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Thermal Energy; Nuclear Energy; Modern Physics

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1 Thermal Energy; Nuclear Energy; Modern Physics
Unit Fifteen Thermal Energy; Nuclear Energy; Modern Physics

2 Unit Fifteen: Thermal Energy
1. Temperature is the quantity that tells how hot or cold something is compared to a standard. It’s also the measure of the average internal kinetic energy of its particles. A. The kinetic theory of matter states that, if you increase something’s temperature, its matter expands because the molecules move faster. If you decrease its temperature, its matter contracts (shrinks) because the molecules move slower.

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2. At the temperature of absolute zero, there is no molecular motion and no heat in the substance. A. Absolute zero occurs when all atomic and molecular motion stops. This is the lowest temperature possible. B. Absolute zero occurs at 0 Kelvin, or – o Celsius or at – 460o Fahrenheit.

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oF oC K Water Boils Room Temp Water Freezes Absolute Zero – –

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3. Heat and temperature are two concepts that are often confused. They’re related to each other because they are both related to the concept of thermal energy.

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A. Heat is the thermal energy transfer from one object to another because of a temperature difference between these objects. B. Matter doesn’t contain heat. Matter contains thermal energy. Heat is energy in transit.

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C. Heat may be defined as energy that travels from a high temperature object to a lower temperature object. D. Heat is a flow of thermal energy, it is not a substance (matter) that flows.

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E. A material doesn’t possess heat. The appropriate term for the microscopic energy in an object is its internal (thermal) energy. F. A material’s internal (thermal) energy is the total energy of the particles (including their kinetic energy and their potential energy) in the material.

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Thermal equilibrium is reached when two or more objects in contact with each other reach the same temperature. Heat no longer flows between the objects because there is no temperature difference between them.

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Phase Changes / Changes of State Phase Change Description Solid to Liquid Melting Liquid to Solid Freezing Liquid to Gas Boiling Gas to Liquid Condensation Solid to Gas Sublimation Gas to Solid Deposition

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In the previous slide, when water moves from the bottom of the graph to the top of the graph (gets warmer), it gains energy in the form of heat (calories) from the surrounding environment. When water moves from the top of the graph to the bottom of the graph (gets cooler), it loses energy in the form of heat (calories) to the surrounding environment.

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The transfer of thermal energy from one material to another can occur in three ways. 1. By conduction 2. By convection 3. By radiation

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1. Conduction is the transfer of thermal energy in the form of heat from one substance to another or from one part of a substance to another part of the same substance by direct contact. A. This form of transfer occurs most often in solids (i. e. a metal spoon gets hot when left in a pot of boiling water). B. The kinetic energy is transferred from one particle to another when the particles collide.

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C. A wooden or plastic spoon would be an example of a poor conductor or an insulator. D. An insulator delays the transfer of heat. i. Some examples of insulators are wood, wool, straw, and paper. E. A poor conductor is a good insulator and vice versa.

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2. Convection is the transfer of thermal energy by the actual mass movement of heated particles. A. Convection only occurs in fluids (liquids and gases). B. The molecules in a gas are far apart because the bonds holding them together are weak. For this reason, a small energy input results in large movement.

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Boiling pots of water and lava lamps provide graphic illustrations of convection. They are an excellent reminder of the process that drives the movements of the ocean currents and the movements of the atmospheric winds.

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3. Thermal energy transferred by radiation occurs through space in the form of electromagnetic waves. A. Some examples are solar energy, light, radio waves, microwaves

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Conduction, convection, and radiation all occur together in everyday life.

20 Unit Fifteen: Nuclear Energy
The Structure of Matter 1. The smallest divisible portion of matter is the atom. 2. Atoms are made up of electrons, protons, and neutrons. 3. Protons and neutrons lie in the nucleus of the atom and electrons move around the nucleus of the atom. 4. Protons are positively charged (+), electrons are negatively charged (-), and neutrons have no charge (neutral).

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Particle Mass Charge Electron x kg - 1 Proton x kg + 1 Neutron x kg 0

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23 Unit Fifteen: Nuclear Energy
Because the parts of an atom are so small and electrons revolve around the nucleus of atoms, we can not be sure of an electron’s exact location at an exact time like we can for larger objects like a baseball. This principle for very tiny particles is called The Uncertainty Principle and it states that it’s impossible to measure the exact location of a particle at a certain time without altering its momentum and vice versa.

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Since it’s impossible to know a particle’s momentum and position at the exact same time, we say that electrons form a cloud around the nucleus. All this means is that the electron is probably in a certain location around the nucleus.

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5. The atomic number of an atom is the number of protons in its nucleus. A. The properties of an element are defined by its atomic number. B. The atomic number also represents number of electrons in a neutral atom. 6. The mass number of an atom is the the total number of protons plus neutrons in the nucleus.

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7. Isotopes are atoms of the same element (with the same number of protons) but with different numbers of neutrons. A. Examples: carbon – 12 (6 protons, 6 electrons, 6 neutrons) carbon – 14 (6 protons, 6 electrons, 8 neutrons)

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8. Two forces that act on subatomic particles (protons, neutrons, and electrons) A. The electrical force is an attractive force that acts between the electrons around the nucleus and the protons in the nucleus. Positively (+) charged protons attract negatively (–) charged electrons. B. The strong nuclear force is an attractive force that only works with protons and neutrons. It only works when they are very close together in the nucleus of atoms.

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9. On the Periodic Table, the smaller elements (near the top) have about the same number of protons and neutrons (about a 1:1 ratio). They tend to be stable. The larger elements (near the bottom) have more neutrons than protons (about a 1.5:1 ratio). They tend to be unstable (too many unstable neutrons). 10. These large, unstable elements undergo a natural process called radioactive decay so they can become more stable.

