional quantity of heat is consumed; when work is done to a system, an
equivalent amount of heat is produced.
To facilitate discussion, let us represent a system by A. The heat and work done to A
empowers A to perform work according to its design. The work may be visible as it involves
the expansion or contraction of the volume of A. The work done by A will not be necessarily
equal to the total energy input to A. Some energy is absorbed by A to raise its internal
potential, Eip. Thus, Eip, of the system (A) is equal to the energy q input to the system subtract
the work w done by the system:
Eip = q - w
The internal energy is due to the rise in temperature of A or phase transition for the substance
in A. For example, the melting of ice at 273 K to water at the same temperature is a phase
transition, so is the evaporation of water into vapor. Much work is done in the phase
transition. The first law made it possible to account for all the energy transferred into and out
of a system. Heat spent in raising the internal energy, unrecognized as energy in untrained eyes,
was wastage in engineering processes. The 1st law of thermodynamics is another statement of
the conservation of energy.
There are many implications due to the first law of thermodynamics, and thus it can be stated
differently depending on your purpose. Common dreams are to build machines to perform
27
work without putting energy into it. The 1st law suggests that perpetual motion machines are
impossible.
The 2nd law of thermodynamics summarizes the experiences of converting heat into
mechanical work: It is not possible to build a machine to convert all the heat into work.
In other words, converting heat from one form into another cannot be made without waste,
due to raising the temperature of the surroundings of the system. Most heat conversion
processes are of low efficiency. Thus, the second law is not a limitation of the development of
technology, rather it sets the condition for efficient machines. For example, hot exhaust gas
carries energy with it in an internal combustion engine. The second law suggested that
lowering the temperature of the exhaust extracts more energy of the burning fuel to do
mechanical work.
There are many ways to state 1st and 2nd laws of thermodynamics, depending on the purpose.
Those given here are intended to give a general description of how heat behalf.
A closed system is an isolated one such that no energy or mass is transferred into or out of. A
closed system can be either at equilibrium, a state with no detectable change, or noneequilibrium, changes may still take place. For example, two liquids at the same temperature in
a container will eventually mix. In this case, the driving force (energy) of change is called
entropy, which is related to randomness for a collection of molecules or objects. Increasing of
randomness and flowing of heat causes entropy to increase. For a perfect crystal at absolute
zero (0 K), there is no available heat, and the entropy of any perfect crystal at 0 K is defined as zero.
When a crystal or system absorbs heat, its entropy increases. When heat flows from one part to
another part in a closed system, the entropy of the closed system increases. In a closed
system, the 3rd law of thermodynamics states that the entropy tends to increase.
The laws of thermodynamics can be summarized in a sentence. Energy of a closed system
strives for the lowest state, but its entropy strives for the highest state.
Review Questions:
1. What are the four laws of thermodynamics?
2. What is the implication of the 0th law of thermodynamics?
3. Design an experiment or demonstration to show that energy is conserved.
4. What is entropy?
28
Technology for Energy Conversion
The better the technology for utilization and production
of energy we have, the better is our living standard.
Thus, scientists, engineers, architects, politicians, and
almost everyone are concerned with these issues:
At the end of the 17th century, energy
resources from the Earth surface had
exhausted, and deep coal and metal ore pits
suffered from floods by underground water.
Steam engines in 1763 converted 2% of heat
into useful work, but it filled the need at the
time. Following the use of steam came the
internal combustion engine, and the industrial
revolution, which caused many social
problems. Thus, directing energy movement is
more than a technical problem, it involves
social, economic and human factors.

How to make efficient use of energy? How to
control the movement of energy?

How to develop technology making the most
efficient use of energy resources?

