Research topics in physics pptx

Physics

Physics has an important role in our life. Without physics and the work of
physicists, our modern life would not exist. Using physics, people created machines,
instruments and some different divices from the crudest to the most modern aspect.
Techology is developed more rapidly, more modern day by day.
Moreover, all other natural sciences- example chemistry, biology, medicine-
depend upon physics for the foundations of their knowledge. Physics holds this key
position because it is concerned with the most fundamental aspect of matter and
energy and how they interact to make the physical universe.
Physics has some main problems: mechanics, electricity and magnitism, heat,
wave and sound, optics, nuclear physics, atomic particles.

CHAPTER 1: MECHANICS

Mechanics is a branch of physics concerned with the behavior of physical
bodies under the effect of the bodies on their enviroment. The early modern period,
scientists, such as Galileo, Kepler and especially Issac Newton, laid the foundation
for a field of mechanics and now it is known as classical mechanics or Newtonian
mechanics.
Mechanics has two major divisions: classical and quantum mechanics.
Classical mechanics came first while quantum mechanics did not appear until 1900.
Both commonly constitute the most certain knowledge that exists about physical
nature.
Classical mechanics is concerned with the physical laws governing the motions
of bodies. It is used for describing the motion of marcroscopic objects, such as: parts
of machinery, astronomical objects inclue spacecraft, planets, stars, galaxies. It is one
of the oldest and lagest subjects in science, engineering and technology.
Classical mechanics is divided into: statics, dynamics and kinematics. Statics
studies matter at rest or in motion with constant velocity. It deals with the balancing
of forces with approriate resistance to keep matter at rest. It is commonly used for

designing buildings and bridges. Different from statics, dynamics studies matter in
motion, example motion of stars, baseballs, gyroscopes of the water pumped, and
even air plane. Kinematics studies motion without regard to the forces present. It is
simply a mathematical way to describe motion.

Three Newton’s laws:
Classical mechanics is governed by three basic principles, which were first
formulated in the 17
th
and 18
th
centuries by Isaac Newton. These principles are
known as Newton’s laws.
The first law describes a fudamental property of matter, and often called the
“Law of Inertia”, as follows: Every object in a state of uniform motion tends to
remain in that state of motion unless an external force is applied to it. The key point
here is that if there is no net force acting on an object (if all the external forces cancel
each other out), the object will maintain a constant velocity, if that velocity is zero,
the object remains at rest and if having an external force to apply, the velocity will
change.
Newton’s second law describes the manner in which a force compel a change
of motion, at a rate of change called acceleration. It can be state as follows:
F=ma
Where
F: the applied force
m:mass of the object
a: the object’s accerleration

Acceleration and force are vectors, in this law the direction of the force vector
is the same as the direction of the acceleration vector.

This law allows quantitative canculations: how do velocity change when forces
are applied. Notice the fundamental difference between Newton’s 2
nd
law and the
dynamics of Aristotle: according to Aristotle there is only velocity if there is a force,
but according to Newton an object with certain velocity maintains that velocity unless
the force acts on it to cause an acceleration.
Newton’s third law can be stated as follows: For every action in nature there is
an equal and opposite reaction. In other words: if object A exerts a force on object B,
then object B also exerts an equal force on object A. Notice that the forces are exerted
on different objects.
This law explains what happens if we step off a boat onto the bank of a lake: as
we move in a direction, the boat tends to move in the opposite direction.

Mass, force and acceleration
Mass is the amount of matter in a body. The mass of a body remains constant.
In the metric system mass is measured in kilogram (kg). Sometimes we use weight,
or the pull of gravity upon matter. The object’s weight depends on the gravitational
pull acting on it. An object’s weight is much less on the moon than it is on the Earth,
and in outer space a body’s weight may be nearly zero.
When an object’s velocity changes, it accelerates. Acceleration shows the
change in velocity of a body in a unit time. According to Newton’s 2
nd
law, it is direct
result of the applied force. In the metric system, acceleration’s unit is (m/s)/s.
When we study mechanics, we can know a concept: force. Force is a vector
quantity that has both a specific magnitude ( size or length) and direction. It is
characteristic for a body’s acting to other. It changes the motion of a free body or
cause stress in a fixed body. It can also be described by concepts such as a push or
pull that can cause an object with mass to change its velocity, to accelerate, to

deform.
If two forces applied simultaneously to the same point have the same effect as
a single equivalent force, called resultant force. We can canculate the net force:
F=F1+F2+… .
If two forces acting on an object is the same direction (parallel vectors), the
resultant force is equal to F1+F2, in the direction that both two forces. If two forces
acting on a object is opposite directions, the net force is equal to |F1-F2 |, and
direction of whichever one has greater magnitude. If the angle between the forces is
anythingelse, the net force must be added up using the parallelogram rule.
The same forces can have different effects depending on applied way and
applied body. A force may cause a body to spin or rotate if applying in a certain way.
The tedency of a force to rotate the body is known as torque, it is also a vector
quantity. Its magnitude can be calculated by multiplying applied force to the distance
between the line of force and the axis of rotation.
A kind of force which resists the motion of a body along a path is friction. It
appears only when other forces are applied or if a body is already in motion. It may
be undersirable in some cases, example: air resistance that slows down an airplane,
but in some other cases, it is useful, example: car brakes.

