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Audio 0:12:13.134181
“… an act of despair … I was ready to sacrifice any of my previous convictions about physics …”
Energy (light) is emitted or absorbed in discrete units (quantum).
- Audio 0:12:39.255151
- “One of the 7 or 8 numbers that define our universe”
“a purely formal assumption … actually I did not think much about it…”

Audio 0:13:59.822330
“for his services to Theoretical Physics, and especially for his discovery of the law of the photoelectric effect” 1921
- Light has both:
  1. wave nature
  2. particle nature
Photon is a “particle” of light
- Audio 0:15:56.294916
- Photo electrons are emitted as soon as you turn the light on is explained by the photon description
Predicted that KE would be linearly dependent upon frequency
hv = KE + BE
KE = hv - BE

Audio 0:16:45.896720
When copper is bombarded with high-energy electrons, X rays are emitted. Calculate the energy (in joules) associated with the photons if the wavelength of the X rays is 0.154 nm

Audio 0:22:58.445126
A photon has a wavelength of 624 nm. Calculate the energy of the photon in joules
Are there any extra reviews before the test?
- Audio 0:27:22.163854
- Some of Wednesday’s lecture will be review
- Also, there’s practice on the MyLabsPlus website

Audio 0:28:51.812590
Light had been thought of as a wave for a long time and now it’s being thought of as particles
- People were asking why is light emitted and absorbed in fixed quantities?

Audio 0:30:24.253251
Each element has its own emission spectrum
All of this points to atoms emitting and absorbing light / energy in discrete packets

Audio 0:31:23.054768
The nuclear model of the atom (Rutherford model) does not explain what structural changes occur when the atom gains or loses energy.
- He hypothesized that only certain orbits are allowed and came up with a model which predicted what was observed
Bohr developed a model of the atom to explain how the structure of the atom changes when it undergoes energy transitions.
Bohr’s major idea was that the energy of the atom was quantized, and that the amount of energy in the atom was related to the electron’s position in the atom.
- Quantized means that the atom could have only very specific amounts of energy.

Audio 0:32:22.750198
The electrons travel in orbits that are at a fixed distance from the nucleus.
- Found different shapes of orbits
- Stationary states
- Therefore, the energy of the electron was proportional to the distance the orbit was from the nucleus.
Electrons emit radiation when they “jump” from an orbit with higher energy down to an orbit with lower energy.
- Audio 0:32:58.969212
- The emitted radiation was a photon of light.
- The distance between the orbits determined the energy of the photon of light produced.

Audio 0:33:46.737388
1. e- can only have specific (quantized) energy values
2. light is emitted as e- and moves from one energy level to a lower energy level
n (principal quantum number) = 1,2,3,…
RH (Rydberg constant) = 2.18 x 10-18J

Audio 0:35:34.154227
Only worked for Hydrogen, Li 2+, and Be 3+
Only for a nucleus and one electron
When charges are forced through curved path they emit radiation (Bermsstrahlung) so “orbits around nuclei are unstable”

Audio 0:36:55.247976
Einstein says light has wave and particle properties
Now we think maybe particles have wave properties
The interaction between waves (e.g., electromagnetic, ocean) is called interference.
Interference Types:
- Constructive interference: waves that interact so that they make a larger wave are said to be in phase
- Destructive interference: Waves that interact so that they cancel each other out are said to be out of phase

Audio 0:38:41.975443
When traveling waves encounter an obstacle or opening in a barrier that is about the same size as the wavelength, they bend around it; this is called diffraction.
- Traveling particles do not diffract
The diffraction of light through two slits separated by a distance comparable to the wavelength results in an interference pattern of the diffracted waves.
An interference pattern is a characteristic of all light waves.

Audio 0:39:38.320960
De Broglie proposed that particles could have wavelike character.
De Broglie predicted that the wavelength of a particle was inversely proportional to its momentum.
Because it is so small, the wave character of electrons is significant.
De Broglie relation

Audio 0:40:32.639227
What are the de Broglie wavelengths (in nm) associated with an electron traveling at 6.0 * 10^5 ms-1 and a 52.5 g Ping-Pong ball traveling at 15.6 m/s?

Term	Definition
wave particle duality of light	describes that light acts like a wave and a particle in different scenarios
photon	particle of light
quantized	Property of atoms meaning that the atom could have only very specific amounts of energy
constructive interference (in phase)	occurs when waves that interact so that they make a larger wave
destructive interference (out of phase)	occurs when waves interact so that they cancel each other out
diffraction	occurs when waves bend around an obstacle or opening in a barrier which is about the same size as the wavelength