What will be the energy demand in the near future?
How to structure a community suitable for the available energy?
Machines are needed to recover residual heat; work is required to transfer heat from a cold
place to a hot place (air conditioning). The laws of thermodynamics mentioned above must be
considered in the utilization of heat. For the transfer of electric energy, laws of electricity and
magnetism must be considered. Energy loss through transmission lines is often cited for the
research on superconductor (or perfect conducting) materials.
For the transmission of radiation, the wavelength of radiation dictates the transmission
medium. Infrared lens, microwave guide, fiber optics, ultraviolet filter, X-ray and gamma ray
shielding are some of the gadgets related to the technology of radiation transmission.
Batteries, motors, photoelectric cells, internal-combustion engines, thermoelectric generators,
electrochemical cells, fuel cells, etc. are machines for energy conversion. They convert energy
from one form to another.
Part of nuclear technology is to build machines for the conversion of nuclear energy into heat
and electric energy. The development of nuclear technology is closely related to the
development of other technologies.
Review Questions:
1. What energy resources are available on the surface of the Earth? What is the origin for each of the
resources? Give an energy cycle involving some of energy resources.
2. Why are incandescent light bulbs much less efficient in converting electric power to light than fluorescence
bulbs?
3. Why a microwave oven takes shorter a period to warm up the same amount of water than the stove even if
they operate at the same power?
29
Energy Resources and their Utilization
Solar, nuclear, and geothermal energies are the ultimate sources of our energy, with the solar
energy being most important for the Earth. The Sun is a nuclear fusion reactor, and nuclear
technology is being developed to imitate the energy producing process of the Sun.
Solar Energy
The Sun provides nearly all energy on Earth. It provides wind power, hydropower, tides,
waves, and plants, causing nearly all the global phenomena, floods, draught, tornadoes,
hurricanes, plant growth, life, death and decay. Fossil fuel is energy from the sun long ago.

How much solar energy reach the Earth
surface, and in what form?
What process provides the solar energy?
What is the total energy output of the Sun?

What phenomena are caused by solar energy?
What energy resources on Earth do not
come from the Sun?
Energy from the Sun is in the form of infrared
(heat), visible, and ultraviolet radiation.
The Sun’s surface radiates 6.4 kJ cm–2 s–1, and the surface of the Sun is 6.1x1012 km2, (1 km2 =
1010 cm2).
On a cloudless summer day, the earth surface receives 80 kJ cm-2 day–1 (20 kcal cm-2 day–1).
These values are important for any solar technology. The Earth receives 1.7x1014 kJ s–1 of
energy from the Sun.
As to what provides the energy in the Sun, a detailed answer requires a lengthy discussion, and
this will be discussed in the chapter on nuclear fusion. To make a small Sun on earth is one of
the objectives of nuclear technology.
Review Questions:
1. What is the total power output of the Sun? Where does the energy go? What fraction of the energy from the
Sun reaches the Earth?
2. The distance between the Sun and the Earth is 149,600,000 km. What is the time of flight for a photon
from the Sun to the Earth? (8.3 m)
30
Geothermal and Nuclear Energies
Cross Section of the Earth
Geothermal energy is heat in the interior of the Earth, and
nuclear energy is derived from materials present on Earth
accessible to man.

What are the sources of energy?
Which is a major and which is a minor source of energy?
Earth
crust
Lower
mantle
Geothermal energy refers to the heat flow of the planet
Inner
Earth. In this regards, thermal gradients, conductance of
core
various material, thermal history, and heat distribution of
Outer
Upper
Earth are information required for the development of
core
mantle
technology to utilize this heat source. Aside from the heat in
the hot interior of the earth, radioactive decay and other
nuclear process may produce a small amount of heat in the interior of the planet Earth.
The heat flow from the interior to the surface of the Earth is small, only 0.063 J m–2. The
temperature at depths less than 20 m oscillate annually, but it remains constant at greater
depths. The earth crust is a poor thermal conductor. Little amounts of energy are derived from
geothermal sources using machines such as heat pumps, in some limited areas where there are
hot springs.
Another source of energy not coming from the Sun is nuclear power, which can be divided in
two categories: fission or splitting of heavy elements such as uranium and plutonium, and
fusion or combination of light elements such as hydrogen, tritium, and deuterium. The science
of these processes is very simple, but the technology for their utilization and maintenance is
very complicated. Many aspects should be studied. The major purpose of this book is to
introduce the various aspects related to nuclear phenomena, and the minor purpose is to
consider the impact of nuclear technology on various issues.
Radioactive decays also produce energy, but the amount of energy is small for any large-scale
application as a source of energy.
Review Questions:
1. What are the major energy resources on the planet Earth?
2. What is a heat pump? How does a heat pump get an efficiency of 200%? Is the principle of conservation of
energy violated in this case?
31
Energy Conservation
Energy conservation means preservation
of energy supplying commodities or
making the most efficient use of energy.
The media coined this phrase between
1974-1978, a period when the energy crisis
hit every country.
The Energy Crisis
On October 17th, 1973, the leaders of Arab nations met in the
Capital of Kuwait to proclaim an oil boycott (Darmstadter,
1975). Between 1974 and 1978 the Organization of
Petroleum Exporting Countries met regularly and set the oil
prices. This triggered the energy crisis during 1974 - 1978.
During the period of energy crisis, gasoline price was high,
and many gas stations limit the purchase of gasoline to 10
gallons each time. Many gas stations did not have enough
supply, and motorists often had difficulty buying gasoline.
Since energy is always conserved, the
terms conserving energy and energy conservation
are fallacious, non-scientific, and
Due to the high cost of transportation, prices of goods and
erroneous. However, these terms had
services went up, causing a high inflation rate. Inflation cut
been used since the seventies to mean
the purchase power of workers, and wage demand of labor
making more efficient use of energy, extend the
went up. Thus, the energy crisis caused social problems.
limit of energy utilization, and not to waste energy.
Their usage is so common that we can no
longer ignore it. The energy crisis prompted the concern over the environment in the 1980s
and 1990s. The realization of a limit in chemical energy reserve on the planet Earth led to the
recognition of the Earth being a limited ecological system.