Center of gravity and equilibrium :
It’s difficult to apply the laws of mechanics to a particular body. The problem
is more simple if we study the behavior of an object’s center of gravity instead of
studying the behavior of entire pbject. The center of gravity is a point at which the
weight of a solid object can be considered to be concentrated . all forces appear to act
upon this center. If the line of exerted force does not pass through the center of
gravity, a torque is created.
A body can be completely at rest if all forces and all torques are balanced. A
complete balance exists. If the sum of all forces and torques acting on a body is equal
zero, we say that the body is in equilibrium.
A body in equilibrium may be in one of three states: stable, unstable, neutral

equilibrium. When a torque apply to a body, after the torque ceases to act, if the body
tends to return to its original position, it is in stable equilibrium. If it continues to turn
to a new position, it is known as unstable equilibrium. The body is in neutral
equilibrium if it comes to rest wherever it may be when the torque is removed.

Work, energy and power
Work: when a force makes a body move, the product of the force times the
distance through which the force acts is called the work done by the force. There are
some example of work which we can observe in everyday life: a horse pulling a plow
through the field, a man pushing a cart, a weightlifter lifting e barbell above his head,
etc. Mathematically, work can be canculated by the following formula:
A=F d cosα
Where
F: the force ( in Newton)
d: the distance through which the force acts (the displacement), (in meters)
α : the angle between the force and the displacement vector.
Energy is the capacity for doing work. If work is done on a body, the energy of
the body increases. Energy is consists of kinetic and potential energy. Energy
associated with motion is kinetic energy. It is equal to one half the product of its mass
times the squre of its velocity represented by a formula:
KE = (1/2)mv
2

Where:
KE: kinetics energy (in Joule)
m: mass ( in kg)
v: velocity (in m/s)
Potential energy exists whenever an object which has mass has a position
within a force field. The most everyday example of this is the position of objects in
the earth’s gravitational field. In this case, the potential energy of an object is given

by:
PE = mgh
Where: PE: potential energy ( in Joules)
m: mass ( in kg)
g: gravitational acceleration of the earth ( 9.8 m/s/s)
h: height above earth’s surface ( in m)

Conservation of energy
This principle asserts that in a closed system energy is conserved. This
principle will be tested by the experiment in the case of an object in free fall. When
the object is at rest at height h, all of its energy is PE. As the object falls and
accelerates due to the earth’s gravity, PE is converted into KE. When the object
strikes the ground, h=0, so that PE=0, the all of the energy has to be in the form of
KE and the object reaches the maximum velocity. In this case we are ignoring air
resistance.
Power is the rate of doing work or the rate of using energy. Unit of power is
watt. If we do 100 joules of work in one second ( using 100 joules of energy), the
power is 100 watts.

Some simple machines.
Many principles of mechanics are clearly demonstrted in devides called simple
machines. These machines have been known since antiquity with crude machines or
now with modern machines. They are the lever, the wheel and axle, the inclined
plane, the screw, the rope-and-pulley system. They are designed to amplify the effect
of forces or to do work to move weight or to overcome resistances.

Chapter 2: Heat

Definition and applications
All living things need heat. Heat is a form of energy transferred from one

object to another caused by a different in temperature between these objects. Some
other words:
- Heat is defined as energy in transit from a high-temperature object to a lower
one.
- Heat is a form of energy possessed by a substance by virtue of the vibrational
movement of its molecules or atoms.
- Heat is the transfer of energy between substance of different temperatures.
Heat has an important role in our life. It causes natural changes which occur in
an endless cycle. To explain some phenomena in the nature, we can use concept of
heat. Example the atmosphere in tropical areas is hotter than it in polar areas because
tropical areas receive more heat from sun.
The amount of heat from the sun that falls on the region determines the
temperature range of the region. The temperature of environment effect to plant,
animal and even man. Heat is a very important factor in making our life and our
world.

