Download Modern physics

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• Sketch a graph that correctly relates the
speed of an EM wave in a medium to the
index of refraction for that medium. Show
work.
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v
Modern Physics
1. Wave-Particle Duality of Energy and
Matter
2. Models of Atoms
3. The Nucleus
4. The Standard Model of Particle Physics
1. Wave-Particle Duality of Energy and Matter
objectives
• Know:
– Definitions of photon and Planck’s Constant.
• Understand:
– The manner in which the Photoelectric Effect
demonstrates the particle nature of light.
• Be able to:
– Determine the energy of a photon based on its
frequency and/or wavelength.
– Determine a photon’s ‘type’ using the EM Spectrum
chart.
– Use/interpret a graph of photon energy vs. frequency
and/or frequency vs. wavelength.
• Homework – castle learning
Light as a wave
•
•
Light is an electromagnetic wave produced by an oscillating
electric charges
_______________________.
The vibrating charges produce
alternating _________________________________which
are
electric and magnetic fields
perpendicular to the direction of the wave’s motion. This waves
can travel through vacuum in vast space.
Light is a wave because
1. Light have wave characteristics such as
amplitude, wavelength, frequency, and velocity.
_________________________________________________
2. Light exhibit wave behavior such as
diffraction, interference, and the Doppler effect.
_________________________________________________
•
However, the wave model of light can not explain interactions
of light with matter
An unusual phenomenon was discovered in
the early 1900's. If a beam of light is pointed
at the negative end of a pair of charged
An unusual phenomenon was discovered
plates, a current flow is measured. A current
in the early 1900's.
is simply a flow of electrons in a metal, such
asPhotoelectric_Effect
a wire. Thus, the beam of light must be
liberating
electrons
one metal
If a beam
of lightfrom
is pointed
at plate,
the
which
are attracted
the of
other
plate by
negative
end of atopair
charged
plates, a
electrostatic
forces.
This resultswhich
in a current
current flow
is measured
means
flow.
the beam of light must be liberating
Waves have a particle nature
electrons from one metal plate, which are
attracted to the other plate by electrostatic
forces.
However, the observed phenomenon was
that the current flow varied strongly with
the frequency of light such that there was
a sharp cutoff and no current flow for
smaller frequencies. Only when the
frequency is above a certain point
(threshold frequency), the current flow
increases with light strength.
Photoelectric Effect
Einstein explains photoelectric effect
• ..\..\RealPlayer Downloads\Photoelectric Effect and
Photoelectric Cell.flv
• Einstein successful explained the photoelectric effect within the
context of the new physics of the time, quantum physics
developed by Max Planck.
• Quantum theory assumes that electromagnetic energy is emitted
from and absorbed by matter in discrete amounts of packets.
Each packet carries a quantum of energy.
• The quantum, or basic unit, of electromagnetic energy is called
a photon. A photon is a mass-less particle of light, it carries a
quantum of energy.
Energy: E = h∙f
Energy: E = h∙f
• since f = c/λ
E = h∙f = h∙c/λ
• The amount of energy E of each photon is directly proportional to
the frequency f of the electromagnetic radiation, and inversely
proportional to the wavelength λ.
– E is energy of a photon, in Joules, or eV,
– 1 eV = 1.60x10-19 J
– h is Planck’s constant, 6.63 x 10-34 J∙s
– f is frequency of the photon, in hertz
– c is the speed of light in vacuum, c = 3.00x108 m/s
– λ is wavelength, in meters
E
E
Direct relationship
Slope = h
f
Inverse relationship
λ
The Compton effect: photon-particle
collision
• In 1922 Arthur Compton was
able to bounce an X-ray photon
off an electron. The result was
an electron with more kinetic
energy than it started with, and
an X-ray with less energy than it
started with. A photon can
actually interact with a
particle! A photon has
momentum!! - another proof
that photon is a particle.
• During the collision, both
energy and momentum are
conserved.
