Do Now (2/21/14): What does the word “quantized” mean? Where have we seen quantization in Physics? What is the structure of an atom?

Do Now (2/21/14):Do Now (2/21/14):

What does the word “quantized” mean?Where have we seen quantization in

Physics?What is the structure of an atom?

ObjectivesObjectives

Define photoelectric effect and evidence of particle properties of light.

Define work function.Calculate energy of a photon and an

electron.Determine Planck’s constant.

Particles and Waves Particles and Waves

Quantum TheoryQuantum Theory

Max Planck (1900) recognized electromagnetic radiation is quantized as E=hf.

1905, Einstein proposed photon theory of light. Supported by work in photoelectric effect.

Photoelectric EffectPhotoelectric Effect

E = KE + WEnergy of impinging light equals KE of

electron plus the work function.Intensity increases will increase current.Frequency changes affect KE.

2/28/12

NewtonNewton

Thought of light as particles

Maxwell’s Theory Maxwell’s Theory

Light is composed of crossed electric and magnetic fields which make up a wave.

Experiments show that when light shines on a metal surface, the surface emits electrons.

Planck’s WorkPlanck’s WorkIn 1900, Max Planck came up with a formula to

explain radiation from objects, but the formula only made sense if the energy of a vibrating molecule was quantized.

What are some other examples of “quantization”?

Planck’s ConstantPlanck’s Constant

Einstein’s TheoryEinstein’s TheoryBased on Planck's work,

Einstein proposed that light also delivers its energy in chunks

light consists of particles (quanta) called photons, each with an energy of Planck's constant times its frequency

PhotonPhoton

a light quantum that is massless, has energy and momentum, and travels at the speed of light

The Photoelectric Effect The Photoelectric Effect

the emission of electrons produced when electromagnetic radiation falls on certain materials

Threshold Frequency fThreshold Frequency f00

the minimum frequency of incident light which can cause photo electric emission

Energy of a photonEnergy of a photon

E=hfh=Planck’s constant

f=frequency

Electron VoltsElectron Volts

1 eV= 1.6x10-19 J

λ=wavelength

nmeVhc

E

1240

Example:Example:Calculate the wavelength and the energy of a photon of

light with frequency equal to 1.984 x 1014 Hz.• Calculating the wavelength, from :

c=fλ 3x108=λ (1.984 x 1014 )= 1.51 x 10-6 m

• Calculating the energy of the photon:

E = hf E = 6.628 x 10-34 x 1.984 x 1014

= 1.31 x 10-19 J

KE of photonKE of photon

hf0=min. energy to release electron

hc

- hc

=hf-hf=-E=KE0

0photon

Stopping Potential (Stopping Potential (Vo)Vo)

The negative potential at which the photo electric current becomes zero

Example: Example: The stopping potential of a certain photocell

is 4 V. What is the KE given to the electrons by the incident light?

KE=-W

KE=-qV0

KE=-(1.6x10-19)(4)=+6.4x10-19J

Work Function Work Function ϕϕ00

Minimum amount of energy which is necessary to start photo electric emission.

It is a property of material. Different materials have different values of work function.

Einstein’s TheoryEinstein’s Theory

hf = + ½ mv2

hf : energy of each photon

Source: http://www.westga.edu/~chem/courses/chem410/410_08/sld017.htm

Kinetic energy of emitted electron Kinetic energy of emitted electron vs. Light frequencyvs. Light frequency

Higher-frequency photons have more energy, so they make electrons come out faster; same intensity but a higher frequency increases the max KE of the emitted electrons.

If frequency is the same but intensity higher , more electrons come out (because there are more photons to hit them), but they won't come out faster, because each photon still has the same energy.

if the frequency is low enough, then none of the photons will have enough energy to knock an electron out. If you use really low-frequency light, you shouldn't get any electrons, no matter how high the intensity is. if you use a high frequency, you should still knock out some electrons even if the intensity is very low.

