6 From Atoms To Color TV
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Transcript of 6 From Atoms To Color TV
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Big Questions in Science
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Big Questions in Science, fall 2012. SdH, AUC 2
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Color and spectra Atoms Schrödinger’s cat Radioactivity
Big Questions in Science, fall 2012. SdH, AUC 3
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Light is a wave made of different wavelengths Blue light has short wavelength. Scattered all around atmosphere.
Big Questions in Science, fall 2012. SdH, AUC 4
Ni (78%) O (21 %)
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Big Questions in Science, fall 2012. SdH, AUC 5
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Cathode ray tube 1. Three electron guns 2. Electron beams 3. Focusing coils 4. Deflection coils 5. Anode connection 6. Separating beams 7. Phosphor layer 8. Close-up of screen
Big Questions in Science, fall 2012. SdH, AUC 6
http://en.wikipedia.org/wiki/File:CRT_color_enhanced.png
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7 Big Questions in Science, fall 2012. SdH, AUC
• (Semi-) vacuum tube • Metal electrodes, high voltage in between • Postitively charged atoms attracted to cathode (neg.) • Kicked off electrons attracted to anode (positive charge)
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Faraday: electrical current bent by a magnet. Thomson: electrical current consists of
particles much smaller than atoms. Mass 1600 smaller than hydrogen. Röntgen: new type of ‘cathode’ radiation.
Becquerel: uranium emits Röntgen radiation. Marie Curie researched other substances.
Big Questions in Science, fall 2012. SdH, AUC 8
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Big Questions in Science, fall 2012. SdH, AUC 9
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Ernest Rutherford: radiation consists of:
Beta-rays. Could be bent, electrons.
Alpha-rays. Could be bent, much
heavier, positive charge. Helium ions.
Gamma-rays. Röntgen radiation. UV
Suggested internal structure of atoms.
10 Big Questions in Science, fall 2012. SdH, AUC
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Rutherford: researched thorium, found emanation and radioactivity. Bombarded platinum foil with alpha particles, reflected in all directions.
Conclusion: mass concentrated in the nucleus.
12 Big Questions in Science, fall 2012. SdH, AUC
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Rutherford: second, “planetary” model (inspired by Lord Kelvin).
13 Big Questions in Science, fall 2012. SdH, AUC
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Big Questions in Science, fall 2012. SdH, AUC 14
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Big Questions in Science, fall 2012. SdH, AUC 15
Different elements have different ‘absorption spectra’, specific wavelengths that they absorb (or emit).
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16
Planck’s law
Big Questions in Science, fall 2012. SdH, AUC
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17
Assumption Planck needed to make: light carries energy in discrete amounts.
Each ‘energy packet’ has energy h
Big Questions in Science, fall 2012. SdH, AUC
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Fascinated by planetary model. Putting things together: quantum hypothesis
applied to atom. Atomic numbers explain properties of atoms. Sommerfeld refined version.
18 Big Questions in Science, fall 2012. SdH, AUC
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Big Questions in Science, fall 2012. SdH, AUC 19
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Radiatioactive decay is random. Same true for photon emission by atom:
unpredictable.
Big Questions in Science, fall 2012. SdH, AUC 20
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PET scan X-rays
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As long as radiation is not measured, the atom is in two states (decay/non-decay). This is called a superposition.
Property is only determined once a measurement is made.
Big Questions in Science, fall 2012. SdH, AUC 22
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The single-slit experiment
Big Questions in Science, fall 2012. SdH, AUC 23
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Big Questions in Science, fall 2012. SdH, AUC 24
http://www.universetoday.com/83380/double-slit-experiment/
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Big Questions in Science, fall 2012. SdH, AUC 25
http://www.hitachi.com/rd/research/em/doubleslit.html
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26 http://russherman.com/Talks/FirstThreeMinutes_CollegeDay.pdf
Big Questions in Science, fall 2012. SdH, AUC
Waves that go through the slits interfere with each other.
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Big Questions in Science, fall 2012. SdH, AUC 27
http://micro.magnet.fsu.edu/primer/java/interference/doubleslit/
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Electrons and photons behave as waves while in transit: interference.
Detected as particles on the screen. Interference pattern disappears if
observation. No way to predict where single photon ends
up: intrinsic unpredictability. Only probabilities.
Big Questions in Science, fall 2012. SdH, AUC 28
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de Broglie: if photons are both waves and particles, particles behave as waves.
Planck relation:
. Matter:
.
Frequency proportional to speed (squared).
Big Questions in Science, fall 2012. SdH, AUC 29
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Waves of high frequency (short wavelength) are sharply localized, waves of low frequency (long wavelength) are spread out.
Big Questions in Science, fall 2012. SdH, AUC 30
Small
Large
Large
Small
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Electron microscope
Resolution ~ wavelength 0.1 to 0.5 nm
http://www.science.uva.nl/onderwijs/thesis/apart/phys/thesis.php?start=181&level=bachelor
Quantum computing
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Big Questions in Science, fall 2012. SdH, AUC 32
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Big Questions in Science, fall 2012. SdH, AUC 33
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Big Questions in Science, fall 2012. SdH, AUC 34
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Compare Bohr’s model of the atom with the Solar System.
1) Similarities. 2) Where analogy breaks down.
What is the role of the hydrogen atom in the development of modern quantum mechanics?
Hint: consider Kuhn’s notion of ‘exemplar’.
Think of similar examples in Newtonian physics and in the theory of relativity.
Big Questions in Science, fall 2012. SdH, AUC 35