The nature of heat.
Despite having many definitions of heat, heat has one nature. We can know
heat when we were a child. We could detect it easily through its effect: burning. But
do you know what heat itself actually is? Heat cannot be weighed and cannot be seen
or heard too.
To understand the nature of heat, we may study its acting, we can use the
kinetic theory of matter. According to this theory, all matter made of atoms and
molecules in constant motion. When matter absorbs energy, the random internal
energy and the motion of these atoms and molecules are increased. This increase
makes itself in the form of heat, and when it occurs, the temperature of the matter
rises. This leads a conclusion: when the energy of motion has been transferred to the
random motion of the atoms that make up the matter, the motion of the atoms is
speeded up and heat is produced. That is the nature of heat.

Sources of heat
Heat is very necessary for life, so it is important to know where it comes from
and how it can be used. The most important source of heat for our Earth is the
radiation from the sun. The Earth absorbs a part of heat from the sun. This keeps the
temperature of the Earth’s surface and atmosphere at a level which permits life to
continue.
The second important source of heat is the store of natural fuel on and in the
Earth, such as: coal, oil, gas, wood. They do not provide heat constantly and
automatically as the sun does. They are composed of carbon, hydrogen, and other
elements. In a certain temperature, the combustion occurs, the fuels react chemically
with oxygen. This reaction releases a large quantity of heat.

The definition of specific heat.
The specific heat is the amount of energy that is transferred to or from one unit
of mass or mole pf a substance to change its temperature by one degree. Specific heat
is a property, it depends on the substance under consideration and its state.

The temperature
Temperature is the property that gives physical meaning to the concept of heat.
And object has low temperature if it is cold, and vise versa. When contacting with a
cold body, a hot body gives up some of its heat to the cold one. The process will
continue until both have the same temperature.
Definition of temperature is based on some constant value, absolute zero.
Absolute zero is defined as the temperature at which all molecules and atoms’ motion
stops completely. It is equal to -273.16 Celsius or 0 Kelvin. We can define
temperature as: temperature of a substance is a measure of the intensity of motion of
all atoms and molecules in that substance.
To measure temperature, we use the themometer scale. Its working is based on
the fixed points of boiling water and freezing water. There are four scales:
Fahrenheit, Celsius, Kelvin, Rankine. We can change from this scales to different

one. Some useful conversation relation:
Fahrenheit to Celsius: T(C)=5/9(T(F)-32)
Celsius to Fahrenheit: T(F)=9/5 (T(C)+32)
Celsius to Kelvin: T(K)=T(C) + 273
Fahrenheit to Rankine: T(R)=T(F)+460

Kinetic Theory
Heat is not a material fluid. It is the result of a conversion of energy. It is a
form of energy. It is equivalent to mechanical energy. We have a conversation: one
calorie of heat energy is equal 4.184 joules of mechanical energy. In an isolated
system, work can be converted into heat at ratio of one to one.
Three laws of thermodynamics:
The zeroth law: Energy can be only transferred by heat between objects (or
areas within an object) with different temperature.
The first law: in an insolated system, work can be converted into heat at ratio
of one to one.
The second law: Heat transfer happens spontaneously only in the direction
from the hotter body to the colder one.

The Transfer Of Heat
Heat transfer helps to shape our world. Heat always travels or flows from a
high temperature to a low temperature. In the nature, there are three different methods
of transfer heat. They are: radiation, conduction, and convection.
Radiation
Radiation is a process of transferring heat energy from one place to another.
This process occurs when the internal energy of a system is converted into radiant
energy at a source such as heater. This energy is transmitted by invisible wave
through space. Example the sun radiate heat outwards through the solar system.
Finally the radiant energy touch a body where it is absorbed and converted to internal
energy. And then heat appears. By radiation, heat only travels in space or in gases.

All bodies, whether hot or cold, radiate energy. The hotter a body is, the more
energy it radiates. A body at constant temperature radiate energy continously. It is
receiving energy at the same rate that is radiating energy. So it doesn’t change in
internal energy or temperature.
Radiation transfer depends upon the shape of the radiating object. It is not
proportional to the difference in temperature between two object but it is proportional
to the fourth powers of the absolute temperature.
Conduction
Conduction is the most significant means of heat transfer in a solid. If one part
of a body is heated by direct contact with a source of heat, the next parts become
heated. This may be explained by the kinetic theory of matter. When the temperature
increases, heat motion of molecules raises, this violent motion passes along the body
from this molecule to another and result: the body is heated and this process is known
as conduction. Example, if dipping simultanously a silver and a wood spoon into
boiling water, the handle of the silver one rapidly becomes hot while the wood one
still is cool.
Materials in which heat transfer happens easily and quickly are known as good
conductors, example all metals. In meterials such as wood, rubber and air, heat is not
transferred readily from one molecule to the next, they are called insulators.
Conduction occurs readily in good conductors of heat. Conduction depends upon the
different of temperature and the resistance of the flow of heat. The greater the
temperature difference between two point is, the more the driving force to move heat
is. The less resistance is, the easier heat transfer is.
Convection
The third method of heat transfer is covection. It happens in liquids or gases
(commomly called fluids). Convection occurs when having the change of density
(mass per unit volume). If heating fluid, its density decreases, so it becomes lighter.
The part of warmer fluid will rise while the part of colder will decend. This process
happens continously until having balance in temperature. Some examples in the fact:
water in a kettle is heated by convection; the air in the room is heated by convection