The momentum of a photon
• A photon, although mass-less, it has momentum as well as
energy. All photons travel at the speed of light, c. The
momentum of photon is
p = h/λ = h∙f/c
Where
p is momentum,
h is plank’s constant,
λ is the wavelength
• Momentum p is directly proportional to the frequency light,
and inversely proportional to the wavelength.
p = h/λ = h∙f/c
E = hc/λ = h∙f
• In conclusion, light has both wave and particle nature.
• Wave nature:
– Exhibit wave characteristics:
wavelength,
frequency, crests, troughs, amplitude …
_______________________________________________________
– Exhibit wave behavior:
interference, diffract, Doppler effect, refract, reflect …
– _______________________________________________
• Particle nature:
Photoelectric effect
– ________________________________________
– _________________________________
Interact with electron – has momentum
Reflect like a particle
– _________________________________
Particles have wave nature
• Just as radiation has both wave and particle characteristics,
matter in motion has wave as well as particle characteristics.
• The wavelengths of the waves associated with the motion of
ordinary object is too small to be detected.
• The waves associated with the motion of particles of atomic or
subatomic size, such as electrons, can produce diffraction and
interference patterns that can be observed.
• ..\..\RealPlayer Downloads\Double Slit Experiment - The
Strangeness Of Quantum Mechanics.flv
All Matters have wave nature
• All matters have wave nature.
• Louis de Broglie (French physicist and a Nobel
laureate) assumed that any particle--an electron, an
atom, a bowling ball, whatever--had a "wavelength" that
was equal to Planck's constant divided by its
momentum...
λ=h/p
..\..\RealPlayer Downloads\Matter Wave - De Broglie
Wavelength.flv
In summary
• Waves has particle nature, it has
momentum just like a particle:
p=h/ λ
• Particle has wave nature, it has a
wavelength just like a wave:
λ=h/p
Example
1. Which graph best represents the relationship
between the intensity of light that falls on a
photo-emissive surface and the number of
photoelectrons that the surface emits?
a
b
c
d
Note: this only happens when the frequency of the light
beam is above a certain point
Example
2.
When the source of a dim orange light shines on a
photosensitive metal, no photoelectrons are ejected from its
surface. What could be done to increase the likelihood of
producing photoelectrons?
a. Replace the orange light source with a red light source.
b. Replace the orange light source with a higher frequency
light source.
c. Increase the brightness of the orange light source.
d. Increase the angle at which the photons of orange light
strike the metal.
Example
3. A beam of monochromatic light incident on a metal surface
causes the emission of photoelectrons. The length of time
that the surface is illuminated by this beam is varied, but
the intensity of the beam is kept constant. Which graph
below best represents the relationship between the total
number of photoelectrons emitted and the length of time of
illumination?
a
b
c
d
Class work
• Worksheet 6.1.1 #1, 3, 5-9, 11
• Review questions #1-11
5/5 do now
• In which medium is the wavelength of
yellow light the shortest? [show work]
A.Flint glass
B.Crown glass
C.Diamond
D.zircon
2. Models of an Atom objectives
1. Describe Thompson’s model
2. Explain the strengths and weaknesses of
Rutherford’s model of the atom
3. Describe Bohr model of an atom
4. Describe cloud model
5. Explain why only certain energy levels
are permitted in atoms.
Homework: castle learning
• About 440BC, a Greek scientist named Democritus came up with
the idea that eventually, all objects could be reduces to a single
particle that could not be reduced any further.
He called this particle an atom, from the Greek word atomos
which meant “not able to be divided.”
From this, the idea of the atom – the basic building block of all
matter – was born.
• Around 1700, scientists understanding of molecular composition of
matter had grown considerably. They had figured out that elements
combine together in specific ratios to form compounds. In 1803,
British chemist John Dalton came up with a theory about atoms:
– All substances are made of small particles that can’t be created,
divided, or destroyed called atoms.
– Atoms of the same element are exactly alike, and atoms of
different elements are different from each other. (So, atoms of
gold are exactly like gold atoms, but different than aluminum
atoms).
– Atoms join with other atoms to make new substances.
Thompson’s model
• In 1897, a British scientist named JJ
Thomson discovered that electrons are
relatively low-mass, negatively charged
particles present in atoms.
• Because atoms are neutral, he proposed a
model - the "atom" was made of
negatively-charged particles (electrons)
dispersed among positively-charged
particles (protons) like raisins in "plums
in a pudding".
