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zPhysics
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, medicinedepend 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 foudation 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 law 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 techelogy.
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 reggard to the forces present. It is
simply a mathematical way to describe motion.
Three Newton’s law:
Classical mechanics is governed by three basic principles, which were first
formulated in the 17th and 18th centuries by Isaac Newton. These principles are
known as Newton’s law.
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: the
relationship between an object’s mass m, its acceleration a, and the applied force F is
F=ma. 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 2nd 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 cuase 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 show the
change in velocity of a body in a unit time. According to Newton’s 2nd 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 see 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 cosa
Where F is the force, d is the distance through which the force acts (the
displacement), a is 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)mv2
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 regions 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 can 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 importan 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 fuelreact 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 raio of
one to one.
The second law: Heat transfer happens spontaneosly 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 body, 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 raise, 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 desity
(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 varietyof 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. Hower 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 18th
ceturies, 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 18th 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 19th
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 copass
near a current carrying wire, its magnetized needle would realign. If the current is
reversed in direction, the compass needle reverse it 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 righthand 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 investigateed 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 raybased 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 mirro 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
θi, and the angle at which it bounces off, called the angle of reflection θr. We always
have θi =θr . 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:
1. The incident ray, the reflected ray and the normal to the reflection surface at
the point of the incidence lie in the same plane.
2. The angle of incidence equals the angle of reflection or θi =θr
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:
sin 1 v1 n2
 
sin  2 v2 n1
or
n1 sin 1  n2 sin 2
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.
In optics, dispersion is the phenomenon in which the phase velocity of a wave
depends on its frequency,[1] or alternatively when the group velocity depends on the
frequency. Media having such a property are termed dispersive media. Dispersion is
sometimes called chromatic dispersion to emphasize its wavelength-dependent
nature, or group-velocity dispersion (GVD) to emphasize the role of the group
velocity.
The most familiar example of dispersion is probably a rainbow, in which dispersion
causes the spatial separation of a white light into components of different
wavelengths (different colors). However, dispersion also has an effect in many other
circumstances: for example, GVD causes pulses to spread in optical fibers, degrading
signals over long distances; also, a cancellation between group-velocity dispersion
and nonlinear effects leads to soliton waves. Dispersion is most often described for
light waves, but it may occur for any kind of wave that interacts with a medium or
passes through an inhomogeneous geometry (e.g. a waveguide), such as sound waves.
There are generally two sources of dispersion: material dispersion and waveguide
dispersion. Material dispersion comes from a frequency-dependent response of a
material to waves. For example, material dispersion leads to undesired chromatic
aberration in a lens or the separation of colors in a prism. Waveguide dispersion
occurs when the speed of a wave in a waveguide (such as an optical fiber) depends on
its frequency for geometric reasons, independent of any frequency dependence of the
materials from which it is constructed. More generally, "waveguide" dispersion can
occur for waves propagating through any inhomogeneous structure (e.g. a photonic
crystal), whether or not the waves are confined to some region. In general, both types
of dispersion may be present, although they are not strictly additive. Their
combination leads to signal degradation in optical fibers for telecommunications,
because the varying delay in arrival time between different components of a signal
"smears out" the signal in time.
2. 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, experimentally we would see an
image as simulated below:
There is a very small central bright spot, but also much fainter (augmented in this
image) rings surrounding the central spot. These rings cannot be explained by the use
of geometrical optics alone, and result from the wave nature of light.
Though people had long suggested that light has wavelike properties, direct evidence
was lacking (note the size of the focal spot in the picture above: the rings are quite
difficult to see with the naked eye) until the early 1800s. A number of scientists
provided the theoretical and experimental framework to demonstrate that light has
wavelike properties, notable among them Thomas Young, Josef Fraunhofer and
Augustin Fresnel. From this work, the field of physical optics was born.
Physical optics is the study of the wave properties of light, which may be roughly
grouped into three categories: interference, diffraction, and polarization. Interference
is the ability of a wave to interfere with itself, creating localized regions where the
field is alternately extremely bright and extremely dark. Diffraction is the ability of
waves to ‘bend’ around corners and spread after passing through an aperture.