when putting a stove in that room; or when we drop a few crystals of potassium
permanganate into water, we can see movement of pink water, convection occurs.

Chapter 3: Electricity
Electricity is a general term heat emcompasses a variety of phenomena
resulting from the presence and flow of electric charge. These inclue many easily
recognizable phenomena, such as lightning and static electricity.
In general usage, electricity refers to a number of physical effects. However, in
scientific usage, it inclues these related concepts: eletric charge, electric current,
electric field, electric potential difference, electromagnetism.
Electrical phenomena have been studied since antiquity. Until the 17
th
and 18
th

centuries, advances in the science were not made. And until the late 19
th
century,
engineers were able to put it to industrial and residential use. The rapid expansion in
electrical technology at this time transformed industry and society. Electricity almost
has no limits, it can go anywhere, even far into space. It has applications in transport,
heating, lighting, communications and computation. We cannot imagine today’s
world without it. Electricity keeps an important role in our world.

Electric Charge
Electric charge is a property of subatomic particles, it determines those
particles’ electromagnetic interactions. Charge originates in the atom. Atoms cotains
two kinds of charge: negatively charged electrons and positively charged protons. In
an isolated system, charge is a conserved quantity. Within the system, charge may be
transferred between bodies following two ways: direct contact or passing along

conducting material. The informal term static electricity refers to the net presence of
charge on a body, usually caused when rubbing dissimilar together, transferring
charge from one to another.
A light-weight ball suspended from a string can be charged by touching it with
a glass rod that has been charged by rubbing with a cloth. If a similar ball is charged
by the same glass rod, two balls will repel each other. They also repel each other if
they are charged by rubbing with an amber rod, and the other by an amber rod, two
ball attract each other. These phenomena were investigated in the late 18
th
century by
Charles Augustin de Coulomb. He discovered the well-known conclusion: like
charges repel and unlike charges attract each other. He gave a law to show the
relationship between amount of electric force that two charged objects exert upon
each other and the distance separating them, called Coulomb’s law. This law is stated
by the formula:



Where: r: the distance between two charges
k: a constant for converting units of charge and the distance into units of
force
q1,q2: charges of two objects.
The charge on electrons and protons is opposite in sign. The mount of charge is
usually given the symbol q, and its unit is coulombs (C). Each electron carries the
same charge, about -1.6022.10^-19 (COP TREN MANG NHE), and the proton is
+1.6022…
In a atom, if numbers of protons and electrons are equal, the atom is neutral. If
a neutral loses electrons, it has an excess number of protons and it is positively
charged. If a neutral atom gains electrons, it has an excess number of electrons and it
becomes negatively charged.

Electric Current
An electric current is the movement of electric charge. This moving charge
may be electrons, protons, ions, even positive “hole” in semiconductors. We calculate
the current by the formula:

Where
Q: the total charge ( in coulombs)
t: the time (in seconds)
The current I is measured in amperes. A one-ampere current means that one
coulombs of electric charge passes each point in the circuit each second. Addition to
coventional current has been described as the direction of positive charge motion.
Electric Field
The concept of electric field was introduced by Michael Faraday in the 19
th

century. Electric field is space that surrounds a charged object and exerts a force on
any other charges placed within the field. We all know that charged object can exert
forces on uncharged objects over a distance. We use the electric field to describe
possible effects at a point in space about an electric charge. An electric field generally
varies in space, its strength at a point E is defined as:
E=F/q
Where
F: the electric force on a test charge
q: the size of the test charge placed at that point
The electric field strength is a vector quantity, having both magnitude and direction.
Specifically it is a vector field.
The study of electric field created by stationary charges is called electrostatics.
The field may be visualized by a set of imaginary lines. These lines give an overview
of the electric field, their direction at any point is the same as that of the field. These
lines are called “lines of force”. This concept was introduced by Michael Faraday.

