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Quantum Theory, With Atomic and Nuclear Physics.

History of Atomic Models (I)

1. Single indivisible particle, “atomos” Greek.

Democritus(460-370 BC)

2. Plum Pudding Model

J.J. Thomson(1856-1940), England, used his CRT to discover the electron.

Some Early ApparatusThomson’s CRT (photo)

Schematic Drawing

Question: What does CRT stand for?

Cathode Ray Tube

Robert Millikan (1868-1953) and his Oil-Drop Experiment in 1909.

Proved that the elementary unit of charge, 1.6x10-19 C only occurred in certain amounts (Quantized).

History of Atomic Models (II)

3. Planetary Model - imagine the solar system with the Sun as the nucleus and the planets as the electrons.

Ernest Rutherford(1871-1937), England, Gold-foil Experiment. Results:

(1) most of the atom is empty space

(2) almost all the mass is in the nucleus.

The Rutherford Scattering(Gold Foil) Experiment

Contributors to the Photoelectric Effect and

Quantum Theory

Heinrich Hertz

1857-1894

Max Planck

1858-1947

Albert Einstein

1879-1955

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The Photoelectric Effect

• Light is sent to a metal surface. • If the frequency of the light is

high enough, the light kicks electrons off the surface of the metal.

• Emitter is connected to the negative terminal of a battery.

• Collector is attached to the positive terminal.

• Result: The Photocell.

Discovered for the first time by Max Planck and Heinrich Hertz, Germany, in the late 1800’s.

Carbon Arc Light

Photoelectric effect

Einstein put forward a theory:

• Light energy is quantized.• Light consists of a stream of particles called photons.• The energy of each photon (E) depends

on the frequency (f ) of the light.

Frequency increasing

GIVES ALL ITS ENERGY

TO ONE ELECTRON

e

ONE PHOTON

The emission of electrons from a material that is bombarded with radiation in the form of light.

Ephoton = hf with h = 6.6 x 10-34 J ·s LNK2LRN

The Explanation of

the Photoelectric Effect

Problem #1. Calculate the energy of a photon of light having a frequency of 2.5x1015 Hz.

(Show your work.)

Given: f = 2.5x1015 Hz

We know Planck’s Constant.

h = 6.6x10-34 Js

E = ___________

Equation: E = hf

Solution: E = 6.6x10-34 Js · 2.5x1015 Hz

E = 1.7x10-18 J

All parts of the Electromagnetic Spectrum move at the same speed through a vacuum: 3.0 x 108 m/s.

We call this the speed of light and assign it the letter, c .

But all possess the 5 properties of waves, so they must obey the wave equation, c = f·λ .

The energy is carried by mass-less photons, and computed with the equation, E = h•f . ( h = 6.6 x 10-34 Js )

Summary of the Equations for Photoelectric Effect and Quantum TheoryE = h·f Energy of a photon of light

h = 6.6 x 10-34 J ·s

c = f · Wave equation for light, c = 3.0 x 108 m/s

Wo = h·foWork function, with fo = threshold frequency

KEmax = q·VoMaximum kinetic energy of photoelectrons based on stopping potential, Vo

KEmax = E - WoMaximum kinetic energy of photoelectrons based on photon energy and work function

E = mc2Einstein’s equation for conversion of matter to energy

Combine these three equations to get a single equation for the wavelength of a matter particle.

E = mc2 c = f · E = h·f

The equation is: = h / (mv)

“If waves (light) can act like particles, why can’t particles act like waves”.

Prince Louis Victor deBroglie (1892-1987), France.

Matching Exercise.

• Democritus

• J. J. Thomson

• Ernest Rutherford

• Robert Millikan

• Max Planck

• Heinrich Hertz

• Albert Einstein

• Found charge on electron with Oil-drop experiment

• Unit of frequency named after him

• Made the first CRT• Gave us the equation E =

mc2

• Atom is single indivisible particle

• Planetary atomic model• His constant is 6.6x10-34 Js

Can you then come-up with the equation for the momentum of a photon? Remember, if particles can act like waves, why can’t waves act like particles?

The equation is: p = h /

Useful constants: 1 eV = 1.6 x 10-19 J

mass of electron = 9.11 x 10-31 kg

mass of proton = 1.67 x 10-27 kg

charge on the electron = -1.6 x 10-19 C

charge on the proton = 1.6 x 10-19 C

Problem #2. Calculate the threshold frequency of a metal having a work function of 6.4 eV.

(Show your work.)

Given: Wo = 6.4 eV

We know Planck’s Constant.

h = 6.6x10-34 Js

fo = ___________

Equation: Wo = hfo

Solution: fo = Wo / h

= (6.4 eV x 1.6 x 10-19 J / 1 eV) / 6.6x10-34 Js

fo = 1.6x1015 Hz

Problem #3. A metal has a threshold frequency of 3.3 x 1014 Hz. Light with a frequency of 2.0 x 1015 Hz shines on the metal. Find the maximum kinetic energy of the photoelectrons. (Show your work.)

Given: fo = 3.3x1014 Hz f = 2.0x1015 Hz

Planck’s Constant, h = 6.6x10-34 Js

KEmax = ___________

Equation: KEmax = hf – hfo = h(f – fo )

KEmax = 6.6x10-34 Js(2.0x1015 Hz – 3.3x1014 Hz ) KEmax = 1.1x10-18 J

Problem #4. Calculate the de Broglie wavelength of a cannon ball with a mass of 100.0 g and a velocity of 7.0x102 m/s. (Show your work.)

Given: m = 100.0 g = .1000 kg

v = 7.0x102 m/s λ = ___________

Equation: λ = h/mv h = 6.6x10-34 Js

Solution: λ = 6.6x10-34 Js / (.1000 kg ·7.0x102 m/s)

λ = 9.4x10-36 m

History of Atomic Models (III)

4. Planetary-Quantum model was proposed to align atomic theory with the new physics of Quantum Theory.

Niels Bohr(1885-1962), Denmark, determined the equations for rn = 5.3 x 10-11 m x n2 and En = -13.6 eV x 1/n2

The Bohr Model - Planetary Quantum

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Henri Becquerel (1852-1908)

The Discovery of Radioactivity

ALPHA

BETA

GAMMA

Nuclear Physics.

Nuclear Physics.

X-Ray Production by Wilhelm Röntgen (1895)

The Geiger-Muller Tube (Geiger Counter). demo

Antoine Henri Becquerel    

1/2 of the prize (France)

The Nobel Prize in Physics 1903

"in recognition of the extraordinary services he has rendered by his discovery of spontaneous radioactivity"

"in recognition of the extraordinary services they have rendered by their joint researches on the radiation phenomena discovered by Professor Henri Becquerel"

Pierre Curie   France    1/4 of the prize

Marie Curie, née Sklodowska France 1/4 of the prize

Contributors to the Study of Nuclear Physics

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