In your opinion, will energy demand of the world cause a crisis in the future?

How can you extend the benefit of energy utilization as an individual, as a group, as a
nation or in the global village?

What will be used to supply energy for the world when oil and coal are depleted?
Having experienced the energy crisis made all oil-dependent nations, especially the U.S.,
nervous when Iraq invaded Kuwait. Oil or energy was certainly an important factor for the
Persian Gulf War in 1991.
Review Questions:
1. List ten tips for saving energy in your home.
2. List ten rules for a university to save energy.
3. Discuss the impact of doubling the price of gasoline.
4. How is urban design related to energy consumption of a
community?
32
Lessons Learned from Energy Crisis
In the long run, the energy crisis was a good lesson for
the world to learn that energy reserve is limited. The
public has been warned for some time, but no one
listened until the crude oil price reached $40 a barrel.
The hardship during this period pushed the
developments of technology for better utilization of
energy. Cars making more efficient use of energy were
built, methods were developed to derive more fuel from
lower grade crude oil, alternate fuels were tried, and
other energy sources than oil were tapped.
The Impact of Eenergy in
Society
Level
Demand
Energy consumption is a measure of living standard.
As the living standard improves world wide, energy
consumption and demand increase.
Cost

How do you manage your personal energy
consumption to derive the most benefit?