The field lines are the parths that a point positive charge would to seek to make as it
was forced to move within the field. They have key properties:
- They originate at positive charges and end at negative charges
- They must enter any good conductor at right angles
- They may never cross nor close in an themselves.

Electric Potential
Placing a positive test charge near a fixed positive point charge, it will
accelerate away and increase in velocity and klinetic energy. But to move this
positive test charge back toward the fixed positive charge, we must do a work on the
test charge. The energy put into this process is stored as electric potential energy. The
electric potential at any point is the energy required to bring a unit test charge from
an infinite distance slowly to that point. It is measureed in volts, one volt is the
potential for which one joule of work must be done to bring a charge of one coulomb
from infinity. In the fact, we don’t often use this concept. A more useful concept is
that of electric porential difference. It is a measure of this change in energy as the
charge moves from one place to another in an electric field. It is given by defining
energy change to charge moved. Its unit is volt. Sometimes it called voltage. When
the voltage is zero ( or electrical potential between points in a field is not different),
electric charge does not move between those points. When potential different
between two points in a field is large, positive electric charge will tend to move from
higher to lower potential and negative charge will move the opposite way.

Electromagnetism
In 1821, the Danish scientist Han Christian Oersted discovered magnetic field
that existed around all sides of a wire carrying an electric current. If bringing a
compass near a current carrying wire, its magnetized needle would realign. If the
current is reversed in direction, the compass needle reverse its orientation. A
magnetic field is created arround the current-carrying wire. We can represent this
magnetic field as a series of concentric field lines in planes perpendicular to the

current, called the magnetic field lines. When the direction of current is known, we
can use the right-hand rule to find the field direction. That rule can be stated as: put
the right hand with the thumb pointing in the direction of current and the finger
encircles the wire, the magnetic field lines are the same direction as the fingers. Or
we can predict the field direction by using a magnet: the direction of the magnetic
field is from north to south pole of magnet.
Magnetism and electricity have a direct relationship. A current exerts a force
on a magnet and a magnetic field exerts a force on a current. Magnetism is induced
by an electric current is known as electromagnetism and the field which it works is
callled electromagnetic field.
Ampere investigated the relationship between electricity and magnetism. And
he discovered that two parallel current carrying wires exerted a force upon each
other: two current in the same direction attract each other, and vise versa, currents in
positive direction repel each other.

Electric Circuit
A basic circuit can be described as: the voltage source, example battery, is
connected with a resistor R through wires, a current I from the source transfer
through the resistor, and from the resistor, the current returns to the source. An
electric circuit is produced. If the source is the a battery, between the terminals of the
battery there is a potential difference, under acting this potential, electrons flow in
one direction, away from the negative terminal toward the positive. The current has a
direct relationship to the voltage of the battery, and it depends on the nature of the
conductor. This relationship is shown in Ohm’s law which was stated in the 19
th

century by Georg Simon Ohm. This law is given by a formula:
U = IR
Where
I : the current ( in amperes)

U : the potential difference (in volts)
R : the resistance (in ohms)

Chapter 3: Optics
Optics is the branch of physics which studies the behavior and properties of
light, including its interactions with matter and the construction of instruments that
use or detect it. Optics usually describes the behavior of visible, ultraviolet, and
infrared light.
Most optical phenomena can be accounted for using the classical
electromagnetic description of light. However complete electromagnetic descriptions
of light are often difficult to apply in practice. Practical optics is usually done using
simplified models. Optics have two fields: geometrical and physical optics.
Geometric optics studies light as a collection of rays that travel in straight lines and
bend when they pass through or reflect from surfaces. Physical optics is a more
comprehensive model of light, which includes wave effects such as diffraction and
interference that cannot be accounted for in geometric optics. Historically, the ray-
based model of light was developed first, followed by the wave model of light.
Progress in electromagnetic theory in the 19th century led to the discovery that light
waves were in fact electromagnetic radiation.
Optical science is relevant to and studied in many related disciplines including
astronomy, various engineering fields, photography, and medicine (particularly
ophthalmology and optometry). Practical applications of optics are found in a variety
of technologies and everyday objects, including mirrors, lenses, telescopes,
microscopes, lasers, and fiber optics.

Geometrical Optics
Geometrical optics describes the geometrical aspects of imaging, including
optical aberretions. It is concerned with the priciples that govern the image-forming
properties of mirrors, lenses, and similar devices. It deals with wht happens when
lighgt strikes different types of surfaces.

