Rob’s favorite story!!!

• 6.1 Electromagnetic Radiation

• 6.2 Quantization: Planck, Einstein, Energy, and Photons.

• 6.3 Atomic Line Spectra and Neils bohr

Military laser information

• Military US Navy info on lasers

• An index of Technologies that profit from the unique properties of Lasers LASER SAFETY

• Some representative Laser types

• The Argon Ion laser

• I. What is a laser? a) A Brief History of the Laser II. How does a laser work? a) Atomic structure, radiation and emission b) Population inversion c) Argon as an excitation medium

Argon as an excitation medium

• The neutral argon atom is pumped to the 4p energy level -the origin of the lasing transition- by two collisions with electrons. The first ionizes the atom and the second excites it from the ground state E1 either directly to the 4p level (E3) or to E4, from which it cascades almost immediately to 4p. The 4p ions eventually decay to 4s (E2), either spontaneously or when stimulated to do so by a photon of appropriate energy.

• The wavelength of the photon depends on the specific energy levels involved, but will be between 400 and 600 nm. The ion decays spontaneously from 4s to the ground state emitting an ultraviolet photon, about 74 nm.

Population inversion of energy

http://itl.chem.ufl.edu/4411L_f00/i2_lif/ar_laser.html

After J. J. thompson, and Rutherfordand Milikan oil drop experiment

• Cathode rays and gold foil experiment

• J.J. Thompson- discovered the charge to mass ratio of the electron

• Milikan –Oil drop experiment discovered the electron charge-by which figured out the mass

• Rutherford and Gieger- said there is a dense positve nuclear charge

Strawberry model of atom

Nobel - Ernest Rutherford -http://www2.slac.stanford.edu/vvc/no

bel/rutherford.html

FOR MANY YEARS AFTER.

Now- Matter waves

The cloud model

• The cloud model represents a sort of history of where the electron has probably been and where it is likely to be going.

• The red dot in the middle represents the nucleus while the red dot around the outside represents an instance of the electron.

• Imagine, as the electron moves it leaves a trace of where it was.

.• This collection of traces quickly begins to resemble a

cloud. The probable locations of the electron predicted by Schrödinger's equation happen to coincide with the locations

specified in Bohr's model.

Erwin Rudolf Josef Alexander Schrödinger

• (German: English: ; 12 August 1887 –

• 4 January 1961) was an Austrian physicist and theoretical biologist who was one of the fathers of quantum mechanics, and is famed for a number of important contributions to physics, especially the Schrödinger equation, for which he received the Nobel Prize in Physics in 1933.

http://hyperphysics.phy-astr.gsu.edu/hbase/hyde.html

What is quantum mechanics?Used to predict the shape of the

electron cloud

The Postulates of Quantum Mechanics.

• Lecture 1– The Postulates of Quantum Mechanics. – Another source of QM Postulates.

• Lecture 2– Plots of some Legendre Polynomials on the interval x = [-1,1] – Pictures of spherical harmonics (absolute magnitudes) – Lecture 2 Highlights

• Lecture 3– Lecture 3 Highlights– Spherical Harmonic |Y2

m|2

• Lecture 4– Lecture 4 Highlights– H-Atom radial wavefunctions– H-Atom Orbitals– Notes on series solutions to differential equations

spherical harmonics (absolute magnitudes)

• The view of the atom is mathematical and philisophical??

• It is jus over the last 25 years do we now have very powerful instruments to say that predictions made were pretty accurate!

Desription of matter waves

• Common experience tells us that the behavior of waves is much different than the behavior of particles.

• Wave phenomema has many common examples, but all waves share some common features. Waves have a frequency, a wavelength, a wave velocity, and an amplitude, which may be examined in the following figure:

Einstein showed wave particle dualityof matter and light

• The photoelectric effect- metals have a work function

.