Source: http://online.cctt.org/physicslab/content/PhyAPB/lessonnotes/dualnature/photoelectric.asp

Source: http://sol.sci.uop.edu/~jfalward/particlesandwaves/phototube.jpg

Simple Photoelectric Experiment

Photoelectric EffectPhotoelectric Effect

Applications

ApplicationsApplications The Photoelectric effect has numerous applications, for

example night vision devices take advantage of the effect. Photons entering the device strike a plate which causes electrons to be emitted, these pass through a disk consisting of millions of channels, the current through these are amplified and directed towards a fluorescent screen which glows when electrons hit it. Image converters, image intensifiers, television camera tubes, and image storage tubes also take advantage of the point-by-point emission of the photocathode. In these devices an optical image incident on a semitransparent photocathode is used to transform the light image into an “electron image.” The electrons released by each element of the photoemitter are focused by an electron-optical device onto a fluorescent screen, reconverting it in the process again into an optical image

Applications: Night Vision Applications: Night Vision DeviceDevice

http://www.lancs.ac.uk/ug/jacksom2/

Photoelectric Effect ApplicationsPhotoelectric Effect Applications Photoelectric Detectors In one type of

photoelectric device, smoke can block a light beam. In this case, the reduction in light reaching a photocell sets off the alarm. In the most common type of photoelectric unit, however, light is scattered by smoke particles onto a photocell, initiating an alarm. In this type of detector there is a T-shaped chamber with a light-emitting diode (LED) that shoots a beam of light across the horizontal bar of the T. A photocell, positioned at the bottom of the vertical base of the T, generates a current when it is exposed to light. Under smoke-free conditions, the light beam crosses the top of the T in an uninterrupted straight line, not striking the photocell positioned at a right angle below the beam. When smoke is present, the light is scattered by smoke particles, and some of the light is directed down the vertical part of the T to strike the photocell. When sufficient light hits the cell, the current triggers the alarm.

Source: http://chemistry.about.com/cs/howthingswork/a/aa071401a.htm

Photoelectric Smoke DetectorPhotoelectric Smoke Detector

Source: http://www.bassburglaralarms.com/images_products/d350rpl_addressable_duct_smoke_detector_b10685.jpg

ApplicationsApplications

Solar panels are nothing more than a series of metallic plates that face the Sun and exploit the photoelectric effect. The light from the Sun will liberate electrons, which can be used to heat your home, run your lights, or, in sufficient enough quantities, power everything in your home.

Source: www.futureenergy.org/ picsolarpannelsmatt.jpg

Work CitedWork Cited

Amar, Francois G. The Photoelectric Effect. 25 Sep 2003. Section of Chemistry 121 for fall 03. 11 May 2006 <http://chemistry.umeche.maine.edu/~amar/fall2003/photoelectric.html>

Blawn, Jeramy R. and Colwell, Catharine H. Physics Lab: Photoelectric Effect. 10 Jun 2003. Mainland High School: Online Physics Labs. 11 May 20006 <http://online.cctt.org/physicslab/content/PhyAPB/lessonnotes/dualnature/photoelectric.asp>

Helmenstine, Anne Marie. Photoelectric & Ionization Smoke Detector. 25 Feb 2006. About.com. 11 May 2006 <http://chemistry.about.com/cs/howthingswork/a/aa071401a.htm>

Einstein, Albert. “Concerning an Heuristic Point of View Toward the Emission and Transformation of Light.” American Journal Of Physics 5 May 1965: 137.

Nave, Rod. HyperPhysics. 19 Aug. 2000. Georgia State University. 06 May 2006 <http://hyperphysics.phy-astr.gsu.edu/hbase/hframe.html> .

Thornton T., Stephen, and Rex, Andrew. Modern Physics for Scientists and Engineers. Canada : Thomson Brooks/Core, 2006

Photoelectric Effect. 24 Apr. 2006. Wikipedia Free Encyclopedia. 05 May 2006. <http://en.wikipedia.org/wiki/Photoelectric_effect>.

Do Now (2/25/14):Do Now (2/25/14):

In your own words, describe the photoelectric effect. Use the words “work function,” “threshold frequency,” “electron,” and “photon,” at least once in your paragraph.

Agenda:Agenda:

Finish competitionComplete Quantum lectureComplete Chapter 27 Multiple Choice

Questions Introduce tomorrow’s lab

White Board Competition!White Board Competition!

Work in groups For each correct question, make a tally in

the upper right hand corner of your board. BE HONEST!!!

The teams with the most points at the end will receive extra credit!

#1#1According to Einstein, the energy of a

photon depends on the _________ of the electromagnetic radiation.

A.momentum

B. speed

C. frequency

D. intensity

#2#2The work function of iron is 4.7 eV.