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11. A nuclear reaction (involving the atom’s nucleus, not just its electrons as in a chemical reaction) results when an unstable nucleus breaks down and emits radioactive particles in its natural attempt to become more stable.

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12. There are three types of particles / rays released during radioactive decay. A. alpha particle (α) i. helium nucleus (+ 2 charge) ii. largest, slowest, least penetrating particle; stopped by a few sheets of thin paper iii. released during alpha decay

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B. beta particle (β) i. fast moving electron (– 1 charge) ii. smaller and more penetrating than alpha particle; stopped by several sheets of aluminum foil iii. released during beta decay

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C. gamma radiation (γ) i. no particle, no mass or charge, only high energy electromagnetic energy ii. most penetrating and most damaging; stopped by lead iii. always released during radioactive decay of any kind

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13. The half life of a radioactive isotope is the time it takes for one half of the isotope to decay (change from one element into a more stable element). A. Example: The half life of mercury is 31 hours. If you start with 20 g of mercury - 195, how much will be left after 31 hours? (10 g) How much will be left after 62 hours? (5 g)

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When an alpha particle (α) is emitted from a radioactive element, the element’s mass number decreases by 4 and its atomic number decreases by 2 as shown in the equation below. 226 88 4 2 222 86 Ra → He + Rn

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When a beta particle (β) is emitted from a radioactive element, the element’s mass number remains unchanged and its atomic number increases by 1 as shown in the equation below. 209 82 – 1 209 83 Pb → e + Bi The neutron turns into a proton and an electron.

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When a gamma ray (γ) is emitted from a nuclear reaction, the mass number and atomic number of the involved nucleus remain unchanged since gamma rays are pure energy and have no mass.

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Nuclear Fission is the splitting of large unstable (usually uranium) nuclei resulting in a tremendous release of energy. Nuclear Fusion is the combining of small nuclei resulting in an even greater release of energy. The sun uses nuclear fusion to produce energy. 1. With nuclear fusion, 2 hydrogen atoms combine to form 1 helium atom.

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A nuclear fission power plant uses a controlled nuclear fission reaction to boil (superheat) water. This steam is then used to turn a turbine that is connected to a generator. This generator converts the mechanical energy of the turbine into electrical energy. This electrical energy is then sent out to its customers.

42 Unit Fifteen: Modern Physics
There are several oddities about light that we will discuss in this last section of the course. 1. One is that light has both particle-like properties and wave-like properties. 2. Another is that the speed of light is constant in a vacuum. We will discuss the particle and wave properties of light first.

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One of the ways light exhibits wave-like properties is its ability to show constructive and destructive interference patterns. We know that waves of any kind exhibit interference patterns. A. Double slit interference occurs when light of one frequency (one color) is shown through two narrow, closely spaced slits. When this is done, light (constructive – crest to crest interference) and dark (destructive – crest to trough interference) bands will appear on a screen.

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Double slit interference is shown here. This shows the wave-like properties of light.

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2. One of the ways light shows particle-like properties is by the photoelectric effect. This occurs with the ejection of electrons from certain photosensitive metals when light falls upon them. A. The photoelectric effect suggests that light travels as a wave but it interacts with matter as a stream of particles (photons). B. Photons are discrete little bundles of light energy.

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The Photoelectric Effect is shown here. This shows the particle-like properties of light. light rays electrons photosensitive metal

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Remember from the beginning of the semester, that all motion is relative. Motion depends on your frame of reference. For example, if a baseball is thrown at 60 mph at you from a stationary truck, the baseball will be traveling at 60 mph when you catch it. If the truck is moving toward you at 40 mph when the baseball is thrown at you at 60 mph, the baseball will be traveling at 100 mph when you catch it.

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Similarly, if the truck is moving away from you at 40 mph when the baseball is thrown toward you at 60 mph, the baseball will be traveling at 20 mph when you catch it. The baseball has three different speeds depending on the frame of reference.

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Another oddity of light, as mentioned above, is that, no matter what your relative motion is to a light source (approaching it or moving away from it), the speed of light always remains constant in a vacuum.

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People think of space and time as two separate quantities. Albert Einstein thought of space and time as linked together, or as two parts of one whole, called space-time. 1. He surmised that space and time do not exist outside the universe. Space and time only exist within the universe. 2. He also surmised that space and time are linked together by the speed of light, since the speed of light is always constant.

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2. To understand this, instead of thinking as though you are moving through time or moving through space, think of moving through a combination of space-time. A. When you stand still, you are only moving through time and not through space. B. When you move a little, you are moving a little bit through space, but you are still mostly moving through time.

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C. However, when you are moving at the speed of light, you are traveling completely through space and not through time. Therefore, light is timeless and if you were traveling at the speed of light, you would experience no forward motion of time. D. Therefore, time slows down for you as you approach the speed of light. E. In summary, time slows down as you approach the speed of light.

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Since space and time are linked as discussed above, not only does time change as you approach the speed of light, but space also changes as you approach the speed of light. 1. When an object approaches the speed of light, its length contracts along the direction of its motion.

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1. There are some very large objects in the universe, such as large stars, that have very large forces of gravity. These forces of gravity can be so large that they can even bend nearby light rays toward them.

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2. A black hole is the result of a very large star that collapses onto itself. When this occurs, gravity pulls its immense mass together to the point that it becomes almost infinitely dense. With this immense density, the gravity field of the black hole becomes so strong that nothing nearby can escape it – not even light. This is the reason why we can’t see black holes. We only see the effects of black holes on the surrounding environment.

56 The End

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