How does a society manage the energy supply,
demands, and utilization?
What forces are used to manage energy?
Arbitrary Coordinate
Typical curves depicting market forces of price and
demand.
There are two forces to control energy demands: cost and regulations. Cost is related to price
of energy and income, Cost is the market force that is less noticeable than government
regulations. Regulations are often seen as heavy-handed. In Canada and the United States, the
market force dominates, but occasionally the government steps in with regulations. Taxing
policy, however, has a hand on each of the two forces.
Cost is determined by taxes, level of supply, differential pricing due to amount of consumption
and purpose of end use etc. When the cost is high, the demand is low, and as cost is lowered,
the demand goes up. Because the cost and demands vary as curves, the market force is more
acceptable for the public. How the market forces work is a subject discussed in an introductory
economic course.
Regulation by policy sometimes is brought about suddenly, and this force may not be popular.
However, in the formulation of a policy, there are many factors to be considered. Energy
demands is a function of population, population density, work force, number and type of
industries, income level, social acceptance etc. Sound policies work, but unfit policies invite
abuse and protests.
Regarding nuclear energy, its development is expensive at the initial stage with only a slim
prospect of return on investment. Initially, only government allocates funds for the research
and development. The cost of development may not be added to the pricing in the sale of
nuclear power.
Review Questions:
1. What are the major forces for the management of energy related commodities and technologies in the public
domain?
2. Discuss how costs affect your personal consumption of energy?
33
Exercises
1. Write an essay using one of the following as your title: Hotness and heat; Mechanical work
and heat; Energy as driving force of change; Conservation of energy and energy
conservation; Black out (power failure); The visible light; Electromagnetic radiation;
Infrared; X-rays; Photoelectric effect; Methods of energy storage; Conversion of energy;
Energy mass equivalence; Entropy; Sound and music; Fighting for energy (energy related
wars); Conflicts over energy; Energy policy of a household; Guidelines of energy usage
for an institution; The sun.
2. From a reliable source, find information about and then write a short story on any one of
the following people. Make your story interesting to read. Plato (427-347 BC); Newton, I
(1643-1727); Fahrenheit, G.D. (1686-1736); Celsius, A. (1701-1744); Charles, J.A.
(2746-1823); Gay-Lussac, L. (1778-1850); Seebeck T.J. (1770-1831); Black J. (1728-1799);
Thompson B. (1753-1814); Joule (J.P. (1818-1889); Young T. (1773-1829); Bernoulli D.
(1700-1782); Clausius R.J.E. (1822-1906); Maxwell J.C. (1831-1879); Thomson W.;
Boltzmann L.E. (1844-1906); Watt J. (1736-1819); Galileo (1564-1642); Torricelli E.
(1608-1647); Carnot N.L.S. (1796-1832); Planck M.K.E.L. (1858-1947); Strutt J.W.
(1842-1919); Wien W. (1864-1928); Einstein A. (1879-1955).
3. A 12 fl-oz serving (350 mL or 260 g) of beer contains 7% (by volume) alcohol is rated to
give a food energy of 150 kcal. As an approximation, assume all the energy comes from the
alcohol. Calculate the food energy value of 3.5 fl oz table wine containing 12% (by volume)
of alcohol. Ignore the small amount of other chemicals present in wine and beer. Express
this amount of energy in kJ, and kilo-watt-hour. Assume you use the energy to raise your
potential energy by going vertically up a height. What is the height? If you have this
amount as kinetic energy, what is the velocity?
4. Calculate the velocities of a neutrons which have a kinetic energy of 0.52 MeV and 0.025
MeV. (Ans: 1.0 x 107 m/s and 997 m/s respectively without using the theory of relativity,
which should be used for the high-energy neutrons). What is the velocity of an electron if
it has a kinetic energy of 0.52 and 0.025 MeV? Should you use the theory of relativity to
calculate the kinetic energy of electron?
5. Energy content of 36 g liquid water at 273 K is 12 kJ more than 36 g ice at the same
temperature. Calculate the mass equivalence of 12 kJ in g and in amu. Is this amount
detectable with a balance that can be used to weigh 36 g? Do the same for 1200 kJ and
1x1012 kJ.
6. Do you expect the temperature of water to be different before and after it flow down a
waterfall of say 500 m? What happens if all the potential energy is converted to the kinetic
energy of the water molecules?
7. What are the three laws of Newtonian physics? What are the four laws of
thermodynamics?
34
8. Which one do you favor as an instrument to manage energy resources, free market force
or government regulations?
9. Give the energies of the photons in units eV
and Hz for various regions of the
electromagnetic radiation spectrum.
Photon Energy in Various Region of the
Electromagnetic Radiation Spectrum
Region,
Radio (long)
Radio
Radio (short)
Infrared
VISIBLE
Ultraviolet
X-rays
Gamma rays
35
in eV
in Hz
Further reading and work cited
Brandwein, P.F., Stollberg, R, Burnett, R.W., (1968), Energy, its forms and changes, Harcourt,
Brace & World, Inc.
Darmstadter, J. (1975), Conserving energy, John Hopkins University Press.
Einstein, A. (1905), On the electrodynamics of moving bodies (Zur Elektrodynamik bewegter Körper),
original in Annalen der Physik 17, 891, reproduced in The collected papers of Alber Einstein, vol. 2,
276, Edited by Stachel, J, Prenceton University Press (1989).
Einstein, A. (1909), On the development of our views concerning the nature and constitution
of radiation (Über die Entwickelung unserer Anschauungen über das Wesen und die Konstitution der
Strahlung) reproduced in ibid, vol. 2, 564.
Maiman, T.H. (1960), Stimulated optical radiation in ruby, in Nature, 187, 493.
Weber, M.J. (1982), CRC Handbook of laser science and technology, vol I, Lasers and Masers, CRC
Press.
Zukav, G. (1979), The dancing wu li masters, Bantam Books.
Web Sites on Energy
Energy outlook and policy:
http://www.igc.apc.org/awea/wew/othersources/otheroutlook.html
Energy and economics:
http://www.investaweather.com/energy/energyhmpg.htm
Energy and environment research center:
http://www.eerc.und.nodak.edu/
36