Transcript Modern Physics - Milan Area Schools

Warm up
1. What are some of the dangers of
nuclear energy?
 2. Where does the energy for nuclear
reactions come from? (think of where the
word “nuclear” comes from/sounds like)

Atoms

Greeks: four elements
Earth, fire, wind, water
 What’s the smallest piece you can cut
something into?


Late 1800’s ‘discover’ the atom as the
smallest piece of stuff

Scientists new atoms were small, had mass,
and were electrically neutral
Electrons
Scientists discovered the electron
 They knew electrons had a negative
charge, and were in the atom.
 So where were the positive charges to
make atoms neutral?

Atomic models

Plum pudding model


J.J. Thomson
Solar system model
“The Bohr model” after N. Bohr
 E. Rutherford experiment

Energy levels

Electrons can only ‘orbit’ at certain levels
of energy.
Hydrogen Atoms
Orbital radius: rn = [h2n2] / [4(pi)2Kmq2]
 n = orbital level
 K = 9 * 109
 h = Planck’s constant
 q = electron charge
 m = mass of an electron

Energy of an electron
En = -13.6 eV * 1/n2
 eV = electron volt
 When an electron changes energy levels it
goes up or down by this amount. This is
Quantum physics: that means any photon
emitted or absorbed by an atom has that
energy.

Uses
Determining what stars are made of
 Determining what is between earth and a
star

Lasers
Light amplification by Stimulated Emission
of Radiation
 Excite an electron to a certain energy level
(pump). Then it relaxes to a lower, stable,
state. When it then jumps down to a its
base state it releases a photon of the
wavelength corresponding to the energy
loss. E = hf

Lasers
Coherent
 Monochromatic
 Directional
 USES


: measuring, cutting, reading music,
holograms, surgery
Reality
Electrons don’t ‘orbit’ nicely
 Electron Cloud
 Heisenberg’s Uncertainty Principle

Can know where
 Can know how much energy
 Can’t know both

Quantum Tunneling

Example of electron cloud and statistical
physics
Light Sabers

Properties
Hot
 Light
 ~ 4 ft long
 Deflect blaster bolts

Other future weapons
Rail guns
 Coil Guns

Radioactivity
Alpha Decay – Helium Nucleus
 Beta Decay – Electrons emitted from the
nucleus when a neutron turns into a proton
 Gamma decay – photon emission from
nucleus.
 ½ life – time it takes for half a substance to
decay away.

Nuclear Reactions

Fission
Chain Reactions
 Nuclear Power
 Atom bombs


Fusion
Stars
 Dream energy

Other uses of radiation
medicine
 chemotherapy
 power supplies
 plant mold killers.

Forces
Strong
 Weak

Faraday Cage
Dyson Sphere
Relativity

Time Dilation

Length Contraction

Time Travel
Homework
Review for Exam
 Make 1 page of notes to use