• In 1909, British scientist Ernest Rutherford decided to test the
Thomson theory, and designed an experiment to examine the
parts of an atom.
Rutherford’s model
• In his experiment, He fired alpha particles (2 positive charges) beam
at extremely thin gold foil.
• He expected alpha particles travel in straight line unaffected because
the net electric force on the alpha particle would be relatively small.
• However, he found a small number of particles were scattered at large
angles.
• Rutherford explained this phenomenon by assuming the following:
– Most particles were not affected due to the vast empty space
inside the atom
– Only a few particles were scattered due to the repulsive force
between the concentrated positive charge inside the atom and the
particle.
• Rutherford’s model of the atom
– most of the mass was concentrated into a compact nucleus
(holding all of the positive charge), with electrons occupying the
bulk of the atom's space and orbiting the nucleus at a distance.
• In Rutherford’s model of the atom,
electrons orbit the nucleus in a manner
similar to planets orbiting the sun.
Limitation of Rutherford model
• According to Rutherford, electrons
accelerate due to centripetal force, and
the accelerating charges radiate
electromagnetic waves, losing energy. So
the radius of electron’s orbit would steadily
decrease.
• This model would lead a rapid collapse of
the atom as the electron plunged into the
nucleus.
The Bohr Model of the hydrogen atom
•
Danish physicist Niels Bohr attempted to explain the problems in
Rutherford’s model. He proposed in 1913 that electrons move
around the nucleus of an atom in specific paths, on different
levels of energy.
1. All forms of energy are quantized.
2. The electron in an atom can occupy only
certain specific orbits and no other.
3. Electrons can jump from one orbit to another
by emitting or absorbing a quantum of
energy in the form of photon.
4. Each allowed orbit in the atom corresponds to
a specific energy level. The orbit nearest the
nucleus represents the smallest amount of
energy that the electron can have. The
electron can remain in this orbit with out
losing energy even though it is being
accelerated.
• When electron is in any particular orbit, it is said to
be in a stationary state. Each stationary state
represents an energy level. The successive
energy levels of an atom are assigned integral
numbers, denoted by n=1, 2, 3…
• When the electron is in the
lowest level (n=1), it is said
to be in the ground state.
• For a hydrogen atom, an
electron in any level above
the ground state is said to
be in an excited state.
• When electron goes up from lower to higher
level, the atom absorbs a quantum of energy in
the form of a photon.
• When electron goes down from higher to lower
level, the atom emits a quantum of energy in the
form of a photon.
• If the energy of the photon of light is just right, it will cause
the electron to jump to a higher level.
• When the electron jumps back down, a photon is emitted for
each jump down.
• A photon without the right amount of energy (the pink one)
passes through the atom with no effect.
• Photons with too much energy will cause the electron to be
ejected which ionizes the atom
Energy levels
• excitation: any process that raises the energy level of
electrons in an atom.
• Excitation can be the result of absorbing the energy
of colliding particles of matter, such as electrons, or
of photons of electromagnetic radiation.
• A photon’s energy is absorbed by an electron in an
atom only if the photon’s energy corresponds exactly
to an energy-level difference possible for the
electron.
• Excitation energies are different for different atoms.
Ionization potential
• An atom can absorb sufficient energy to
raise an electron to an energy level such
that the electron is removed from the
atom’s bound and an ion is formed.
• The energy required to remove an electron
from an atom to form an ion is called the
atom’s ionization potential.
• An atom in an excited state requires a
smaller amount of energy to become an
ion than does an atom in the ground state.
Energy level diagram
ionization
Ground state
• The energy level of an
electron that has been
completely removed
from the atom is
defined to be 0.00 eV.
All other energy levels
have negative values.
• The electron in the
ground state has the
lowest energy, with
largest negative value.
Ephoton = Einitial - Efinal
Ephoton = hf
where h = 6.63 x 10-34
• This formula can be used
to determine the energy
of the photon emitted (+)
or absorbed(-).
• This formula can be used
to determine the energy
of a photon if you know
the frequency of
it. Planck's constant, h,
Js
can be used in terms of
Joule(s) or eV(s).
