Is light a wave or
is light a
particle!?!
Experiment 1:
Experiment:
Light is incident on two closely spaced slits and the pattern
is observed on a wall or screen across the room.
Young’s Double Slit Experiment
expectations
If light was a particle (think
painted tennis balls)…
If light was a wave (think
water)…
• what pattern would you
• what pattern would you see see on the wall?
coming out of the double
slits?
Double Slit
Experiment
Light behaving like a
wave.
Notice the light and
dark fringes.
What do the dark
spots represent?
What to the light
spots represent?
What do the spots
with no spots
represent?
Wave moving through a
double slit and exhibiting
interference
Young’s Double Slit
Experiment:
Shows that light
behaves like a wave
Experiment 2:
Experiment:
Light is incident on a piece of metal.
Photoelectric Effect
If light was a particle (think
If light was a wave (think
painted tennis balls)…
water)…
• How would the energy of a • How would the cartoon get
more electrons to fly of the
ocean wave (amplitude)
metal?
affect the speed at which
the electrons get kicked out?
The Photoelectric Effect:
The Photoelectric Effect:
The Photoelectric Effect:
Shows that light behaves
like a particle
Is light a wave or is light
a particle!?!
AIM: How do we describe a particle of light?
• Do Now: which experiment shows light is a wave
and which experiment shows light is a particle?
What do we call a particle of light?
A PHOTON!!
•
A photon is a small ‘packet’ of light
•
Any single photon has a fixed, discrete energy.
•
The intensity of visible light can be increased or
decreased only by changing the number of photons
present.
•
The same rules hold true for all electromagnetic waves
outside the visible range.
Discrete Energy??
• Discrete energy is like money, you can only have integer multiples of
a minimum amount.
– For money, what is this minimum amount?
• A photon can only carry integer numbers of a minimum energy
– This minimum energy is denoted by Planck’s constant
• h= 6.63x10-34Js
• Planck’s constant is modern physics’ version of the
penny
• The energy of a photon is determined by its frequency (and
wavelength)
E  hf
E
hc

Units
A joule is a large unit of energy. When you are talking about
small electron, we use an electron volt instead
-19
1eV=1.6x10 J
Ex1. A photon has 3.5eV of energy. How many Joules of
energy is that?
Ex2. A photon has 4.8x10-19J of energy, how many electron
volts is that?
Examples
1. A photon of light has a frequency of 2.5x1014 Hz.
-
What is the energy of that photon in Joules?
What is the energy of that photon in eV?
2. A photon has a wavelength of 575nm
-
What is the frequency of that photon?
What is the color of the photon?
What is the energy of that photon in Joules?
What is the energy of the photon in eV?
AIM: How has our understanding of
the atom changed over the years?
DO NOW: Draw AND label a diagram of an atom.
Quiz…?
Atomic Structure
A brief History
Democritus- Greek Philosopher
~300BC
• The word atom means smallest piece.
Something that can not be divided.
• Atoms are made of the same ‘stuff’ but differ
in size and shape
• Atoms are in constant motion
• Atoms can combine to form different types of
matter
John Dalton
Late 1700s
• All elements are made up of atoms
• Atoms of the same element are all the same
but differ from atoms of different elements.
• Atoms can group together to form molecules
• Chemical reactions are changes in
combinations of atoms, not changes in the
individual atoms themselves.
JJ Thomson
late 1800s
• Measured the
charge/mass ratio of an
electron.
• Determined that an
electron had a negative
charge
• Could NOT determine the
actual mass or charge of
an electron.
• Plum pudding model of
the atom
Negative ‘plums’
Positive Goop
Rutherford-Geiger-Marsden
1911
• Gold foil scattering experiment
– Fired positively charged alpha particles (2 protons and 2
neutrons) at a thin foil of gold.
– Most alpha particles traveled straight through
• Most of an atom is empty space
– One day, one scattered at a wide angle as if it hit
something massive and dense.
• Holds most of the mass of an atom
• Must be positively charged
– This massive and dense thing was called the nucleus.
– An atom’s diameter is MUCH larger than that of the
nucleus.
Rutherford Scattering Setup
Most particles go straight through. A few scatter and
light up the screen at other angles.
Bohr (Orbital) Model
• Electrons orbit around
a central nucleus
– The electron orbitals
have definite (discrete)
energy levels.
– Electrons can not exist
between energy levels.
• Similar to the fact that
you can not stand
between rungs of a
ladder.
Bohr (Orbital) Model
• Ground states
– Electrons want to fill the
lowest possible levels so that
the atom stays stable.
• Excited states
– Electrons can ‘jump’ up
energy levels only if the
correct amount of energy is
absorbed by the electron.
– This amount of energy is
determined by the energy
difference in the atom’s levels.
Cloud Model
• The electrons do not exist in
definite orbits around the
nucleus like suggested, they
live in clouds where there is
a high probability that they
will be in a certain place.
Other regens have a low
probability.
Bohr: The Hydrogen Atom
1. What is the energy of the n=3
energy level in the hydrogen
atom?
a. What is this energy in
Joules?
2. What is the energy difference
between the n=1 and n=4
energy levels?
Hydrogen Absorption Spectrum
When light is incident on a hydrogen atom, it can absorb
the photons with the correct amount of energy that
allow the electrons in the atom to ‘jump’ to their
excited states. An absorption spectrum is the rainbow
of colors with the colors matching the correct energy
jumps missing.
Hydrogen Absorption Spectrum
1. Pick one of the missing colors
2. Determine a possible frequency of that color using
the RTs
3. Calculate the energy a photon of that color
4. Convert that photon’s energy into eVs.
5. Using your RTs decide which energy level
transition could be caused by that photon.
