6 from atoms to color tv

Big Questions in Science

Big Questions in Science, fall 2012. SdH, AUC 2

Color and spectra Atoms Schrödinger’s cat Radioactivity

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Light is a wave made of different wavelengths Blue light has short wavelength. Scattered all around atmosphere.

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Ni (78%) O (21 %)

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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

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)

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

Big Questions in Science, fall 2012. SdH, AUC 9

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

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

Rutherford: second, “planetary” model (inspired by Lord Kelvin).

13 Big Questions in Science, fall 2012. SdH, AUC

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Different elements have different ‘absorption spectra’, specific wavelengths that they absorb (or emit).

16

Planck’s law

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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

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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Radiatioactive decay is random. Same true for photon emission by atom:

unpredictable.

Big Questions in Science, fall 2012. SdH, AUC 20

21

PET scan X-rays

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

The single-slit experiment

Big Questions in Science, fall 2012. SdH, AUC 23

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http://www.universetoday.com/83380/double-slit-experiment/

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http://www.hitachi.com/rd/research/em/doubleslit.html

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.

Big Questions in Science, fall 2012. SdH, AUC 27

http://micro.magnet.fsu.edu/primer/java/interference/doubleslit/

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

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

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

31

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

Big Questions in Science, fall 2012. SdH, AUC 32

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Big Questions in Science, fall 2012. SdH, AUC 34

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