First describe light

wavelength l and the frequency n

For a given type of wave in a given medium, the wavelength l and the frequency n can be related to the speed of propagation of the wave(wave velocity) as follows:

• l n = c•

• For Light (electromagnetic waves) travelling in a vacuum, this speed of propagation is mighty quick:

• 2.99792 x 108 m/s. •

Light is just one portion (one range of frequencies) of the EM spectrum, which spans vastly diverse types of radiation:

• A device that separates light by its frequency is said to 'disperse' the light. Prisms and raindrops disperse light by refraction, gratings and holograms by diffraction.

PA prism: device that separates light by its frequency is said to

'disperse' the light. Prisms and raindrops disperse light by refraction, gratings and holograms by diffraction.

Pic of cd

6.2 Quantization: Planck, Einstein, Energy, and Photons.

• 6.2 Quantization: Planck, Einstein, Energy, and Photons.

• 3 things lead to this!!!

• The uv catastrophy

• The photoelectron effect

• Slit experiment-davisson and gilmer

6.2 Quantization: Planck, Einstein, Energy, and Photons.

• The uv catastrophy

6.2 Quantization: Planck, Einstein, Energy, and Photons.

• Slit experiment-davisson and gilmer

6.2 Quantization: Planck, Einstein, Energy, and Photons.

• Einstein showed wave particle dualityof matter and light

• By the The photoelectron effect

• When ultraviolet light falls on certain metals, electrons are emitted. This phenomenon in which certain metals emit electrons when exposed to light of suitable frequency, is called PHOTO ELECTRIC EFFECT. In short, ejection of electrons by means of light is called 'photo electric effect'

• Electrons ejected from a sodium metal surface were measured as an electric current. Finding the opposing voltage it took to stop all the electrons gave a measure of the maximum kinetic energy of the electrons in electron volts

What Einstein saw . . ..

• The number of photo electrons depends upon:1. The nature of material2. The frequency of incident radiation3. The intensity of incident radiation4. Potential difference b/w the electrons

Work Function

• Minimum amount of energy which is necessary to start photo electric emission is called Work Function. If the amount of energy of incident radiation is less than the work function of metal, no photo electrons are emitted. It is denoted by .

• Work function of a material is given by .It is a property of material. Different materials have different values of work function. Generally, elements with low I.P values have low work function such as Li, Na, K, Rb, and Cs.

Work Function

Frequency determines energy!!

• Heinrich Rudolf Hertz (February 22, 1857 –January 1, 1894) was a German physicist who clarified and expanded the electromagnetic theory of light that had been put forth by Maxwell. He was the first to satisfactorily demonstrate the existence of electromagnetic waves by building an apparatus to produce and detect radio waves

Unit of energy

Hertz = Hz = 1/s = s-

Electon volt=

Joules

Frequency

Nanometers

wavenumbers

propagation of electric action

• Hertz published his work in a book titled: Electric waves: being researches on the propagation of electric action with finite velocity through space.[3]

Through experimentation, he proved that transversefree space electromagnetic waves can travel over some

distance

wave vector-theory of wave packet

THRESHOLD FREQUENCY

• Threshold frequency is defined as the minimum frequency of incident light which can cause photo electric emission i.e. this frequency is just able to eject electrons with out giving them additional energy.It is denoted by

Must understand this principle

1. the intensity of light will not increase the number of electrons eject

2. The frequency of light determines the number when electrons will be ejected

3. The energy of light is determined by :

• C = l u= 3.00 x 108 m/s

l = lamda=wavelength

u= upsilon= frequency

Light is like a acordian

To the text

• 6.11 an energy of 3.3 x 10-19 J/atom is required to cause a cesium atom on a metal surface to lose an electron. Calculate the longest possible wavelength of light that can ionize a cesium atom.

• In what region of the spectrum does this radiation lie?

On MCAT

• 6.11 You are an engineer designing a switch that works by the photoelectric effect. The metal you wish to use in your device requires 6.7 x 10-19 J/atom to remove an electron.

• Will the switch work if the light falling on the metal has a wavelength of 540 nm or greater?

• Why or why not?

Your time line

• Electron Transitions

• The Bohr model for an electron transition in hydrogen between quantized energy levelswith different quantum numbers n yields a photon by emission with quantum energy: This is often expressed in terms of the inverse wavelength or "wave number" as follows: