objectives
description
Transcript of objectives
![Page 1: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/1.jpg)
5/4 do now – on a new sheet
• 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.
v
n
![Page 2: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/2.jpg)
Modern Physics
1. Wave-Particle Duality of Energy and Matter
2. Models of Atoms
3. The Nucleus
4. The Standard Model of Particle Physics
![Page 3: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/3.jpg)
1. Wave-Particle Duality of Energy and Matterobjectives
• 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
![Page 4: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/4.jpg)
Light as a wave• Light is an electromagnetic wave produced by an oscillating
_______________________. The vibrating charges produce alternating _________________________________which are 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 _________________________________________________
2. Light exhibit wave behavior such as _________________________________________________
• However, the wave model of light can not explain interactions of light with matter
electric charges electric and magnetic fields
amplitude, wavelength, frequency, and velocity.
diffraction, interference, and the Doppler effect.
![Page 5: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/5.jpg)
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 plates, a current flow is measured. A current is simply a flow of electrons in a metal, such as a wire. Thus, the beam of light must be liberating electrons from one metal plate, which are attracted to the other plate by electrostatic forces. This results in a current flow.
An unusual phenomenon was discovered in the early 1900's. Photoelectric_EffectIf a beam of light is pointed at the negative end of a pair of charged plates, a current flow is measured which means the beam of light must be liberating 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
Waves have a particle nature
![Page 6: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/6.jpg)
Einstein explains photoelectric effect• ..\..\RealPlayer Downloads\Photoelectric Effect and Photoelectr
ic 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
![Page 7: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/7.jpg)
• 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
f
E
λ
Direct relationship Slope = h
Inverse relationship
Energy: E = h∙f
![Page 8: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/8.jpg)
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.
![Page 9: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/9.jpg)
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
![Page 10: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/10.jpg)
• In conclusion, light has both wave and particle nature.• Wave nature:
– Exhibit wave characteristics: _______________________________________________________
– Exhibit wave behavior:– _______________________________________________
• Particle nature:– ________________________________________
– _________________________________– _________________________________
wavelength, frequency, crests, troughs, amplitude …
interference, diffract, Doppler effect, refract, reflect …
Photoelectric effect
Interact with electron – has momentumReflect like a particle
![Page 11: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/11.jpg)
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
![Page 12: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/12.jpg)
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
![Page 13: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/13.jpg)
In summary
• Waves has particle nature, it has momentum just like a particle:
• Particle has wave nature, it has a wavelength just like a wave:
p = h / λ
λ = h / p
![Page 14: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/14.jpg)
Example1. 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
![Page 15: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/15.jpg)
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
![Page 16: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/16.jpg)
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
c
b
d
Example
![Page 17: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/17.jpg)
Class work
• Worksheet 6.1.1 #1, 3, 5-9, 11
• Review questions #1-11
![Page 18: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/18.jpg)
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
![Page 19: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/19.jpg)
2. Models of an Atom objectives1. 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 model5. Explain why only certain energy levels
are permitted in atoms.
Homework: castle learning
![Page 20: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/20.jpg)
• 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.
![Page 21: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/21.jpg)
• 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.
Thompson’s model
![Page 22: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/22.jpg)
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.
![Page 23: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/23.jpg)
• In Rutherford’s model of the atom, electrons orbit the nucleus in a manner similar to planets orbiting the sun.
![Page 24: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/24.jpg)
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.
![Page 25: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/25.jpg)
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.
![Page 26: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/26.jpg)
• 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.
![Page 27: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/27.jpg)
• 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.
![Page 28: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/28.jpg)
• 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
![Page 29: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/29.jpg)
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.
![Page 30: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/30.jpg)
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.
![Page 31: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/31.jpg)
Energy level diagram• 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.Ground state
ionization
![Page 32: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/32.jpg)
Ephoton = Einitial - Efinal
• This formula can be used to determine the energy of the photon emitted (+) or absorbed(-).
Ephoton = hf
where h = 6.63 x 10-34 Js
• This formula can be used to determine the energy of a photon if you know the frequency of it. Planck's constant, h, can be used in terms of Joule(s) or eV(s). (note: the Regents reference table only gives it in terms of Js)
![Page 33: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/33.jpg)
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.
![Page 34: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/34.jpg)
..\..\RealPlayer Downloads\Quantum Mechanics- The Structure Of Atoms.flv
![Page 35: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/35.jpg)
Limitations of Bohr’s model
• It can not predict or explain the electron orbits of elements having many electrons
• ..\..\RealPlayer Downloads\Quantum Mechanics.flv
![Page 36: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/36.jpg)
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.
![Page 37: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/37.jpg)
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
![Page 38: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/38.jpg)
• Which diagram shows a possible path of an alpha particle as it passes very near the nucleus of a gold atom?
A. 1
B. 2
C. 3
D. 4
example
![Page 39: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/39.jpg)
• In Rutherford's model of the atom, the positive charge
1. is distributed throughout the atom's volume
2. revolves about the nucleus in specific orbits
3. is concentrated at the center of the atom
4. occupies most of the space of the atom
example
![Page 40: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/40.jpg)
Class work
• Worksheet 6.1.1 #1, 3, 5-9, 11
• Review questions #1-11
• Review questions #12-19
![Page 41: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/41.jpg)
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
![Page 42: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/42.jpg)
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.
![Page 43: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/43.jpg)
• According to Bohr’s model, electrons in atoms can be found in only certain discrete energy states.
Atomic spectra
![Page 44: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/44.jpg)
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.