(note: the Regents
reference table only gives
it in terms of Js)
Energy level is explained by Louis de
Broglie’s particle-wave theory
• ..\..\RealPlayer Downloads\Matter Wave - De Broglie
Wavelength.flv
• According to de Broglie, particles have wave nature:
λ=h/p
• If we begin to think of electrons as waves, we'll have to change
our whole concept of what an "orbit" is. Instead of having a
little particle whizzing around the nucleus in a circular path,
we'd have a wave sort of strung out around the whole circle.
Now, the only way such a wave could exist is if a whole
number of its wavelengths fit exactly around the circle.
• If the circumference is exactly as long as two wavelengths, say,
or three or four or five, that's great, but two and a half won't cut
it.
..\..\RealPlayer Downloads\Quantum Mechanics- The Structure Of Atoms.flv
Limitations of Bohr’s model
• It can not predict or explain the electron
orbits of elements having many electrons
• ..\..\RealPlayer Downloads\Quantum
Mechanics.flv
The cloud model (Schrödinger model)
• In this model, electrons are not confined to specific orbits,
instead, they are spread out in space in a form called an electron
cloud.
• The electron cloud is densest in regions where the probability of
finding the electron is highest.
The cloud model represents a sort
of history of where the electron has
probably been and where it is likely
to be going.
example
•
The diagram represents alpha particle A
approaching a gold nucleus. D is the
distance between the path of the alpha
particle and the path for a head-on
collision. If D is decreased, the angle of
deflection θ of the alpha particle would
1. decrease
2. increase
3. remain the same
example
•
A.
B.
C.
D.
Which diagram shows a possible path of an
alpha particle as it passes very near the
nucleus of a gold atom?
1
2
3
4
example
•
1.
2.
3.
4.
In Rutherford's model of the atom, the
positive charge
is distributed throughout the atom's
volume
revolves about the nucleus in specific
orbits
is concentrated at the center of the atom
occupies most of the space of the atom
Class work
• Worksheet 6.1.1 #1, 3, 5-9, 11
• Review questions #1-11
• Review questions #12-19
5/6 do now
• When a ray of light traveling in water reaches a
boundary with air, part of the light ray is
reflected and part is refracted. Which ray diagram
best represents the paths of the reflected and
refracted light rays?
A
B
C
D
Atomic spectra
1. Explain atomic spectra using Bohr’s
model of the atom.
2. Recognize that each element has a
unique emission and absorption
spectrum.
Atomic spectra
• According to Bohr’s model, electrons in atoms
can be found in only certain discrete energy
states.
Atomic spectra
• When electrons jump from the lower to the higher number orbits,
they absorb a particular amount of energy and we can observe
the absorption spectrum.
• When they fall back again they release the same amount of
energy and we can observe the emission (bright-line) spectrum.
The amount of energy absorbed or released in this way can be
directly related to the wavelength at which we see the absorption
and emission lines on the spectrum.
• Each element has a characteristic
spectrum that differs from that of every
other element.
• The emission spectrum can be used to
identify the element, even when the
element is mixed with other elements.
Hydrogen spectrum
Helium spectrum
Emission (bright-line, atomic)
spectra
• In a hot gas, when an electron in an atom
in an excited state falls to a lower energy
level, the energy of the emitted photon is
equal to the difference between the
energies of the initial and final states.
Ephoton = Ei – Ef = hf
• Ei is the initial energy of the electron in its
excited state and Ef is the final energy of
the electron in the lower energy level.
• Each energy difference between two energy
levels corresponds to a photon having a specific
frequency.
For example: An electron in a hydrogen atom
drops from the n = 3 energy level to the n = 2
energy level. The energy of the emitted photon
is
Ephoton = E3 – E2 = (-1.51 eV) – (-3.40 eV) = 1.89 eV
Ephoton = 1.89 eV x 1.60 x 10-19 J/eV = 3.02 x 10-19 J
Using Ephoton = hf, we can find the frequency of the emitted
photon:
f = 3.02 x 10-19 J / (6.63x10-34 J∙s) = 4.56 x 1014 Hz which
corresponding to red light
A specific series of
frequencies,
characteristic of the
element, is produced
when the electrons of its
atoms in excited states
fall back to lower states
or to the ground state.
