Presentation on theme: "Thermal Energy; Nuclear Energy; Modern Physics"— Presentation transcript:
1Thermal Energy; Nuclear Energy; Modern Physics Unit FifteenThermal Energy;Nuclear Energy;Modern Physics
2Unit Fifteen: Thermal Energy 1. Temperature is the quantity that tells howhot or cold something is compared to astandard. It’s also the measure of theaverage internal kinetic energy of itsparticles.A. The kinetic theory of matter states that,if you increase something’s temperature,its matter expands because the moleculesmove faster. If you decrease itstemperature, its matter contracts (shrinks)because the molecules move slower.
3Unit Fifteen: Thermal Energy 2. At the temperature of absolute zero, there isno molecular motion and no heat in thesubstance.A. Absolute zero occurs when all atomic andmolecular motion stops. This is thelowest temperature possible.B. Absolute zero occurs at 0 Kelvin, or– o Celsius or at – 460o Fahrenheit.
4Unit Fifteen: Thermal Energy oF oC KWater BoilsRoom TempWater FreezesAbsolute Zero – –
5Unit Fifteen: Thermal Energy 3. Heat and temperatureare two concepts thatare often confused.They’re related to eachother because they areboth related to theconcept of thermalenergy.
6Unit Fifteen: Thermal Energy A. Heat is the thermal energy transfer fromone object to another because of atemperature difference between theseobjects.B. Matter doesn’t contain heat. Mattercontains thermal energy. Heat is energyin transit.
7Unit Fifteen: Thermal Energy C. Heat may be defined as energy thattravels from a high temperature objectto a lower temperature object.D. Heat is a flow of thermal energy, it is not asubstance (matter) that flows.
8Unit Fifteen: Thermal Energy E. A material doesn’t possess heat. Theappropriate term for the microscopicenergy in an object is its internal(thermal) energy.F. A material’s internal (thermal) energy isthe total energy of the particles (includingtheir kinetic energy and their potentialenergy) in the material.
9Unit Fifteen: Thermal Energy Thermal equilibrium is reached when two ormore objects in contact with each other reachthe same temperature. Heat no longer flowsbetween the objects because there is notemperature difference between them.
10Unit Fifteen: Thermal Energy Phase Changes / Changes of StatePhase Change DescriptionSolid to Liquid MeltingLiquid to Solid FreezingLiquid to Gas BoilingGas to Liquid CondensationSolid to Gas SublimationGas to Solid Deposition
12Unit Fifteen: Thermal Energy In the previous slide, when water moves fromthe bottom of the graph to the top of the graph(gets warmer), it gains energy in the form ofheat (calories) from the surroundingenvironment.When water moves from the top of the graphto the bottom of the graph (gets cooler), itloses energy in the form of heat (calories) tothe surrounding environment.
13Unit Fifteen: Thermal Energy The transfer of thermal energy from onematerial to another can occur in three ways.1. By conduction2. By convection3. By radiation
14Unit Fifteen: Thermal Energy 1. Conduction is the transfer of thermal energyin the form of heat from one substance toanother or from one part of a substance toanother part of the same substance bydirect contact.A. This form of transfer occurs most oftenin solids (i. e. a metal spoon gets hotwhen left in a pot of boiling water).B. The kinetic energy is transferred from oneparticle to another when the particlescollide.
15Unit Fifteen: Thermal Energy C. A wooden or plastic spoon would be anexample of a poor conductor or aninsulator.D. An insulator delays the transfer of heat.i. Some examples of insulators arewood, wool, straw, and paper.E. A poor conductor is a good insulator andvice versa.
16Unit Fifteen: Thermal Energy 2. Convection is the transfer of thermal energyby the actual mass movement of heatedparticles.A. Convection only occurs in fluids(liquids and gases).B. The molecules in a gas are far apartbecause the bonds holding them togetherare weak. For this reason, a small energyinput results in large movement.
17Unit Fifteen: Thermal Energy Boiling pots of water and lava lamps providegraphic illustrations of convection. They are anexcellent reminder of the process that drives themovements of the ocean currents and themovements of the atmospheric winds.
18Unit Fifteen: Thermal Energy 3. Thermal energy transferred by radiationoccurs through space in the form ofelectromagnetic waves.A. Some examples are solar energy, light,radio waves, microwaves
19Unit Fifteen: Thermal Energy Conduction, convection, and radiation all occurtogether in everyday life.
20Unit Fifteen: Nuclear Energy The Structure of Matter1. The smallest divisible portion of matter is theatom.2. Atoms are made up of electrons, protons,and neutrons.3. Protons and neutrons lie in the nucleus ofthe atom and electrons move around thenucleus of the atom.4. Protons are positively charged (+), electronsare negatively charged (-), and neutronshave no charge (neutral).
21Unit Fifteen: Nuclear Energy Particle Mass ChargeElectron x kg - 1Proton x kg + 1Neutron x kg 0
23Unit Fifteen: Nuclear Energy Because the parts of an atom are so small andelectrons revolve around the nucleus of atoms,we can not be sure of an electron’s exactlocation at an exact time like we can for largerobjects like a baseball. This principle for verytiny 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.
24Unit Fifteen: Nuclear Energy 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 isprobably in a certain location around the nucleus.
26Unit Fifteen: Nuclear Energy 5. The atomic number of an atom is thenumber of protons in its nucleus.A. The properties of an element aredefined by its atomic number.B. The atomic number also representsnumber of electrons in a neutral atom.6. The mass number of an atom is the the totalnumber of protons plus neutrons in thenucleus.
28Unit Fifteen: Nuclear Energy 7. Isotopes are atoms of the same element(with the same number of protons) but withdifferent numbers of neutrons.A. Examples:carbon – 12(6 protons, 6 electrons, 6 neutrons)carbon – 14(6 protons, 6 electrons, 8 neutrons)
29Unit Fifteen: Nuclear Energy 8. Two forces that act on subatomic particles(protons, neutrons, and electrons)A. The electrical force is an attractive forcethat acts between the electrons aroundthe nucleus and the protons in thenucleus. Positively (+) charged protonsattract negatively (–) charged electrons.B. The strong nuclear force is an attractiveforce that only works with protons andneutrons. It only works when they arevery close together in the nucleus ofatoms.
30Unit Fifteen: Nuclear Energy 9. On the Periodic Table, the smallerelements (near the top) have about thesame 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 a1.5:1 ratio). They tend to be unstable (toomany unstable neutrons).10. These large, unstable elements undergo anatural process called radioactive decayso they can become more stable.
32Unit Fifteen: Nuclear Energy 11. A nuclear reaction (involving the atom’snucleus, not just its electrons as in achemical reaction) results when an unstablenucleus breaks down and emits radioactiveparticles in its natural attempt to becomemore stable.
33Unit Fifteen: Nuclear Energy 12. There are three types of particles / raysreleased during radioactive decay.A. alpha particle (α)i. helium nucleus (+ 2 charge)ii. largest, slowest, least penetratingparticle; stopped by a few sheets ofthin paperiii. released during alpha decay
34Unit Fifteen: Nuclear Energy B. beta particle (β)i. fast moving electron (– 1 charge)ii. smaller and more penetrating thanalpha particle; stopped by severalsheets of aluminum foiliii. released during beta decay
35Unit Fifteen: Nuclear Energy C. gamma radiation (γ)i. no particle, no mass or charge, onlyhigh energy electromagnetic energyii. most penetrating and most damaging;stopped by leadiii. always released during radioactivedecay of any kind
36Unit Fifteen: Nuclear Energy 13. The half life of a radioactive isotope is thetime it takes for one half of the isotope todecay (change from one element into amore stable element).A. Example: The half life of mercury is31 hours. If you start with 20 g ofmercury - 195, how much will be left after31 hours? (10 g) How much will be leftafter 62 hours? (5 g)
37Unit Fifteen: Nuclear Energy 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.226884222286Ra →He +Rn
38Unit Fifteen: Nuclear Energy 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.20982– 120983Pb →e +BiThe neutron turns into a proton and an electron.
39Unit Fifteen: Nuclear Energy When a gamma ray (γ) is emitted from anuclear reaction, the mass number and atomicnumber of the involved nucleus remainunchanged since gamma rays are pure energyand have no mass.
40Unit Fifteen: Nuclear Energy Nuclear Fission is the splitting of largeunstable (usually uranium) nuclei resulting in atremendous release of energy.Nuclear Fusion is the combining of smallnuclei resulting in an even greater release ofenergy. The sun uses nuclear fusion toproduce energy.1. With nuclear fusion, 2 hydrogen atomscombine to form 1 helium atom.
41Unit Fifteen: Nuclear Energy A nuclear fission power plant uses acontrolled nuclear fission reaction to boil(superheat) water. This steam is then used toturn 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.
42Unit Fifteen: Modern Physics There are several oddities about light that wewill discuss in this last section of the course.1. One is that light has both particle-likeproperties and wave-like properties.2. Another is that the speed of light isconstant in a vacuum.We will discuss the particle and wave properties of light first.
43Unit Fifteen: Modern Physics 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 whenlight of one frequency (one color) is shownthrough 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.
44Unit Fifteen: Modern Physics Double slit interference is shown here. Thisshows the wave-like properties of light.
45Unit Fifteen: Modern Physics 2. One of the ways light shows particle-likeproperties is by the photoelectric effect.This occurs with the ejection of electronsfrom certain photosensitive metals whenlight falls upon them.A. The photoelectric effect suggests thatlight travels as a wave but it interactswith matter as a stream of particles(photons).B. Photons are discrete little bundles of lightenergy.
46Unit Fifteen: Modern Physics The Photoelectric Effect is shown here. Thisshows the particle-like properties of light.light rayselectronsphotosensitive metal
47Unit Fifteen: Modern Physics Remember from the beginning of the semester,that all motion is relative. Motion depends onyour frame of reference. For example, if abaseball is thrown at 60 mph at you from astationary truck, the baseball will be traveling at60 mph when you catch it. If the truck is movingtoward you at 40 mph when the baseball isthrown at you at 60 mph, the baseball will betraveling at 100 mph when you catch it.
48Unit Fifteen: Modern Physics 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 at20 mph when you catch it. The baseball hasthree different speeds depending on the frameof reference.
49Unit Fifteen: Modern Physics Another oddity of light, as mentioned above,is that, no matter what your relative motion isto a light source (approaching it or movingaway from it), the speed of light alwaysremains constant in a vacuum.
50Unit Fifteen: Modern Physics People think of space and time as two separatequantities. 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 existoutside the universe. Space and time onlyexist within the universe.2. He also surmised that space and time arelinked together by the speed of light,since the speed of light is alwaysconstant.
51Unit Fifteen: Modern Physics 2. To understand this, instead of thinking asthough you are moving through time ormoving through space, think of movingthrough a combination of space-time.A. When you stand still, you are onlymoving through time and not throughspace.B. When you move a little, you are moving alittle bit through space, but you are stillmostly moving through time.
52Unit Fifteen: Modern Physics C. However, when you are moving at thespeed of light, you are traveling completelythrough space and not through time.Therefore, light is timeless and if youwere traveling at the speed of light, youwould experience no forward motion oftime.D. Therefore, time slows down for you asyou approach the speed of light.E. In summary, time slows down as youapproach the speed of light.
53Unit Fifteen: Modern Physics 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 oflight, its length contracts along thedirection of its motion.
54Unit Fifteen: Modern Physics 1. There are some very large objects in theuniverse, such as large stars, that have verylarge forces of gravity. These forces ofgravity can be so large that they can evenbend nearby light rays toward them.
55Unit Fifteen: Modern Physics 2. A black hole is the result of a very large starthat collapses onto itself. When this occurs,gravity pulls its immense mass together tothe point that it becomes almost infinitelydense. With this immense density, thegravity field of the black hole becomes sostrong that nothing nearby can escape it– not even light. This is the reason why wecan’t see black holes. We only see theeffects of black holes on the surroundingenvironment.