Reflection
Reflections can be divided into two types: specular reflection (mirror-like) and
diffuse reflection (retaining the energy). This division depends on the nature of the
interface.
A mirror provides the most common model for specular light reflection. It
consists of a glass sheet with a metallic coating where the reflection actually occurs.
Reflection also occurs at the surface of transparent media, such as water or glass. We
know that a light ray passing through a vacuum or a transparent substance moves in a
straight path. When it strikes the surface of a different substance, part of it is
reflected. The angle at which the ray strikes the surface, called the angle of incidence
θ
i
, and the angle at which it bounces off, called the angle of reflection θ
r
. We always
have θ
i
=θ
r
. If the reflecting surface is very smooth, the reflection of light that occurs
is called specular or regular reflection. The laws of reflection are as follows:
-
The incident ray, the reflected ray and the normal to the reflection surface at
the point of the incidence lie in the same plane.
- The angle of incidence equals the angle of reflection or θ
i
=θ
r
For flat mirrors, images of objects are upright and the same distance behind the
mirror as the objects are in front of the mirror. The image size is the same as the

object size. Image is always virtual. For mirrors with curved surfaces, images can be
greater than or less than objects. An inverted image is virtual or real. And the real
image can be projected onto a screen.



REFRACTION
When light travels from one medium into another medium, its path is bent, the
light is refracted. Refraction occurs when the second substance has a different density
from the first, so that the speed of light in two substances differs. In this case, if the
light ray does not enter perpendicular to the second surface, it will change direction at
the interface where the two surfaces meet. The resulting refraction of the light ray can
be described clearly by Snell’s law, as following:
1 1 2
2 2 1
sin
sin
v n
v n


 

or
1 1 2 2
sin sin
n n
 


Or in the words, when a light ray passes from one medium to another, the ratio
between the sine of the angle of incidence and the sine of the angle of refraction is
constant.
From the laws of reflection and refraction, we can determine the behavior of
optical devices such as telescopes and microscopes. We can draw the paths of
different rays through the optical system and see how images can be formed, their
relative orientation, and their magnification. This is in fact the most important use of
geometrical optics to this day: the behavior of complicated optical system can be
determined by studying the paths of all rays through the system.

Lenses
A lens is an optical device which transmits and refracts light, converging or
diverging the beam. Because of the curvature of a lens’s surfaces, when an incident
light beam comes, its different rays are refracted through different angles. A simple
lens is a lens consisting of a single optical element. Most of lenses are typically made
of glass or transparent plastic.
A beam of parallel rays can be caused to converge at a single point or diverge
from a single point. This point is called the focal point of the lens. If the light rays
converge when they pass through a lens, a real image is formed. We can see the real
image on a screen. If the light rays diverge after passing through the lens, a virtual
image is formed, and we cannot see this image on a screen, it is visible only when we
look into the lens. The ratio of size of the image and size of the object depends on the
focal length of the lens ( the distance between the focal point and the center of the
lens), and on the distance between the lens and the object.
Lenses can be divided into two kinds: convex lenses or concave lenses.
A convex lens is a converging lens. This kind of lens is thicker in the middle
and thinner towards the edges, like the lens in a magnifying glass. The image is
changed by the position of the object in relation to the focal length and the radius of
curvature. If the object is beyond 2F, the image is real, inverted and reduced, at 2F

real, inverted and the same height, between F and 2F real, inverted, and magnified, at
F there is no image, and in front of F, the image is virtual, erect, and magnified.
A concave lens is thicker towards the edges and thin in the middle. Lenses
bend light rays so that they diverge, and so produce only virtual images. The image is
formed on the same side of the lens as the object, it is upright and is always smaller
than the real object. The size of the image is controlled by the distance of the object
from the lens: the closer the object is to the lens, the larger the image is.

Mirror
Mirrors work much like lenses, except that they have reflective surfcaces.
Mirrors can be convex or concave and there are also plane mirrors. Every mirror has
a focal point, where all the light directed at that mirror converges or diverges. The
distance between the mirror and the focal point is called the focal length. The radius
of the curvature of a mirror is exactly twice the focal length. Mirrors can create both
real which we can see on a screen,and virtual images which can be seen when we
look into the mirror. Images are also either inverted or erect, upside down or right
side up respectively. The focal length is referred to as F and the radius of curvature
2F. The magnification of any mirror can be calculated by subtracting the ratio of the
height of the image to the height of the object and the ratio of the distance from the
mirror of the image to the distance of the object. If the result is a negative number,
then it represents the factor of reduction as opposed to the factor of magnification.
A concave mirror is a converging mirror which works much like a convex lens.
A concave mirror bends further away in the middle than at the edges, like the inside
of bowl. The image produced depends on the distance between the object and mirror.
If the object is beyond 2F, the image is real, inverted, and reduced. If it is at 2F, the
image is real, inverted, the same height. If it is between F and 2F, the image is real,
inverted, and magnified. If it is at F, there is no image, and if it is closer then F, the
image is virtual, erect, and magnified.
A convex mirror is opposite to a concave mirror. It is a diverging mirror and
works like a concave lens. It bends further away at the edges than in the middle like

the outside of a bowl. Convex mirrors always produce virtual, erect, reduced images.
Plane mirrors are simple straight up mirrors. In a plane mirror, the image is
always virtual and the same size as the object.

Dispersion
Dispersion is the phenomenon in which the phase velocity of a wave depends
on its frequency, or alternatively when the group velocity depends on the frequency.
This phenomenon can be described as following: When a ray of white light travels
from air into a triangular glass prism, the light not only bends but also is separated
into its component colors, the colors of the spectrum. The violet light is bent slightly
more than the red because it travels more slowly through the glass. As the light
emerges from the prism the colors separate even more.
The most example of dispersion is probably a rainbow. We can see the rainbow
because the sunlight is refracted and dispered by water droplets in the atmosphere.
You can also observe a lot of different dispersion in the nature.

Total Internal Reflection
Total internal reflection is an optical phenomenon that occurs when a ray of
light travels from a dense to a less dense medium with the condition: the light strikes
the interface at a large enough angle, called the critical angle. If the refractive index is
lower on the side of the boundary, no light can pass through and all of light is
reflected. The critical angle is the angle of incidence above which the total internal
reflection occurs. It depends on the relative indexes of refraction of the two medium.
We can describe the total internal reflection as: When the light beam crosses a
boundary between materials with different refractive indices, a part of it will be
refracted at the boundary surface, and a remaining part will be reflected. If the angle
of the incidence is greater than the critical angle, the light will stop crossing the
boundary altogether and instead be totally reflected back internally. This can only
occur when light travels from a medium with a higher refractive index to one with a
lower refractive index. For example, it will only occur when passing from glass to air,

but cannot occur when passing from air to glass.
In daily life, we can observe total internal reflection while swimming, if we
open our eyes just under the water’s surface. We ourselves can do experiments to
represent this phenomenon.

Physical Optics
Looking again at the ray picture of focusing above, we run into a problem: at
the focal point, the rays all intersect. The density of rays at this point is therefore
infinite, which according to geometrical optics implies an infinitely bright focal spot.
Obviously, this cannot be true.
If we put a black screen in the plane of the focal point and look closely at the
structure of the focal spot projected on the plane, experimently we would see a very
small central bright spot, but also much fainter rings surrounding the central spot.
These rings cannot be explained by using the geometrical optics alone, and result
from the wave nature of light. This leads the conclusion: light has wavelike
properties. The conclusion was demonstrated by scientists such as Thomas Young,
Josef Fraunhofer and Augustin Fresnel, with their theories and experiments. And the
field of physical optics was born.
Physical optics studies the wave properties of light, which may be grouped into
three categories: interference, diffraction, and polarization. Inteference is the ability
of a wave to interfere with itself, creating extremely bright and extremely dark
regions. Differaction is the ability of waves to bend around corners and spread after
passing through an apterture. Polarrization refers to properties of light related to its
transverse nature.
We can use three categories of physical optics to explain phenomena in the
nature. Example, the sun appears red, the sky appears blue ( use diffraction), the
production of three-dimensional images ( use interference).

Chapter 5: Atomic particles and nuclear physics.

Atomic Particles
We are living in this universe. But we do not understand fully about it.
Scientists have tried to describe, understand clearly it, to give a unified picture of
natural phenomena. Before the 1970s there were thought to be four main forces in
nature, and two of them could not be mathematically define. In the late 1980s
scientists devised a hypothesis about the existence of a fifth fundermental force in
nature. And in the early 1990s, by experiments, they concluded exactly the existence
of a fifth fundermental force. In addition, scientists have developed techniques to
probe more deeply into structure of matter and to break down matter into its most
basic elements. Following the modern atomic theory, atoms consists of electrons and
nucleus. The nucleus is made of neutrons and protons.
Today, scientists show that all the matter in the universe is viewed as being
composed of three kinds of elementary particles. They include:
- Six flavours quarks: up, down, bottom, top, strange, and charm.
- Six types of leptons: electron, electron neutrino, muon, muon nertrino, tauon,
tauon nertrino.
- Twelve gauge bosons ( force carriers): the photon of the electromagnetism,
the three W and Z bosons of the weak force, and the eight gluons of the strong force.
Composite subatomic particles (such as protons or atomic nuclei) are bound
states of two or more elementary particles. For examples, a proton is made of two up
quarks and one down quark, while the atomic nuclei of helium-4 is composed of two
protons and two neutrons. Composite particles include all hardrons, a group
composed of baryons and mesons.
There are hundreds of known subatomic particles, and most are result of
cosmic rays interacting with matter, or have been produced by scattering processes in
particle accelerators.