When these emitted
frequencies appear as a
series of bright lines
against a dark
background, they are
called a bright-line
spectrum or an
emission spectrum.
Absorption spectra
• In a cold gas, an atom can absorb only
photons having energies equal to specific
differences in its energy levels.
• The frequencies and wavelengths of these
absorbed photons are exactly the same as
those of the photons emitted when
electrons lose energy and fall between the
same energy levels.
Example
1. An electron in a hydrogen atom drops from the
n = 4 energy level to the n = 2 energy level.
The energy of the emitted photon is
Ephoton =Ei – Ef
Ephoton =(-0.85eV)–(-3.40eV)
Ephoton =2.55 eV
Ephoton =4.08 x 10-19 J
example
2.
A.
B.
C.
D.
Excited hydrogen atoms are all in the n = 3 state. How
many different photon energies could possibly be
emitted as these atoms return to the ground state?
1
2
3
4
3. The Nucleus Objectives
Know:
•
Energy/mass relationship equation.
Understand
•
The connection between energy and mass and the fact
that energy and mass can be converted into one
another.
Be able to
•
Determine the energy contained in a given amount of
mass.
•
Convert universal mass units into MeV.
•
Use/interpret a graph of energy vs. mass.
The Nuclear Force
• The nucleus is the core of an atom made up of one or
more protons (except for one of the isotopes of
hydrogen) and one or more neutron. The positively
charged protons in any nucleus containing more than
one proton are separated by a distance of 10-15 m.
• In the nucleus, there are two major forces:
– A large repulsive electric (Coulomb) force between
protons
– A very strong attractive nuclear force to keep the
protons together.
• It is this nuclear force inside a nucleus that overcomes
the repulsive electric force between protons and hold the
nucleus together.
Nuclear force has rather unusual properties.
1. It is charge independent. This means that in all pairs
neutron & neutron, proton & proton, and neutron &
proton, nuclear forces are the same.
2. at distances 10-13 cm, the nuclear force is attractive
and very strong, 100 times stronger than the
electromagnetic repulsion. Strongest forces known to
exist, nuclear force is also called strong force.
3. the nuclear force very short range force. At distances
greater than a few nucleon diameters, the nuclear
attraction practically disappears. As the nucleus gets
bigger, the attractive nuclear force between the nucleons gets
smaller, the nucleus becomes very unstable and starts to break
apart, causing radioactive decay.
Universal mass unit
• The universal mass unit, or atomic mass unit, is defined as
1/12 the mass of an atom of carbon-12, which is a carbon
atom having 6 protons, 6 neutrons, and 6 electrons.
• In universal mass unit,
– the mass of the proton is 1.0073 u,
– the mass of the neutron is 1.0087 u,
– the mass of an electron is 0.0005 u.
• In SI units, a mass of one universal mass unit,
1 u = 1.66 x 10-27 kg.
Mass-energy relationship
• Einstein showed that mass and energy are
different forms of the same thing and are
equivalent.
E = mc2
• E is energy in joules,
• m is mass in kg,
• c is the speed of light in vacuum 3.00x108
m/s
Nuclear mass and energy
• According to Einstein’s mass-energy equation,
any change in energy results in an equivalent
change in mass. Mass-energy is conserved at
all levels from cosmic to subatomic.
• In chemical reactions, if energy is released, then
the total mass must be decreased. If energy is
absorbed, then the total mass must be
increased. However, the change of mass is too
small to be measured.
• In nuclear reaction, the changes in energy relative to the masses
involved are much larger, the corresponding change in mass can
be measured.
Example:
• total mass of two protons and two neutrons is 2(1.0073 u +
1.0087 u) = 4.0320 u
• The mass of a helium-4 is 4.0016 u
• The mass of the nucleus is less than its components. This is true
for every nucleus, with the exception for hydrogen-1, which has
only one nucleon.