Polarization refers to properties of light related to its transverse nature. We will cover
all these terms in more detail in subsequent posts.
The wave nature of sound can be readily determined by anyone even without special
scientific apparatus. For instance, if you stand on the opposite side of a building from
a friend, out of direct line of sight, your friend’s shouts will still be audible to you.
The sound waves from your friend partially wrap around the corners of the building,
allowing you to hear him or her. This may be considered an example of diffraction.
The wave nature of light is not as readily apparent. The reason for this discrepancy
has to do with the wavelength of the waves in each case. For our purposes, the
wavelength may be considered a distance over which wave effects are typically
apparent. For audible sound, wavelengths range from millimeters to 20 meters, while
for visible light the wavelength is on the order of 0.0000005 meters, much smaller
than can be observed with the human eye.
. The angle through which the light is refracted depends, according to Snell's
law, on the indices of refraction of both the first and second media. The index of
refraction of a medium is a property of the material that can be measured by
laboratory experiments.
http://en.wikipedia.org/wiki/Snell%27s_law
. Refraction can be seen when looking into a bowl of water. Air has a refractive
index of about 1.0003, and water has a refractive index of about 1.33. If a person
looks at a straight object, such as a pencil or straw, which is placed at a slant,
partially in the water, the object appears to bend at the water's surface. This is due to
the bending of light rays as they move from the water to the air. Once the rays reach
the eye, the eye traces them back as straight lines (lines of sight). The lines of sight
(shown as dashed lines) intersect at a higher position than where the actual rays
originated. This causes the pencil to appear higher and the water to appear shallower
than it really is. The depth that the water appears to be when viewed from above is
known as the apparent depth. This is an important consideration for spearfishing
from the surface because it will make the target fish appear to be in a different place,
and the fisher must aim lower to catch the fish.
The diagram on the right shows an example of refraction in water waves. Ripples
travel from the left and pass over a shallower region inclined at an angle to the
wavefront. The waves travel more slowly in the shallower water, so the wavelength
decreases and the wave bends at the boundary. The dotted line represents the normal
to the boundary. The dashed line represents the original direction of the waves. This
phenomenon explains why waves on a shoreline tend to strike the shore close to a
perpendicular angle. As the waves travel from deep water into shallower water near
the shore, they are refracted from their original direction of travel to an angle more
normal to the shoreline.[1] Refraction is also responsible for rainbows and for the
splitting of white light into a rainbow-spectrum as it passes through a glass prism.
Glass has a higher refractive index than air. When a beam of white light passes from
air into a material having an index of refraction that varies with frequency, a
phenomenon known as dispersion occurs, in which different coloured components of
the white light are refracted at different angles, i.e., they bend by different amounts at
the interface, so that they become separated. The different colors correspond to
different frequencies.
While refraction allows for beautiful phenomena such as rainbows, it may also
produce peculiar optical phenomena, such as mirages and Fata Morgana. These are
caused by the change of the refractive index of air with temperature.
Recently some metamaterials have been created which have a negative refractive
index. With metamaterials, we can also obtain total refraction phenomena when the
wave impedances of the two media are matched. There is then no reflected wave.[2]
Also, since refraction can make objects appear closer than they are, it is responsible
for allowing water to magnify objects. First, as light is entering a drop of water, it
slows down. If the water's surface is not flat, then the light will be bent into a new
path. This round shape will bend the light outwards and as it spreads out, the image
you see gets larger.
A useful analogy in explaining the refraction of light would be to imagine a marching
band as they march at an oblique angle from pavement (a fast medium) into mud (a
slower medium). The marchers on the side that runs into the mud first will slow down
first. This causes the whole band to pivot slightly toward the normal (make a smaller
angle from the normal).
The Kinetic Theory of Matter states that matter is composed of a large number a small particles--individual atoms or
molecules--that are in constant motion. This theory is also called the Molecular Theory of Matter. By making some
simple assumptions, the theory helps to explain the behavior of matter, especially the flow or transfer of heat and the
relationship between pressure, temperature and volume properties of gases.