![Page 45: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/45.jpg)
• 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
![Page 46: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/46.jpg)
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.
![Page 47: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/47.jpg)
• 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
![Page 48: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/48.jpg)
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.
![Page 49: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/49.jpg)
• 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.
Absorption spectra
![Page 50: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/50.jpg)
Example1. 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
![Page 51: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/51.jpg)
2. 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?
A. 1
B. 2
C. 3
D. 4
example
![Page 52: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/52.jpg)
![Page 53: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/53.jpg)
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.
![Page 54: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/54.jpg)
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.
![Page 55: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/55.jpg)
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.
![Page 56: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/56.jpg)
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.
![Page 57: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/57.jpg)
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
![Page 58: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/58.jpg)
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.
![Page 59: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/59.jpg)
• 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.
![Page 60: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/60.jpg)
• 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
Nuclear fission and fusion
![Page 61: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/61.jpg)
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
![Page 62: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/62.jpg)
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 mass-energy conversion.
• Universal mass unit (u) is used:
1 u = 9.31 x 102 MeV
![Page 63: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/63.jpg)
• According to the chart, the energy equivalent of the rest mass of a proton is approximately
1. 9.4 x 102 MeV
2. 1.9 x 103 MeV
3. 9.0 x 1016 MeV
4. 6.4 x 1018 MeV 1 u = 9.31 x 102 MeV
1.0073 u = 9.4 x 102 MeV
When the unit is u (atomic mass unit), converts the mass into MeV instead of Joules.
example
![Page 64: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/64.jpg)
• The graph represents the relationship between mass and its energy equivalent. The slope of the graph represents
1. the electrostatic constant
2. gravitational field strength
3. the speed of light squared
4. Planck's constantE = mc2
Example
![Page 65: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/65.jpg)
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
![Page 66: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/66.jpg)
• The Standard Model of 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.
Standard model of particle physics..\..\RealPlayer Downloads\CERN- The Standard Model Of Particle Physics.flv
![Page 67: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/67.jpg)
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.
![Page 68: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/68.jpg)
force Relative strength
range Force carrier
mass charge
Strongnuclear
1038 ~10-15 m gluon 0 0
Electro-
Magnetic
1036 ~1/r2 photon 0 0
Weak nuclear
1025 10-18 m W boson
W boson
Z boson
80.6 GeV
80.6 GeV
91.2 GeV
+e-e0
gravitational 1 ~1/r2 graviton 0 0
• The Standard Model describe the force between two particles in terms of the exchange of virtual force carrier particles between them.
![Page 69: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/69.jpg)
GRAVITYGravitation 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.
![Page 70: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/70.jpg)
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.
![Page 71: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/71.jpg)
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.
![Page 72: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/72.jpg)
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.
![Page 73: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/73.jpg)
LONG-RANGE and SHORT-RANGE 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.
![Page 74: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/74.jpg)
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.
![Page 75: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/75.jpg)
The fundamental forces
force Relative strength
Range of force
Force carrier mass charge
Strong (nuclear) 1 ~ 10-15m gluon 0 0
electromagnetic 10-2 ~ 1/r2 photon 0 0
weak 10-13 < 10-18m W bosonW bosonZ boson
80.6 GeV 80.6 GeV 91.2 GeV
+e-e0
gravitational 10-38 ~ 1/r2 graviton 0 0
![Page 76: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/76.jpg)
example1. Which force is responsible for a neutron
decaying into a proton?
2. Which force bonds quarks together into particles like protons and neutrons?
3. Which force governs the motion of an apple falling from a tree?
Weak force
strong force
Gravitational force
![Page 77: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/77.jpg)
4. What are you made of? What forces hold you together?
![Page 78: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/78.jpg)
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
![Page 79: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/79.jpg)
Matter
Hadrons (held together by strong
force)
Leptons (no strong Force)
Baryons(3 quarks)Protons and neutrons
Mesons(quark & anitquark)
The fundamental particles are classified into two classes: quarks and leptons
![Page 80: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/80.jpg)
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.
![Page 81: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/81.jpg)
• 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.
Hadrons – baryons & mesons
![Page 82: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/82.jpg)
• 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.
![Page 83: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/83.jpg)
example
• Baryons may have charges of
1. +1e and + 4/3 e
2. +2e and +3e
3. -1e and +1e
4. -2e and - e
![Page 84: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/84.jpg)
example
• Protons and neutrons are examples of
1. positrons
2. baryons
3. mesons
4. quarks
![Page 85: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/85.jpg)
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.
![Page 86: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/86.jpg)
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.
![Page 87: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/87.jpg)
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.
![Page 88: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/88.jpg)
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.
![Page 89: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/89.jpg)
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).
![Page 90: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/90.jpg)
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.
![Page 91: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/91.jpg)
Particles inmatter
hadrons leptons
baryons mesons
3 quarksquark and antiquark
6 types
6 types of quarks
![Page 92: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/92.jpg)
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.
![Page 93: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/93.jpg)
• 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.
![Page 94: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/94.jpg)
Fundamentalparticles
Fundamentalparticles
6 6 6 6
quarks antiquarks leptons antileptons
There are total of 24 basic particles
![Page 95: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/95.jpg)
antimatter
• Antimatter is material consisting of atoms that are composed of antiprotons, antineutrons, and positrons.
![Page 96: objectives](https://reader035.fdocuments.us/reader035/viewer/2022062517/56813ad0550346895da2f6e8/html5/thumbnails/96.jpg)
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