Nuclear fission and fusion
•
•
Nuclear fission is a nuclear reaction in which the nucleus of an
atom splits into smaller parts (lighter nuclei). Fission of heavy
elements is an exothermic reaction which can release large
amounts of energy both as electromagnetic radiation and as
kinetic energy of the fragments (heating the bulk material where
fission takes place).
Nuclear fusion is the process by which two or more atomic
nuclei join together, or "fuse", to form a single heavier nucleus.
This is usually accompanied by the release or absorption of large
quantities of energy. The fusion of two nuclei with lower masses
than iron (which, along with nickel, has the largest binding
energy per nucleon) generally releases energy while the fusion
of nuclei heavier than iron absorbs energy
Studying atomic nuclei
• The structure of the atomic nucleus and the nature of matter
have been investigated using particle accelerators.
• Particle accelerators use electric and magnetic fields to
increase the kinetic energies of charged particles, such as
electrons and protons, and project them at speeds near the
speed of light.
• Collisions between the high speed particles and atomic nuclei
may disrupt the nuclei and release new particles.
Review – dual nature of
light, quantum theory
example
• What is the amount of energy in one kilogram of mass?
E = mc2
E = (1 kg) x (3.00 x 108 m/s)2
= 9.00 x 1016 J
• Kilogram is very big unit of mass in the reference of massenergy conversion.
• Universal mass unit (u) is used:
1 u = 9.31 x 102 MeV
example
•
1.
2.
3.
4.
According to the chart, the energy equivalent of
the rest mass of a proton is approximately
9.4 x 102 MeV
When the unit is u (atomic mass unit),
3
1.9 x 10 MeV converts the mass into MeV instead of
9.0 x 1016 MeV Joules.
6.4 x 1018 MeV
2
1 u = 9.31 x 10 MeV
1.0073 u = 9.4 x 102 MeV
Example
•
1.
2.
3.
4.
The graph represents the relationship
between mass and its energy
equivalent. The slope of the graph
represents
the electrostatic constant
gravitational field strength
the speed of light squared
Planck's constant
E = mc2
4. The standard model of particle
physics - objectives
1. State the standard model of particle
physics
2. Describe the fundamental forces in
nature
3. Classify subatomic particles
Standard model of particle physics
..\..\RealPlayer Downloads\CERN- The
• The Standard Model of
Standard Model Of Particle Physics.flv
particle physics (formulated
in the 1970s) describes the
universe in terms of
Matter (fermions - 24) and
Force (bosons - 4).
• Unlike the force-carrying
particles, the matter
particles have associated
antimatter particles, such
as the antielectron (also
called positron) and
antiquarks. So there are
together 24 fermions.
The fundamental forces in nature
• There are four known forces. Two of these forces are only seen in
atomic nuclei or other subatomic particles. Aside from gravity, all
the macroscopically observable forces — such as friction & pressure
as well as electrical & magnetic interaction — are due to
electromagnetic force.
– Gravitational (not in standard model)
– Electromagnetic
– strong nuclear
– Weak nuclear
• ..\..\RealPlayer Downloads\The Weak and Strong Nuclear Forces (9
of 15).flv
• The weak nuclear force is another very short-range nuclear force
that causes transformation of protons to neutrons and vice-versa,
along with other radioactive (gives off photons and other particles)
phenomena.
• The Standard Model describe the force between two particles in
terms of the exchange of virtual force carrier particles between
them.
force
Relative
strength
range
Force
carrier
mass
charge
Strong
nuclear
1038
~10-15 m
gluon
0
0
ElectroMagnetic
Weak
nuclear
1036
~1/r2
photon
0
0
1025
10-18 m
W boson
W boson
Z boson
80.6 GeV
80.6 GeV
91.2 GeV
+e
-e
0
gravitational
1
~1/r2
graviton
0
0
GRAVITY
Gravitation is a force of attraction that acts between each and
every particle in the Universe. It is the weakest of the four
fundamental forces. It is always attractive, never repulsive. It pulls
matter together, causes you to have a weight, apples to fall from
trees, keeps the Moon in its orbit around the Earth, the planets
confined in their orbits around the Sun, and binds together galaxies
in clusters.
THE ELECTROMAGNETIC FORCE
• The electromagnetic force determines the
ways in which electrically charged
particles interact with each other and also
with magnetic fields. This force can be
attractive or repulsive.
• This force holds the atoms together.
• This force also governs the emission and
absorption of light and other forms of
electromagnetic radiation.
THE STRONG NUCLEAR FORCE
• The strong nuclear force binds together
the protons and neutrons that comprise
an atomic nucleus and prevents the
mutual repulsion between positively
charged protons from causing them to fly
apart.
• The strong nuclear force interaction is the
underlying source of the vast quantities of
energy that are liberated by the nuclear
reactions that power the stars.
THE WEAK NUCLEAR FORCE
• The weak nuclear force causes the
radioactive decay of certain particular
atomic nuclei. In particular, this force
governs the process called beta decay
whereby a neutron breaks up
spontaneously into a proton, and electron
and an antineutrino.
LONG-RANGE and SHORTRANGE FORCES
• The strong and weak nuclear interactions
are effective only over extremely short
distances. The range of strong force is
about 10-15 meters and that of the weak
force is 10-18 meters.
• In contrast, the electromagnetic and
gravitational interactions are long-range
forces, their strengths being inversely
proportional to the square of distance.
Force carriers
• According to modern quantum theories, the
various fundamental forces are conveyed
between real particles by means of virtual
particles. The force-carrying particles (which are
known as gauge bosons) for each of the forces
are as follows:
– electromagnetic force - photons;
– weak nuclear interaction - very massive 'W'
and 'Z' bosons;
– strong nuclear interaction - gluons.
– gravitation - graviton.
The fundamental forces
force
Relative Range of
strength force
Strong (nuclear)
1
electromagnetic
10-2
weak
10-13
gravitational
Force
carrier
mass
charge
~ 10-15m gluon
0
0
~ 1/r2
photon
0
0
W boson
W boson
Z boson
80.6 GeV
80.6 GeV
91.2 GeV
+e
-e
0
graviton
0
0
<
10-18m
10-38 ~ 1/r2
example
1. Which force is responsible for a neutron
decaying into a proton? Weak force
2. Which force bonds quarks together into
particles like protons and neutrons?
strong force
3. Which force governs the motion of an apple
falling from a tree?
Gravitational force
4. What are
you made
of? What
forces
hold you
together?
Sub-Atomic Particles
• Although the Proton, Neutron and Electron have
been considered the fundamental particles of an
atom, recent discoveries from experiments in
atomic accelerators have shown that there are
actually 12 fundamental particles (with 12
antiparticles). Protons and neutrons are no
longer considered fundamental particles in this
sub-atomic classification.
• ..\..\RealPlayer Downloads\CERN- The Standard
Model Of Particle Physics.flv
Matter
Hadrons (held
together by strong
force)
Baryons(3 quarks)
Protons and neutrons
Leptons
(no strong Force)
Mesons
(quark & anitquark)
The fundamental particles are classified into two
classes: quarks and leptons
Hadrons and lepton
• Particles can be classified according to the types
of interactions they have with other particles.
• A particle that interacts through the strong
nuclear force, as well as the electromagnetic,
weak and gravitational forces is called a hadron.
• A particle that interacts through the
electromagnetic, weak and gravitational forces,
but not the strong nuclear force, is called a
lepton.
Hadrons – baryons & mesons
• Hadrons group can be subdivided into baryons
and mesons.
– Baryons are made of three quarks, the
charges on a baryon can be 0, +1, or -1
– examples of baryons are neutrons, protons.
– The term "baryon" is derived from the Greek
βαρύς (barys), meaning "heavy.“
• Mesons are made a quark-antiquark pair,
mesons is a particle of intermediate mass.
• All hadrons are constructed of quarks.
A baryon is made up of 3
quarks, for example:
A proton consists of up, up,
down quarks
A neutron consists of up,
down, down quarks
When quarks combine to
form baryons, their charges
add algebraically to a total
of 0, +1, -1.
example
•
1.
2.
3.
4.
Baryons may have charges of
+1e and + 4/3 e
+2e and +3e
-1e and +1e
-2e and - e
example
•
1.
2.
3.
4.
Protons and neutrons are examples of
positrons
baryons
mesons
quarks
What are Leptons?
• A lepton has a mass much less than that of a
proton, the lepton classification of sub-atomic
particles consists of 6 fundamental particles:
– Electron
– Muon
– Tau
– Electron Neutrino
– Muon Neutrino
– Tau Neutrino
• The reference tables give the names, symbols
and charges of the six members of the lepton
family.
Electron, Muon and Tau Leptons
• The Electron remains a fundamental particle, as
if was in the Atomic Theory. It has an electrical
charge of (-1) and plays an active role in
chemical reactions.
• The Muon is primarily a result of a high-energy
collision in an atomic accelerator. The Muon is
similar to an Electron, only heavier.
• The Tau particle is similar to a Muon, only
heavier yet.
• Muon and Tau particles are unstable and exist in
nature for a very short time.
Neutrinos
• Neutrinos are small and have no electrical
charge. This makes them extremely difficult to
detect. They can possess a large amount of
energy and the very rare times they do collide
with another particle, that energy can be
released.
• There are 3 types of neutrinos:
– Electron Neutrino, which has no charge and
is extremely difficult to detect
– Muon Neutrino, which is created when some
atomic particles decay
– Tau Neutrino, which is heavier than the Muon
Neutrino.
Quarks
• Another group of sub-atomic particles are the
Quarks. Just like their name, they exhibit
unusual characteristics. There are 6
fundamental particles among the Quarks are:
• Up and Down Quarks
• Charm, Strange, Top and Bottom Quarks
• Other particles are made up of combination of
Quarks.
• The reference table gives the names, symbols,
and charges of the six quarks.
Up and Down Quarks
• The Up Quark has an electrical charge of
(+2/3). The Down Quark has an electrical
charge of (-1/3).
• The Proton is made up of two Up Quarks and
one Down Quark. The electrical charge of the
proton is then: (+2/3) + (+2/3) + (-1/3) = (+1).
• The Neutron is made up of one Up Quark and
two Down Quarks. The resulting electrical
charge of the Neutron is: (+2/3) + (-1/3) + (-1/3)
= (0).
Charm, Strange, Top and Bottom
Quarks
• The Charm Quark has the same electrical
charge as the Up Quark but is heavier.
The Top Quark is then heavier than the
Charm.
• The Strange Quark has the same
electrical charge as the Down Quark but
is heavier. The Bottom Quark is heavier
than the Strange.
Particles in
matter
hadrons
baryons
mesons
3 quarks
quark and
antiquark
6 types of
quarks
leptons
6 types
antiparticle
• An antiparticle is associated with each particle.
• An antiparticle is a particle having mass, lifetime,
and spin identical to the associated particle, but
with charge of opposite sign (if charged) and
magnetic moment reversed in sign. An
antiparticle is denoted by a bar over the symbol
of the particle.
• Example: p, stands for antiproton, which can be
described as a stable baryon carrying a unit
negative charge, but having the same mass as a
proton.
• A positron (+e) is a particle whose mass is
equal to the mass of the electron and whose
positive electric charge is equal in magnitude to
the negative charge of the electron.
• Positron is the antiparticle of electron (e).
• The antineutron (n) has the same mass as the
neutron and is also electrically neutral. However
the magnetic moment and spin of the
antineutron are in the same direction, whereas,
the magnetic moment and spin of the neutron
are in opposite directions.
• Antiparticle for a neutrino is identical to the
neutrino except for their direction of spin.
Fundamental
Fundamental
particles
particles
quarks
antiquarks
leptons
6
6
6
There are total of 24 basic particles
antileptons
6
antimatter
• Antimatter is material consisting of atoms
that are composed of antiprotons,
antineutrons, and positrons.
Examples
1.
The subatomic particles that make up both protons
and neutrons are known as
a. electrons
b. nuclides
c. positrons
d. Quarks
2.
A lithium atom consists of 3 protons, 4 neutrons, and 3
electrons. This atom contains a total of
a. 9 quarks and 7 leptons
b. 12 quarks and 6 leptons
c. 14 quarks and 3 leptons
d. 21 quarks and 3 leptons