What is the threshold wavelength of iron?

A.2.60 nm

B. 260 nm

C. 470 nm

D. 2600 nm

#3#3The stopping potential, V0, that prevents

electrons from flowing across a certain photocell is 6.0 V. What is the kinetic energy in J given to the electrons by the incident light?

A.9.6 x 10-19 J

B.1.60 x 10-19 J

C.6.9 x 10-19 J

D. 6.4 x 10-19 J

#4#4When light is directed on a metal surface, the

kinetic energies of the electrons

A.vary with the intensity of light

B.vary with the speed of light

C.vary with the frequency of the light

D.are random

#5#5The threshold frequency for photoelectric

emission in copper is 1.1 x 1015 Hz. What is the maximum kinetic energy in eV of the photoelectrons when light of frequency 1.5 x 1015 Hz is directed on a copper surface?

A.2.65 eV

B. 2.12 eV

C. 1.66 eV

D. 1.03 eV

#6#6What will likely happen if a light whose

frequency is below the threshold frequency hits a clean metal surface?

A. no electron will be ejected from the metal

B. fewer electrons will be ejected from the metal

C. more electrons will be ejected from the metal

D. ejected electrons will have higher kinetic energy

#7#7What is the work function of a

metal whose threshold frequency is 3.5 x 1015 Hz?

A.2.32 x 10-18 J

B. 3.11 x 10-18 J

C. 3.65 x 10-18 J

D. 4.01 x 10-18 J

#8#8What is the maximum wavelength of

light that will cause photoelectrons to be emitted from sodium if the work function of sodium is 2.3 eV?

A.1.75 x 10-7 m

B. 3.44 x 10-7 m

C. 5.40 x 10-7 m

D. 5.88 x 10-7 m

#9#9What will the maximum kinetic energy

of the photoelectrons be if 200-nm light falls on a sodium surface (work function is 2.3 eV)?

A.2.96 x 10-19 J

B. 4.73 x 10-19 J

C. 5. 21 x 10-19 J

D. 6.26 x 10-19 J

#10#10When 230-nm light falls on a metal, the current

through the photoelectric circuit is brought to zero at a reverse voltage of 1.64 V. What is the work function of the metal?

A.4. 39 x 10-19 J

B. 5.38 x 10-19 J

C. 6.01 x 10-19 J

D. 7.11 x 10-19 J

#11#11The current in a photoelectric effect experiment

decreases to zero when the retarding voltage is raised to 1.25 V. What is the maximum speed of the electrons?

A.6.63 x 105 m/s

B. 5.53 x 105 m/s

C. 4.78 x 105 m/s

D. 4.19 x 105 m/s

#12#12What is the maximum speed of an electron ejected

from a sodium surface whose work function is 2.28 eV when illuminated by light of wavelength 450 nm?

A.3.25 x 105 m/s

B. 4.10 x 105 m/s

C. 4.85 x 105 m/s

D. 5.25 x 105 m/s

#13#13Light is incident on the surface of metallic sodium,

whose work function is 2.3 eV. The maximum speed of the photoelectrons emitted by the surface is 1.2 x 106 m/s. What is the wavelength of the light?

A.1.95 x 10-7 m

B. 2.42 x 10-7 m

C. 2.86 x 10-7 m

D. 3.01 x 10-7 m

#14#14Ultraviolet radiation (wavelength 250 nm) falls on

a metal target and electrons are liberated. If the maximum kinetic energy of these electrons is 1.00 x 10-19 J, what is the lowest frequency of electromagnetic radiation that will initiate a photocurrent on this target?

A.1.05 x 1015 Hz

B. 1.35 x 1015 Hz

C. 1.65 x 1015 Hz

D. 1.78 x 1015 Hz

#15#15Photons of wavelength 220 nm on a metal target

and liberate electrons with kinetic energies ranging from 0 to 61 x 10-20 J. Determine the threshold wavelength of the metal.

A.1.68 x 10-7 m

B. 1.95 x 10-7 m

C. 2.06 x 10-7 m

D. 6.77 x 10-7 m

#1#1http://lrt.ednet.ns.ca/PD/ict_projects/photoelectric

/index.htm

Photoelectric EffectPhotoelectric Effect When light shines on a surface (metal), electrons are

emitted from the surface. E = KEe + W0

Energy of impinging light equals KE of electron plus the work function.

Light Intensity increases will increase current (# of electrons).

Frequency changes affect KEe.

Contributes to the theory of light as a particle. The photons absorbed are “packets” of light energy.

Work FunctionWork Function

The minimum energy required is called the work function, W0

If hf < W0 then no electrons are emitted

The lower the energy required to expel the electron, the faster the electron will be moving away from the surface.

This makes it more likely be able to escape from the material entirely.

practicepractice What is the work function when

monochromatic light of frequency 4.5x1015Hz releases the least tightly held electrons from a metal with a maximum KE of 13.10eV?

Do Now (2/25/14):Do Now (2/25/14):

A sodium surface is illuminated with light of wavelength 3 x 10-7 m. The work function for sodium is 2.46 eV. Find (a) the kinetic energy of the ejected photoelectron and (b) the cutoff wavelength for sodium.

QUANTUM PHYSICS: DAY 2QUANTUM PHYSICS: DAY 2

Blackbody RadiationBlackbody RadiationAn object an any temperature is known to

emit thermal radiationStefan’s Law:

Star TemperaturesStar TemperaturesStars approximate blackbody radiators and their visible

color depends upon the temperature of the radiator.

The curves show blue, white, and red stars. The white

star is adjusted to 5270K so that the peak of its

blackbody curve is at the peak wavelength of the sun,

550 nm.

Wien’s displacement law..From the wavelength at the peak, the

temperature can be deduced from the Wien displacement law.

Planck's HypothesisPlanck's HypothesisIn 1900 Max Planck proposed a formula for the

intensity curve which did fit the experimental data quite well. He set out to find a model that would produce his formula.

Instead of allowing energy to be continuously distributed among all frequencies, Planck's model required that the energy in the atomic vibrations of frequency f was some integer times a small, minimum, discrete energy, Emin = hf, where h is a constant, now known as Planck's constant,

h = 6.626176 x 10-34 J s

Planck’s HypothesisPlanck’s HypothesisPlanck's proposal requires that all the energy in

the atomic vibrations with frequency f can be written as E = n h f, where n = 1, 2, 3, . . . No other values of the energy were allowed. The atomic oscillators could not have energy of (2.73) hf or (5/8) hf.

This idea that something -- the energy in this case -- can have only certain discrete values is called quantization. We say that the energy is quantized. This is referred to as Planck's quantum hypothesis.

Planck’s HypothesisPlanck’s HypothesisPlanck did not realize how radical and far-

reaching his proposals were. He viewed his strange assumptions as mathematical constructions to provide a formula that fit the experimental data.

It was not until later, when Einstein used very similar ideas to explain the Photoelectric Effect in 1905, that it was realized that these assumptions described "real Physics" and were much more than mathematical constructions to provide the right formula.

X-RaysX-Rays

In 1895, Wilhelm Roentgen found a mysterious radiation in his lab, which he dubbed “x-rays.”

They are produced when high speed electrons are suddenly deccelerated

Any accelerating voltage applied must be higher than a certain threshold voltage

BremsstrahlungBremsstrahlungElectrons emit radiation

when they undergo a

deceleration in the target The continuous

radiation is called

Bremsstrahlung

(Gernan for

“braking

radiation”).

X-RaysX-RaysElectron energy:

hc

hfVe max

X-RaysX-Rays

In 1912, Max von Laue used a crystal lattice to diffract X-Rays.

This method become popular for analyzing matter

Bragg’s LawBragg’s LawWhen x-rays are scattered from a crystal lattice,

peaks of scattered intensity are observed which correspond to the following conditions:– The angle of incidence = angle of scattering.– The path length difference is equal to an integer

number of wavelengths.

md sin2

Bragg’s LawBragg’s Law

The condition for maximum intensity contained in Bragg's law above allow us to calculate details about the crystal structure, or if the crystal structure is known, to determine the wavelength of the x-rays incident upon the crystal.

The Compton Effect The Compton Effect

Compton deflected an x-ray of wavelength λ0 toward a block of graphite.

The reflected rays had a longer wavelength than the incident rays.

This change is called the Compton Shift.

The Compton EffectThe Compton Effect

Could only be explained using particles (momentum)

cos10 cm

h

e

Example:Example:

X-rays of wavelength 0.200000 nm are scattered from a block of material. The scattered X-rays are observed at an angle of 45° to the incident beam. Calculate the wavelength of the x-rays scattered at this angle.