Nuclear Physics
Nuclear physics is the field of physics. It deals with the study of the properties
of nuclei and of their relationship to the fundamental constituents and laws of nature.

It has applications in the generation of electrical power, in the treatment of cancer and
other diseases, and in the developmnet of nuclear weapons, among many others. Its
applications have been a major influence in the course of human history.
When studying nuclear physics, we must note to nuclear energy, an important
source of energy now and in the future. The energy that the sun and stars radiate is
the result of nuclear reactions, in which matter is coverted to energy. Presently,
nuclear energy provides for approximately 16% of the world’s electricity. Unlike the
stars, the nuclear reactors that we have today work on the principle of nuclear fission.
Scientists are working to make fussion reators which have the potential of providing
more energy with fewer disadvantages than fission reactors.
Changes which occur in the structure of the nuclei of atoms are called nuclear
reactions. And energy created in a nuclear reaction is called nuclear energy, or atomic
energy. Nuclear energy is produced naturally and in man-made operations under
human control.
- Naturally: for example the Sun and other stars
- Man-made: nuclear energy is produced by machines called nuclear reactors,
parts of nuclear power plants. They provide electricity for many cities.
Man-made nuclear reactions also occur in the explosion of atomic and
hydrogen bombs.
Nuclear energy has advantages and disadvantages. Its advantages incluce:
- The Earth has limited supplies of coal and oil. Nuclear power plants
could still produce electricity after coal and oil become scarce.
- Nuclear power plants need less fuel than ones which burn fossil fuels. One
ton of uranium produces more energy than is produced by several million
tons of coal or several million barrels of oil.
- Coal and oil burning plants pollute the air. Well-operated nuclear power
plants do not release contaminants into the environment.
Disadvantages of nuclear energy inclue:
- Nuclear explosions produce radiation. The nuclear radiation harms the cells
of the body which can make people sick or even kill them. Illness can strike

people years after their exposure to nuclear radiation.
- One possible type of reactor disaster is known as a meltdown. In such an
accident, the fission reaction goes out of control, leading to a nuclear
explosion and the emission of great amounts of radiation.
- Nuclear reactors also have waste disposal problems. Reactors produce
nuclear waste products which emit dangerous radiation. Because they could
kill people who touch them, they cannot be thrown away like ordinary
garbage. Currently, many nuclear wastes are stored in special cooling pools
at the nuclear reactors.
-


 Nuclear explosions produce radiation. The nuclear radiation harms
the cells of the body which can make people sick or even kill them.
Illness can strike people years after their exposure to nuclear
radiation.
 One possible type of reactor disaster is known as a meltdown. In
such an accident, the fission reaction goes out of control, leading to a
nuclear explosion and the emission of great amounts of radiation.
 In 1979, the cooling system failed at the Three Mile Island
nuclear reactor near Harrisburg, Pennsylvania. Radiation
leaked, forcing tens of thousands of people to flee. The
problem was solved minutes before a total meltdown would
have occurred. Fortunately, there were no deaths.
 In 1986, a much worse disaster struck Russia's Chernobyl
nuclear power plant. In this incident, a large amount of
radiation escaped from the reactor. Hundreds of thousands of
people were exposed to the radiation. Several dozen died
within a few days. In the years to come, thousands more may
die of cancers induced by the radiation.

 Nuclear reactors also have waste disposal problems. Reactors
produce nuclear waste products which emit dangerous radiation.
Because they could kill people who touch them, they cannot be
thrown away like ordinary garbage. Currently, many nuclear wastes
are stored in special cooling pools at the nuclear reactors.
 The United States plans to move its nuclear waste to a remote
underground dump by the year 2010.
 In 1957, at a dump site in Russia's Ural Mountains, several
hundred miles from Moscow, buried nuclear wastes
mysteriously exploded, killing dozens of people.
 Nuclear reactors only last for about forty to fifty years.
The Future of Nuclear Energy
Some people think that nuclear energy is here to stay and we must learn to
live with it. Others say that we should get rid of all nuclear weapons and
power plants. Both sides have their cases as there are advantages and
disadvantages to nuclear energy. Still others have opinions that fall
somewhere in between.
What do you think we should do? After reviewing the pros and cons, it is
up to you to formulate your own opinion. Read more about the politics of
the issues or go to the forum to share your own opinions and see what
others think.