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 If light was a particle (think painted tennis balls)… what pattern would you see on the wall? expectations If light was a wave (think water)… what pattern would you see 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 wave (think water)… How would the energy of a ocean wave (amplitude) affect the speed at which the electrons get kicked out? If light was a particle (think painted tennis balls)… How would the cartoon get more electrons to fly of the metal?

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= 6.63x Js Planck’s constant is modern physics’ version of the penny The energy of a photon is determined by its frequency (and wavelength)

Units A joule is a large unit of energy. When you are talking about small electron, we use an electron volt instead 1eV=1.6x J Ex1. A photon has 3.5eV of energy. How many Joules of energy is that? Ex2. A photon has 4.8x J of energy, how many electron volts is that?

Examples 1.A photon of light has a frequency of 2.5x10 14 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.

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 Absorption Spectrum

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)

F A BC D EG

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.A baryon with a +1 charge 2.A baryon with a -2 charge 3.A meson with a neutral charge 4.A meson with a -1 charge 5.A baryon with a +3 charge 6.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 NameRelative Strength Force RangeForce acts on Strong Force Weak Force Electro-magnetic Force Gravitational Force Very Short Infinite Infinite Nucleons quarks Charges Mass

Creating Nuclear Energy Mass or energy can never be created or destroyed, only converted from one to the other! 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=mc 2 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! Fusion Two smaller elements (anything below iron) fuse together to create a larger element. This is favored by nature because this process releases energy. 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=mc 2 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 u. How much energy is produced when one single atom is split? – In MeV – In Joules