λ=0.200710 nm

Wave Particle dualityWave Particle duality

Light exists as both photons and as electromagnetic waves.

We must accept both models to fully describe it.

The Wave Properties of ParticlesThe Wave Properties of Particles

In 1932, Louis de Broglie postulated that because photons have wave properties, all matter could have wave properties.

The de Broglie Wavelength:The de Broglie Wavelength:The wavelength of a particle, given by

where h is Planck's constant and p is the momentum.

In the nonrelativistic limit, this can be written

where m is the particle mass and v is the velocity.

p

h

mv

h

Momentum and Energy of a Momentum and Energy of a photon:photon:

No mass? How do we calculate?

Davisson-GermerDavisson-Germer

Measured the wavelength of electrons accidentally proved de Broglie’s hypothesisLow energy electrons were shot at a nickel

target, which became oxidized accidentally. This made a diffraction grating for the electron matter waves.

Example:Example:Calculate the de Broglie wavelength for an

electron moving at 10 7 m/s.

Example.Example.

Calculate the de Broglie wavelength for a 50 g rock through with a speed of 40 m/s.

Schrodinger’s CatSchrodinger’s CatSchrödinger's cat is a thought

experiment (paradox) devised by Austrian physicist Erwin Schrödinger in 1935 that illustrates the principle of quantum theory of superposition.

Schrödinger's cat demonstrates the apparent conflict between what quantum theory tells us is true about the nature and behavior of matter on the microscopic level and what we observe to be true about the nature and behavior of matter on the macroscopic level -- everything visible to the unaided human eye.

Schrodinger’s Cat: (theoretical) experimentSchrodinger’s Cat: (theoretical) experimentWe place a living cat into a steel chamber, along

with a device containing a vial of hydrocyanic acid. There is, in the chamber, a very small amount of hydrocyanic acid, a radioactive substance. If a single atom of the substance decays during the test period, a relay mechanism will trip a hammer, which will, in turn, break the vial and kill the cat.

Schrodinger’s Cat ExperimentSchrodinger’s Cat ExperimentThe observer cannot know whether

or not an atom of the substance has decayed, and consequently, whether the vial has been broken, the hydrocyanic acid released, and the cat killed.

Since we cannot know, according to quantum law, the cat is both dead and alive, in what is called a superposition of states.

Thought ExperimentThought ExperimentIt is only when we break open

the box and learn the condition of the cat that the superposition is lost, and the cat becomes one or the other (dead or alive). This is sometimes called quantum indeterminacy or the observer's paradox: there is no single outcome unless it is observed.

Schodinger’s CatSchodinger’s CatSuperposition occurs at the

subatomic level, because there are observable effects of interference, in which a single particle is demonstrated to be in multiple locations simultaneously. What that fact implies about the nature of reality on the observable level (cats, for example, as opposed to electrons) is one of the stickiest areas of quantum physics.

Schrödinger himself is rumored to have said, later in life, that he wished he had never met that cat.

The Wave FunctionThe Wave Function

The Uncertainty PrincipleThe Uncertainty PrinciplePosition and momentum of a particle cannot be

simultaneously measured with arbitrarily high precision.

There is a minimum for the product of the uncertainties of these two measurements, as well as for the product of the uncertainties of the energy and time.

Uncertainty PrincipleUncertainty Principle

Not a statement about the inaccuracy of measurement instruments, nor a reflection on the quality of experimental methods

Arises from the wave properties inherent in the quantum mechanical description of nature.

Even with perfect instruments and technique, the uncertainty is inherent in the nature of things.

The Heisenberg Uncertainty The Heisenberg Uncertainty Principle:Principle:

(h bar)

Example:Example:

The speed of an electron is measured to be 5 x 103 m/s to an accuracy of 0.00300%. Find the uncertainty in determining the position of the electron.

Photoelectric CompetitionPhotoelectric Competition

Practice:Practice:

Complete the multiple choice problems in Chapter 27

Do Now (2/26/14) (7 minutes):Do Now (2/26/14) (7 minutes):

1. What is the de Broglie wavelength of a 0.050 gram projectile fired at 180m/s?

2. What kind of wave properties could we see from the wavelength in the above question?

3. In your own words, describe Schrodinger’s cat and what it represents.

4. Which equation(s) of Einstein’s have you seen before?

Pair Production and AnnihilationPair Production and AnnihilationPair production:

Pair annihilation:

Pair ProductionPair Production

The creation of an elementary particle and its antiparticle, usually when a photon interacts with a nucleus or another boson.

