Chapter...

7/27/2019 Chapter 27bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb

http://slidepdf.com/reader/full/chapter-27bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb 1/29



Day 1

Learning Goals

Understand the relationship betweenwavelength and intensity for blackbodyradiation

Understand how Planck’s Hypothesisexplained the relationship between

wavelength and intensity for blackbodyradiation



Classical Theory on Radiation

Thermal Radiation

What is it?How does it occur?



Classical Theory on Radiation

Blackbody Radiation

What is it?

How does it work?Graph of Intensity of BBR vs. Wavelength

The Ultraviolet Catastrophe



BBR vs Wavelength



Super Max ( Max Planck )

1858 – 1947

He Provided the Explanation for thespectral distribution of Blackbody

Radiation (1900 )

Awarded the Nobel Prize in 1918



History of Blackbody

Radiation

http://www.electro-

optical.com/bb_rad/bb_rad.htm

http://galileo.phys.virginia.edu/classes/252/black_body_radiation.html

http://www.electro-optical.com/bb_rad/bb_rad.htm











Day 2

Learning Goals

Understand how the photoelectric effect

gives credence to the particle theory of

light

Know how to use the work function to

solve problems involving thephotoelectric effect



The Photoelectric Effect

When light is incident on certain metallic

surfaces, electrons are emitted

Photoelectrons

Hertz

Einstein’s (1905) explanation



Photoelectric Effect




Graph of photoelectric current vs.

potential difference (DV)

Current dependent on intensity

Current dependent on, DV




Stopping Potential

KEmax = eDVs

Independent of the radiation intensity

Work Function

Cutoff Wavelength

lc = c/f c = hc/f




Wave Theory couldnot explain: Cutoff Frequency

KEmax independentof intensity

KEmax increases withlight frequency

Electrons are emitted

instantaneously

Photon Theoryaccounts for: f, the work function

KEmax = hf – f

Depends only on lightfrequency

1 - 1interaction b/wphotons and

electrons Linear relationship

b/w f and KEmax



Applications of the Photoelectric

Effect

Photoelectric Cell

Street lights

Breathalyzer



Day 3

Learning Goals

Understand the nature and production

of x-rays so you can:

Calculate the shortest l of x-rays that may

be produced by electrons accelerated

through a specified voltage



X-RAYS

Wilhelm Roentgen first noticed them in1895 while studying electricaldischarges

Characteristics of x-rays

Traveled at or near the speed of light

Were not deflected by electric or magneticfields



X-RAYS

In 1912 Max von Laue suggested

diffracting x-rays

Used atomic crystal lattice as a diffraction

grating

determined the wavelength of x-rays to be

about 0.1 nm



X-RAYS

The Production of x-rays Electrons are accelerated through a DV of several

thousand volts

Electrons collide with a metal plate

X-rays are the energy emitted when the electronsare decelerated, but why are they decelerated?

Threshold voltage



X-RAYS

Graph x-ray intensity vs. wavelength

Continuous broad spectrum dependent onthe applied voltage. Why?

Characteristic spikes in the graph aredependent on the target material

lmin = hc/(eDV) Shortest wavelengthradiation that can be produced



Day 4

Learning Goals

Understand the concept of Compton

scattering so you can

Describe Compton’s experiment, state the

results, and how these results are

explained

Account for the increase of photon

wavelength, and explain the significance of the Compton wavelength



The Compton Effect

Compton’s Experiment X-ray beam of a specified wavelength, l0, directed

at a block of graphite

Result was the scattered x-rays had a longer wavelength, l,

Amount of energy reduction depended on the

angle at which the x-rays were scattered

The change in wavelength, Dl, is the ComptonShift.



The Compton Effect

Compton’s Explanation

Photon particle collision similar to billiard

ball collisions. Which means what?

Dl = l – l0 = h/(mec) *(1 – cos q )

Compton Wavelength, h /(mec), is very

small compared to visible light.



Day 5

Learning Goals

Understand the concept of DeBroglie

wavelength so they can:

Calculate the wavelength of a particle as a

function of its momentum

Describe the Davison-Germer experiment,

and explain how it provides evidence for

the wave nature of electrons



Pair Production & Annihilaiton

Energy of a photon is convertedcompletely into mass, pair production

Electron and positron are created froma photon

Energy, momentum, & charge areconserved



Pair Production & Annihilaiton

Minimum energy required to produce a

positron

hf min

= 2me

c2 ( E = mc2)

Pair production cannot occur in a

vaccum, but can only occur in the

presence of a massive particle

(nucleus)



Pair Production & Annihilation

Pair Annihilation: electron-positron pair

produce two photons

Momentum has to be conserved



Davison-Germer Experiment

Double slit experiment shooting

particles at a double slit

E id t S t th

http://phys.educ.ksu.edu/vqm/html/doubleslit/index.html






Evidence to Support the

Particle Theory of Light

Photoelectric Effect

Compton Effect

X-Rays

Pair Production & Annihilation

Chapter...

Documents

Transcript of Chapter...