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Quantum Mechanics

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Quantum mechanics picks up where classical mechanics leaves off ... What's the difference between the different types of balls? ... – PowerPoint PPT presentation

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Title: Quantum Mechanics


1
Quantum Mechanics
  • And
  • Spectral Lines

2
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3
Start of the Story
  • When something is mechanical, it does not change.
  • Engines

4
Start of the Story
  • When something is mechanical, it does not change.
  • Engines
  • Tools

5
Start of the Story
  • When something is mechanical, it does not change.
  • Engines
  • Tools
  • Light switch

6
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What do you think of mechanical?
  • Physicists and chemists use the word
    mechanistic
  • Any ideas?

8
Newton
  • Figured out cool rules
  • Force, gravity, pendulums
  • Others were figuring out optics and light, where
    the planets were, their orbits, etc.

9
Laws of the Natural World
  • Newtons laws still hold for large scale
    physics-they are called classical physics

10
Breakthroughs.
  • Experimental techniques
  • Technologies
  • Led to theoretical breakthroughs

11
Breakthroughs.
  • At subatomic levels
  • At speeds close to the speed of light
  • Things did not behave according to classical
    physical laws

12
Breakthroughs.
  • The main new ideas were that 1)the universe was
    NOT mechanistic, unchanging it was expanding,
    moving, dynamic

13
Breakthroughs.
  • The main new ideas were that
  • 2) inside the atom, there was uncertainty
    about the location and speed of electrons around
    the nucleus- UNPREDICTABILITY arrived!

14
Here are the players and the story
  • Quantum mechanics picks up where classical
    mechanics leaves off
  • Actually, everything obeys quantum mechanics, you
    just cant see it except at the subatomic level

15
Max Planck
  • Looked at spectral lines
  • Decided energy changes in packets or quanta

16
Max Planck
  • His formula
  • Ehv
  • Energy
  • Plancks constant times frequency of the light
    wave

17
Oh
  • He won a Nobel Prize for this idea

18
Albert Einstein
  • If Planck was right, light should also have
    particle properties

19
Photoelectric Effect
  • Take a slab of a metal
  • Shine a light( photons) at it
  • Some lights (photons) will energize the electrons
    and they will leave

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However,
  • Some lights you can shine all day and electrons
    will NEVER leave

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Why?
  • Here is an analogy build a wall of bricks
    without mortaring them together. Just stack them
    up.Now throw a ping pong ball at them. Will they
    ever fall down?

25
Why?
  • What about a tennis ball? No- or a baseball at
    the same speed? Yes, some will fall over
  • What about a steel ball? Yep, you could knock
    them all down if you had the time.

26
Why?
  • Whats the difference between the different types
    of balls?
  • Their ENERGY is different because of their mass
  • KE1/2 mass times velocity squared!

27
Why?
  • Whats the ENERGY relationship in light? Einstein
    said it was
  • Energy equals Plancks constant times the
    frequency of the waves

28
Why?
  • Whats the ENERGY relationship in light? Some
    frequencies did not deliver the right kind of
    ball, or in physics language, quanta.

29
Lets look at this picture again
  • Which are the high energy light waves (high
    frequency) and which are the low energy waves
    (low frequency)?

30
Electromagnetic spectrum
  • Heres another visual of the energy of light
    quanta (photons)

31
Which are the
  • Ping pong balls
  • Tennis balls
  • Baseballs
  • Steel balls

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Einstein said
  • No matter how intense or how long you shined a
    red light on the metal, NO electrons would be
    ejected! The quanta (ping pong balls) did not
    have enough energy.

34
Einstein said
  • Since the red light energy could not accumulate
    to make enough energy, it must be a limited
    amount of energy packet (quanta)

35
Einstein
  • Proved that light has particle properties and
    that photons are absorbed in individual packets
    of energy (quanta)

36
Oh
  • He won a Nobel Prize for this idea

37
Nobel Prizes
  • This picture was at the Nobel ceremony in Sweden

38
Niels Bohr
  • was trying to explain the emission spectrum of
    hydrogen, those pesky black lines

39
Niels Bohr
  • Why were they always the same?
  • Why werent they continuous like regular light?

40
Niels Bohr
  • Influenced by Max Planck, his idea of packets, he
    figured that electrons stayed in specific energy
    levels in the atoms, not inbetween

41
Niels Bohr
  • The spectra he saw were electrons jumping to
    energy levels with different energies
  • Nothing in between

42
Niels Bohr
  • When they dropped back down to their normal
    level, they gave off light with different
    wavelengths
  • Which we see as colors in the visible
    electromagnetic spectrum

43
Electromagnetic spectrum
  • energy is proportionate to frequency
  • Color shows its energy

44
Electromagnetic spectrum
  • Heres another visual of the energy of light
    quanta (photons)

45
Hydrogen emission spectrum
  • This is what he saw when hydrogen was excited

46
Niels Bohr
  • He thought the excited electrons were jumping to
    one of the allowable energy levels.
  • And them emitting the excess energy as photons
    when they dropped back to normal

47
Niels Bohr
  • The colors would differ with different element
    a fingerprint

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50
Colors proving energy levels
51
Niels Bohr
  • Electrons are in discrete energy levels
  • An energized electron can jump to a higher energy
    level and drop back its normal one and emit the
    energy in discrete quanta (photons) we see as
    colors

52
Oh
  • He won a Nobel Prize for this idea

53
Moving the story along a little faster
  • Along comes Louis de Broglie
  • He reasons that if light can have particle and
    wave properties, so can MATTER!

54
Louis de Broglie
  • The electron is a spherical standing wave motion
    of space

55
Standing wave energy levels
56
Louis de Broglie
  • This sets in motion the movement of quanta or
  • quantum mechanics

57
Oh
  • He won a Nobel Prize for this idea

58
Werner Heisenberg
  • He said the language of mathematics lets us blend
    the wave and particle nature of light and matter
  • quantum theory

59
Werner Heisenberg
  • When we do this we introduce uncertainty

60
Werner Heisenberg
  • We cannot measure the wave nature (speed) and
    particle nature (location) simultaneously

61
Werner Heisenberg
  • Heisenberg Uncertainty Principle- was this guy
    smart or what!

62
Oh
  • He won a Nobel Prize for this idea

63
Our last quantum persona
  • Erwin Schrodinger- found that the emission
    spectrums of multi-electron atoms could not be
    explained as simply as the hydrogen emission
    spectrum

64
Our last quantum persona
  • Erwin Schrodinger- found that the emission
    spectrums of multi-electron atoms could not be
    explained as simply as the hydrogen emission
    spectrum

65
Erwin Schrodinger
  • Electrons exist in clouds where the electrons
    location cannot be precisely predicted
  • Probability shapes the clouds

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Electron cloud pictures
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Schrodinger
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Erwin Schrodinger
  • Explained emission spectrum of multi-electron
    atoms
  • Famous for his quantum wave equation

74
Oh
  • He won a Nobel Prize for this idea

75
The End of the Story for now.
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