Hydrogen Emission Spectrum
Once an electron has reached the excited state by
absorbing the correct amount of energy. The electron will
stay there for a moment then return back down to the
ground state. When the electron falls back to the ground
state, it emits a photon with an energy equal to the
energy difference between the level it came from and the
level it went to.
Hydrogen Emission Spectrum
1. Pick a different color than before.
2. Determine a possible frequency of that color using
the RTs
3. Calculate the energy a photon of that color
4. Convert that photon’s energy into eVs.
5. Using your RTs decide which energy level
transition could be caused by that photon.
All Hydrogen Emissions
I was doing some particle physics research and I discovered 7 new
elements. I knew that each element was different because
_______________________________________.
I was able to draw diagrams of each element’s energy levels to scale,
and I was able to name each element’s spectrum, but I was not able
to match the element’s energy level diagram to its corresponding
spectrum.
Your goal is to use the scaled drawing to figure out the letter of that
element based on the atomic spectra pictured.
a. Show all calculations in an organized manor including formulas and
units.
b. Choose a fourth color for the spectrum and add the corresponding
fourth energy level to the element’s diagram. (it must be drawn to
scale)
B
A
E
D
C
F
G
How do LASERS work?
What is Coherent Light?
NOT coherent
-Many frequencies (colors)
- Different phases
NOT coherent
-Same frequencies (colors)
- Different phases
Coherent
-Same frequencies (colors)
- Same phases
The Standard Model of
Particle Physics
Things smaller than
protons and neutrons
Quarks
The building blocks of Protons and Neutrons
• A proton is made
up of two up
quarks and a
down quark (uud)
• A neutron is made
up of two downs
and an up (udd)
Antiparticles
• Antiparticles have the same mass as their particle ‘buddies’
just the opposite charge and quark make up.
• If a particle and an antiparticle collide, they annihilate each
other and all the mass is converted into energy.
1. What is the quark make up of an antiproton?
2. If a neutron and antineutron collide and annihilate each other,
how much energy is released in Joules?
Classification of Matter
Protons and
neutrons have 3
quarks, so they are
Baryons!
Mesons are any
particle with a
quark and
antiquark
Leptons
• Electrons are
leptons!
Make up your own particles
1.
2.
3.
4.
5.
6.
A baryon with a +1 charge
A baryon with a -2 charge
A meson with a neutral charge
A meson with a -1 charge
A baryon with a +3 charge
A meson with a -2 charge
Nuclear Physics
Subatomic Forces and
Structures
Zooming in on the
World Around Us
Macroscopically- really big
• Gravity
–holds all objects with mass together (from stars to dust)
• Electromagnetic Force
–Holds the (negatively charged) electrons in orbit around the
(positively charged) nucleus of an atom
• Strong Force
– Holds all the positively charged protons and neutral neutrons
together in the nucleus
• Weak Force
–Holds all the quarks together in a proton and neutron
Microscopically – really small
Force Name
Relative
Strength
Force Range
Force acts on
Very
Nucleons
Short
Very
quarks
Short
Strong Force
1
Weak Force
3
Electro-magnetic
Force
2
Infinite Charges
Gravitational Force
4
Infinite
Mass
Creating Nuclear Energy
Mass or energy can never be created or destroyed, only
converted from one to the other!
E  mc
2
Units of Mass
• Kilograms: for larger objects
• AMU (atomic mass units) sometime just u for short: The mass
of very small things
– Proton: 1.007u
– Neutron: 1.009u
• To convert mass in kilograms to energy in Joules used E=mc2
• To convert mass in u into energy in eV use the conversion in
your Reference tables (1u=931MeV) **1MeV=1,000,000eV**
Creating Nuclear Energy
Mass or energy can never be created or destroyed, only
converted from one to the other!
E  mc
Fusion
• Two smaller elements
(anything below iron) fuse
together to create a larger
element.
• This is favored by nature
because this process
releases energy.
2
Fission
• One larger element
(anything above Iron) split
apart to create two smaller
elements.
• This is favored by nature
because this process also
releases energy
Fusion up Close
• For light elements (up to Iron), fusing two elements
together creates a larger element and energy.
• This energy comes from the ‘missing’ mass.
– The larger element has a smaller mass then the total mass of the
parts that make it up.
– The difference in mass is converted into released energy.
• This only happens in the sun and starts
Fission up Close
• An incident neutron causes a large unstable
element to split into smaller elements.
• When the element splits, some of the energy used
to hold the large nucleus is released.
• This happens in nuclear reactors around the world.
E=mc2
1. Which particle would generate the greatest amount
of energy if its entire mass were converted into
energy? EXPLAIN
– electron
– proton
– alpha particle
– Neutron
2. If a proton was completely turned into energy, how
much energy would be released?
Isotopes
Same element (same number of protons)
Different masses (different numbers of neutrons)
- Can be separated by using a mass spectrometer
Mass (u)
Mass Defect
• The mass of the individual protons and neutrons that make up an
element is larger than the actual mass of the element.
• This ‘mass defect’ is converted into the energy needed to hold the
nucleus together.
If the actual mass of the Lithium atom is 6.941u,
-What is the mass defect in u
-What is the binding energy in MeV?
-What is the binding energy in Joules?
Knowledge Test
• How much energy would be released if an
average high school student was vaporized into
energy?
• A hydrogen bomb produces energy when a
diatomic hydrogen element (2p) is split into two
individual hydrogen atoms. A diatomic hydrogen
nucleus has a mass of 2.009u and proton has a
mass of 1.00794u. How much energy is produced
when one single atom is split?
– In MeV
– In Joules