For example, an electron and its antiparticle, the positron, may be created.

Pair ProductionPair ProductionThe minimum energy that a photon must have

to produce a single electron-positron pair can be found using conservation of energy by equating the photon energy to the total rest energy of the pair

2min 2 cmhf e

Rest mass

energy

Pair annihilation Pair annihilation Occurs when an electron (e−) and a positron (e+)

collide. The result is the annihilation of the electron and positron, and the creation of gamma ray photons or, at higher energies, other particles:

e− + e+ → γ + γIt must satisfy a number of laws, including: Conservation of electric charge. Conservation of linear momentum and total energy. Conservation of angular momentum.

Electrons and positrons may also interact with each other without annihilating.

AgendaAgenda

Finish photoelectric competition Photoelectric Notes SheetUnits SheetConceptual QuestionMultiple Choice (if time)

Photoelectric Notes SheetPhotoelectric Notes SheetFill in the blanks on the note sheet; you may use

your peers and the book to help youTen minutes in, pink copies of the answer sheet

will be passed around. Check your work.Complete one problem from each section.When you finish, raise your hand so you may

receive a stampComplete any additional problems for extra

creditWe will discuss any questions afterwards.

Units SheetUnits Sheet

Complete one problem from each section.When you finish, raise your hand so you

may receive a stampComplete any additional problems for extra

credit

Conceptual QuestionsConceptual Questions

Work with your group to complete the conceptual questions.

Use a different color writing utensil for each group member

Do Now (2/27/14): (6 Min)Do Now (2/27/14): (6 Min)

Our next topic will be atomic physics. In that topic, we will see that electrons in atoms can be found in higher states of energy called excited states for short periods of time. If the uncertainty of the average time that an electron exists in one of these states is 1.00 x10-8 s, what is the minimum uncertainty in energy of the excited state?

Agenda:Agenda:

Complete Lecture Notes sheetWHEN FINISHED, continue working on

Units Practice SheetCheck answers for lecture notesComplete photoelectric mini lab

Do Now (2/28/14): (8 min)Do Now (2/28/14): (8 min)Find the maximum kinetic energy of

photoelectrons from a certain material if the work function is 2.3 eV and the frequency of radiation is 3 x 1015 Hz.

hfKE

Agenda:Agenda:

Quantum “test.”Conceptual questions

Quantum ChallengeQuantum Challenge

Work with your group using only your AP formula sheet and your calculators. Check your work with Ms. Timson when complete

The first group to get 100% gets bonus points

Do Now (3/4/14):Do Now (3/4/14):

In one sentence only, describe the following:– The Photoelectric Effect– The Compton Effect– The de Broglie Wavelength

What was the most productive thing you did over the snow weekend?

Agenda:Agenda:

Breifly review Quantum ChallengeGroup work – conceptual questionsAP free response practice

Conceptual QuestionsConceptual Questions

Work with your group to complete the conceptual questions.

Use a different color writing utensil for each group member

#13 – 18 are bonus, as well as #10 on the back (the last question)

Do Now (3/5/14): (on your Do Do Now (3/5/14): (on your Do Now sheet)Now sheet)

Complete parts a, b, & c from the AP free response problem you received yesterday (pink sheet)

You may complete d for extra credit

Review:Review:

Summary

Compton EffectCompton Effect

Short wavelength light (x-rays) scattered from materials had a lower frequency than the incident light.

Wave nature of light would not have shown this shift in wavelength. Explained only through particle explanations.

Wave Particle DualityWave Particle Duality

Apparently conflicting observations of wave nature and particle nature of light.

Principle of Complementarity (Niels Bohr)

E=hf is a nice bridge since it incorporates both particle and wave properties.

Wave Nature of MatterWave Nature of Matter

Louis DeBroglie

= h/(mv)Electrons vs. macroscopic matter

practicepractice What is the de Broglie wavelength of

a .050gram projectile fired at 180m/s?

Photons and MatterPhotons and Matter4 possible interactions of photon with matter:

– Scattering (Compton effect) with lower frequency but same speed (c).

– Photoelectric effect– Excitation of electron (if energy too small to

ionize)– Pair production-photon creates matter through

production of an electron and a positron

Do Now (3/3/14):Do Now (3/3/14):

Atomic StructureAtomic Structure

J.J. ThomsonErnest RutherfordNiels BohrEnergy level diagramsE = hf and c=fLowest n has lowest energy. (Most

negative)

Big IdeasBig Ideas Millikan Planck Rutherford DeBroglie Bohr Compton Atomic Spectra Photo-electric Effect Wave particle duality


J.J. Thomson

Millikan

Ernest Rutherford

Cathode Ray and the ElectronCathode Ray and the Electron

F=evB

Accurately determined the charge carried by an electron using his oil-drop experiment (1.602x10-19 coulomb)

Proved that this quantity is a constant Experimentally verified Einstein’s photoelectric

equation and made the first direct photoelectric determination of Planck’s constant

Explored the region of the spectrum between ultraviolet and X-radiation, extending the ultraviolet spectrum far beyond the known limit

Two parallel metal plates acquire charge when electric current is applied.

Atomizer sprays mist of oil droplets, which then fall slowly through a small hole.

Space between plates ionized by radiation and electrons attach themselves to oil droplets, giving them a negative charge

Ernest RutherfordErnest Rutherford

Rutherford HistoryRutherford History

Ernest Rutherford, 1st Baron Rutherford of Nelson, OM, FRS (30 August 1871 – 19 October 1937) was a New Zealand chemist who became known as the father of nuclear physics. He discovered that atoms have a small charged nucleus, and thereby pioneered the Rutherford model (or planetary model, which later evolved into the Bohr model or orbital model) of the atom, through his discovery of Rutherford scattering with his gold foil experiment. He was awarded the Nobel Prize in Chemistry in 1908.

The Experiment The Experiment

Rutherford ScatteringRutherford Scattering

This experiment showed that the positive matter in atoms was concentrated in an incredibly small volume and gave birth to the idea of the nuclear atom. In so doing, it represented one of the great turning points in our understanding of nature.

It also put a rest to the Thompson model of the atom because of the angle’s at which the particles were scattered away from the nucleus of the atoms was greater than the Thompson model said it could be.

Quantum theory – Max PlanckQuantum theory – Max Planck

In 1900 Planck postulated that energy is radiated in small, discrete units, which he called quanta.

he discovered a universal constant of nature, Planck's constant. Planck's law states that the energy of each quantum is equal to the frequency of the radiation multiplied by the universal constant.

E=hf

Planck’s constantPlanck’s constant

E=hfE=nhfE= energyn=integer (1,2,3…)h=constant= 6.626 *10-34 J*sf= frequency

practicepractice According to Plank’s quantum hypothesis,

which of the following could be the energy of molecular vibrations in a radiating object with a wavelength of λ?

a. 4λhcb. hc/2λc. 4hc/λd. 2λc/he. λhc/2


Niels BohrBohr model of the atomEnergy level diagrams

Bohr and Quantum Bohr and Quantum HypothesisHypothesis

Discharge spectrahf=Eu – Ei where Eu is energy of the upper

state.Orbit closest to the nucleus has lowest

energy (most negative). An electron at infinite distance has energy of 0 eV.

Energy Level DiagramsEnergy Level Diagrams

Minimum energy to remove an electron is binding energy or ionization energy.

13.6eV – energy required to remove an electron from the lowest state E1= -13.6eV up to E=0.

Lyman series, Balmer series, Paschen series for hydrogen atoms. – pg 848.

The diagram above shows the lowest four discrete energy levels of an atom. An electron in the n = 4 state makes a transition to the n = 2 state, emitting a photon of wavelength 121.9 nm.

(a) Calculate the energy level of the n = 4 state.


(b) Calculate the momentum of the photon.


The photon is then incident on a silver surface in a photoelectric experiment, and the surface emits an electron with maximum possible kinetic energy. The work function of silver is 4.7 eV.

(c) Calculate the kinetic energy, in eV, of the emitted electron.


(d) Determine the stopping potential for the emitted electron.

Documents

Do Now (2/21/14): What does the word “quantized” mean? Where have we seen quantization in Physics? What is the structure of an atom?