Modern Physics Wave-Particle Duality Model of the atom Radioactivity / Four Forces of nature

Wave-Particle Duality When tested as if it were a wave, light behaves like a wave. Light will: – Diffract – Refract – Exhibit interference – Polarize – exhibit the Doppler effect (ex. Red shift) When tested as a particle, light behaves like a particle (ex. the photoelectric effect).

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Double slit experiment

Photoelectric Effect When a high frequency light falls on a metal surface, the electrons in the surface absorb the light's energy and break free.

Double Slit Experiment

The nucleus of the atom The neutrons and protons are grouped together in the nucleus, which is at the center of the atom. If the atom were the size of your classroom, the nucleus would be the size of a single grain of sand in the center of the room. Most of an atom’s mass is concentrated in the nucleus.

Scientists describe all of nature with only four forces. Gravitational force Weak Nuclear force Electromagnetic force Strong nuclear force It is important to note that scientists do no know why these forces exist or what causes them. We only observe their effects and propose they are there.

Four Fundamental Forces- Bill Nye HYaY HYaY

Every process we know in the universe can be explained in terms of these fundamental forces.

Gravity Weakest of the four forces The force of gravity causes objects to be attracted to each other We learned about gravity when we talked about forces (last semester)! We will talk more about gravity in a couple days

Weak Nuclear Force Causes a neutron to break into a proton and an electron producing a new element Weaker than both the electric force and the strong nuclear force. Causes radioactive decay Only occurs at the subatomic level

Electromagnetic Force The force is the attraction between protons (positive) and electrons (negative). Electrons are bound to the nucleus by electromagnetic forces.

Strong Nuclear Force Holds the nucleus of an atom together Attracts neutrons and protons to each other, otherwise the positively charged protons would repel each other.

Marie Curie – Nobel prize winner The word radioactivity was first used by Marie Curie in She used the word radioactivity to describe the property of certain substances to give off invisible “radiations” that could be detected by films.

Radioactive Decay Three different kinds of radiation given off by radioactive materials: – Alpha rays – Beta rays – Gamma rays called “rays” because the radiation carried energy and moved in straight lines, like light rays.

Radioactivity comes from the nucleus of the atom. If the nucleus has too many neutrons, or is unstable the atom undergoes radioactive decay. decay - to "break down."

Atomic Decay Alpha decay: the nucleus ejects two protons and two neutrons. Beta decay: a neutron in the nucleus splits into a proton and an electron. Gamma decay occurs because the nucleus is at too high an energy. The nucleus falls down to a lower energy state and, in the process, emits a high energy photon.

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Radioactive decay gives off energy. The energy comes from the conversion of mass into energy. Because the speed of light (c) is such a large number, a tiny bit of mass generates a huge amount of energy. Radioactivity occurs because everything in nature tends to move toward lower energy.

Radiation The flow of energy through space. Forms of radiation: – Light – Radio – Microwaves – X-rays Many people mistakenly think of radiation as only associated with nuclear reactions.

X-ray machines X-rays are photons Used to produce images of bones and teeth on x-ray film. X-ray film turns black when exposed to x- rays.

X-Rays Uses High level therapeutic x-rays are used to destroy diseased tissue, such as cancer cells. The beams are made to overlap at the place where the doctor wants to destroy diseased cells.

CAT scan Computerized Axial Tomography Produced by a computer that controls an x-ray machine as it takes pictures of the body from different angles. Produces three-dimensional images of bones and other structures within the body.

Radiation Detection The Geiger counter is a type of radiation detector invented to tell when radiation is present and to measure its intensity.

Fission and Fusion Fission/Fusion and Nuclear Reactors- 3:25- 6:40 & 7:30-10:35 ADdg&list=PLD0edOcD4GTQZHO9iVuUyDILzm SygK6At ADdg&list=PLD0edOcD4GTQZHO9iVuUyDILzm SygK6At

Fusion reactions Nuclear reaction that combines, or fuses, two smaller nuclei into a larger nucleus. It is difficult to make fusion reactions occur because positively charged nuclei repel each other.

Fission reactions A fission reaction splits up a large nucleus into smaller pieces. A fission reaction typically happens when a neutron hits a nucleus with enough energy to make the nucleus unstable.

Nuclear Reactions and Energy A nuclear reaction is any process that changes the nucleus of an atom. Radioactive decay is one form of nuclear reaction.

Nuclear Reactions and Energy If you could take apart a nucleus and separate all of its protons and neutrons, the separated protons and neutrons would have more mass than the nucleus did. The mass of a nucleus is reduced by the energy that is released when the nucleus comes together. Nuclear reactions can convert mass into energy.

Both these nuclear reactions release a small portion of the mass as large amounts of energy. Nuclear fusion is what powers a modern nuclear warhead. Nuclear fission (less powerful) occurs in an atomic bomb (like the ones used against Japan in WWII), or in a nuclear power plant. atomic bomb Nuclear Reactions and Energy

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Mass Energy Equivalence The energy released can be calculated using the equation: E = mc 2 Where: E = energy released (J) m = mass difference (kg) c = speed of light in a vacuum (3 x 10 8 m/s) E m c2c2

Practice problem #1 The energy equivalent for a 5.5 x kg mass is:

Practice problem #2 The mass of an object with an energy equivalent of 4.7 x 10 8 J is: