Intro Physics Surv
Intro Physics Surv PHYS 1030
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This 58 page Class Notes was uploaded by Iva Cormier on Sunday October 11, 2015. The Class Notes belongs to PHYS 1030 at East Tennessee State University taught by Brian Espino in Fall. Since its upload, it has received 39 views. For similar materials see /class/221406/phys-1030-east-tennessee-state-university in Physics 2 at East Tennessee State University.
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Date Created: 10/11/15
Chapter 2 The nature of things The Greeks thought about the nature of matter Matter can be described as the substance of which physical materials are composed of Examples of material substances such as wood ice water sausage gold All of these are composed of matter What do different types of substances have in common with each other One idea is that all matter can be divided up into smaller pieces Do this enough and eventually you would get to pieces so small they are no divisible The Greeks called these particles atoms Any process that changes a substance into other simpler substances is called chemical decomposition An example is if you pass electricity through water you can split up the water into hydrogen and oxygen Some substances cannot be further decomposed into simpler substances The are called elements Examples are hydrogen oxygen carbon gold It turns out that each element is made up one only one kind of atom Different elements have different types of atoms Hydrogen is made of hydrogen atoms gold is made of gold atoms An atom is defined as the smallest particles of a chemical element Each type of atoms is characterized by what is called the atomic number for that element VVater Water is made up of hydrogen and oxygen so water cannot be an element Substances made up of more than one element are called chemical compounds Water H20 Salt NaCl Chemical compounds can be split up into smaller and smaller pieces The smallest particles of a compound that still retains the properties of the compound is called a molecule Some elements are made up of two atom molecules For example hydrogen gas is made up of two hydrogen atoms hydrogen gas H2 This is called a diatomic molecule Quantitative measurement using numbers to describe situation Car drives 100 mph It s lOOOF outside Qualitative description without numbers The car is fast It s hot Macroscopi phenomena that can be easily observed Occurs on a large scale Temperature is macroscopic When you smell something a macroscopic observation occurs Microscopic occurs on a very small scale An unseen level for humans The speed of the individual atoms that results in the given temperature is microscopic The atoms that produce the smell can be studied microscopically States of matter solid has fixed shape fixed volume molecules are close to together and locked in fixed arrangement hardest to compress liquid has fixed volume does not have a fixed shape Think about pouring water into different shaped cups Molecules are close to together but not rigidly fixed to each other hard to compress gas no fixed shape no fixed volume gas expands to fill the container it is in molecules are relatively far away Gases can be compressed How do we know atoms exist ifthey re so small We can detect there presence by using tools which employ the rules of physics We can t see electrons but when electrons hit a fluorescing screen it lights up Also we can detect forces from individual atoms atomic force micrsopy Section on making estimates It can be useful to learn how to make wise estimates to find an approximate answer to many questions This is useful when no calculator is handy or you really don t care about the exact amount Estimations and order of magnitude calculations Estimate the number of people needed to make human chain across Tennessee TN is about 500 miles long 1 mile about 16 km So TN is about 800 km long Reach of a person is about 1 meter 800km is 800 1000 meters You would need about 800 000 people Atomic models Greek model atoms was an unchanging atom like a tiny solid ball Some experiments disproved this idea Planetary model electrons orbit around a central nucleus made up of protons and neutrons In the 1920 s new experiments involving electrons contradicted this idea Quantum theory of the atom So far has not been disproved We will discuss this much later Chemical reaction Any rearrangement of molecules to produce different molecules is called a chemical reaction example burning respiration photosynthesis Conservation of matter during any chemical reaction the total number of each type of atoms must stay constant C02 gtC02 example burning methane gas CH402 gtC02H20 In this reaction the number of each atom types is not balanced Chemical reactions need to be balanced that way the conservation of matter rule is held true CH4 202 gt C02 2H20 Now the are equal numbers of each type of atom on both sides of the equation Quantum physics Comes from idea that physical quantities are discontinuous or quantized Examples charge comes in quantities of 16x1039l9 C All electric charges are some integer multiples of 16x1039l9 C Let s call 16x10 19C e Allowed charges are 16x103919C 32x103919C 48x103919C or 1e 2e 3e 4e Cannot have 15e or 21x103919C More examples of quantization Light occurs is packets called photons lfyou dimmed a light bulb enough you could release light 1 photon at a time Photons will be further discussed later Electrons that orbit the nucleus have discrete quantized energies The Waviness of matter Louis de Broglie thought that radiation such as light could behave as a wave and as a particle then particles should behave like waves Came up with a formula to predict the wavelength of a material particle wavelength of particle hmassvelocity Wavelength of a 1 kg ball rolling 1 ms 66x10 34Jls 1kg1mS This number is very small Too small to detect 2 66x10 34m Wavelength of an electron moving with a typical velocity of 107 m s 66x1034J S 91x10 31kgx107ms Still very small About 110 the size of an atom Can be detected by very careful experiments 7x10 11m For big objects anything of noticeable size the wavelength of the object is amazineg small The object needs to be very small for its wavelength to be detectable Quantum physics is more useful at the microscopic level Quantum mechanics accurately describes the behavior of particles such as electrons and atoms For larger objects such as people the quantum mechanics breaks down to classical mechanics The rules of physics that we re use to using Turns out that energy in an electricmagnetic field does not come in a continuous values It is quantized EM fields that oscillate produce light waves The energy in these waves is quantized The amount of energy in the field can only have certain values These energy values are O hf 2hf 3hf 4hf h Planck s constant 66x103934 Js f is the frequency Remember that vf9t or f cX Thus the values of energy can be written as O h cQc 2hct 3hCgtL 4hc9t Photons are the quanta carriers ofthe quantized energy The photon will have an amount of energy of Planck s constant times the frequency ofthe photon E hf Different colors have different wavelengths Wavelength is related to frequency by f ck or 9tcf So different colors have photons of different energies Photons only exist at the instant of impact between light and an object When a photon hits a screen and causes it to light up the entire EM field loses an amount of energy equal to the energy ofthe photon This is how light interacts with matter Light a wave sometimes interacts with matter like a particle To explain how Electromagnetic waves light are produced we first discuss the electron Quantum theory of the atom describes the behavior of electrons Electrons can described to follow the rules of standing waves Show standing waves with long spring Notice the number of loopnodeshumps are quantized This means the wavelength and frequencies are quantized Thus the energies of the electrons are guantized The more loops that are present the lower the wavelength or higher the frequency This means higher energy Electron waves are similar but bent into a circle See pictures on page 342 343 Each frequency corresponds to a quantum state The quantum states have their own energy level The lowest energy level is called the ground state Higher energy levels are excited states They are more energetic than the ground state Energy level diagram Shows the quantized energy levels that the electrons are allowed to exist in This will be determined by the type of atom NS N4 l l l l 3 l l l l N2 l l l mug in l vu miuiglul l l l l l l l l l l l l sums I lulmvlnlnll Nl The energy of the electrons is quantized For an electron to change energies it must jump from one state to another Emission When an electron falls from a higher level to a lower level a photon is emitted The photon will have energy equal to the difference in the quantum jump The atom gives off light The change in the energy levels is equal to the energy of the photon is E hf note quite often we use a new energy unit called the electronvolt eV It s more convenient than the Joule because the energies dealt with are small Absorption Atoms can absorb light photons If a photon hits an atom and it s energy matches the change in energy between electron energy levels the photon is captured by the atom To quotmake room for the energy and electron is bumped up to a higher level This process is the opposite of emission Since the energy levels that the electrons can occupy are quantized it means that only certain frequency photons can be emitted or absorbed The energy levels depend on the atom So different atoms emitabsorb different colored photons different wavelengths spectroscopy by looking to see the wavelengths ofthe emittedabsorbed photons you can determine what material is made out of Knowledge about atomic spectra can be very useful in some situations By looking at the radiation of a distant star you can determine what gases are in the star Or let s pretend you want to have a light source that produces only specific colors You can decide what type of gas lamp to use This is also related to making lasers By exciting electrons to different energy levels we can make lasers that produce different colors Spectrum spectrum set of frequencies that are emittedabsorbed White light has a continuous spectrum White light is made up of all the colors line spectrum produced when only precise separated frequencies are emitted Two types Emission spectrum shows the wavelengths that are emitted in form of lines on the spectrum Absorption spectrum shows the wavelengths of the photons that are absorbed as gaps in a continuous spectrum httpwwwcoloradoeduphvsicsZOOOquantumzonein dexhtml If we make an energy level diagram we can see the corresponding sprectrum httpphyseducksueduvqmfreethpecht ml Uncertainty Principle When doing quantum physics we deal with probabilities Examples what is the probability that an electron has so much velocity The probability that the electron is a certain distance from the nucleus For certain pairs of variables one example is position and velocity the uncertainties for the variables are related The product of the uncertainties is approximately equal to hm h Planck s Constant 66x103934J s AXAv hm If the spread in one of the variables goes down the spread in the other goes up If you know one variable exactly the other variable can be anything PE Potential Energy Curve total energy Classically classically classically allowed forbidden forbidden region region region position Potential energy curve Classical particles can t go to regions where the potential energy is more than the total energy Quantum mechanics says otherwise That there is a probability that the particle can be in a restricted region When a particle passes through the classically forbidden domain it is said to have tunneled through a barrier Example An electron or other tiny particle is allowed to tunnel through a barrier via quantum mechanics There is a probability the particle can pass through a wall People are made up ofthe same tiny particles However the probability that a person can pass through a wall practically nonexistent Here we can see that quantum mechanics shows that there is a probability that a particle can be where classical physics says it s forbidden Setting up a barrier we can see quantum tunneling go to tab 1 15 The graph represents the probability that the particle is at that location httpwwwquantum physicspolytechniquefr The height of the graph at each position is related to the probability that the particle is located at that position Wave behavior of particles Earlier we mentioned how particles can be described as waves Here is some evidence that particles behave like waves By passing particles through a single slit we can observe a diffraction pattern Diffraction is how waves behave when they bend around corners and spread out through gaps Double slit experiment shows that two sources of particles for example photons interfere with each other Interference is a wave propertv httpphvseducksueduvqmindexhtml Use single and double slit simulators to see wave nature of particles Radiation The unit of biological damage by ionizing radiation is called the rem The number of rems is a direct measure of how many cells were damaged Radiation sickness damage to the red blood forming cells of the bone marrow and to the cells in the intestinal lining Whole body versus partial body radiation The body can tolerate large doses to non vital parts hand or foot If a large amount of radiation hits your foot you may lose the foot but not get radiation sickness NRC has a occupational dose limit of 5 remyear and no more than 10 rem5 years These are sudden whole body doses A sudden dose of 25 to 100 rems to the whole body will cause short term changes in the blood that might be noticed 100 300 rems produces typical symptoms of radiation sickness fever vomiting damaged red blood cells reduced white blood cells loss of hair spontaneous bleeding hemorrhages beneath the skin 500 rems produces 50 fatalities 1000 rems death within 30 days 10000 rems death within hours a day or two On the average a person in the US receives about 03 rem 300 mrems of radiation per year Estimate how much radiation you receive in a year httpwwwepagovrpdwebOOunderstandcacuatehtm Putting risks of radiation in perspective Estimated Days of Life Expectancy Lost From Various Risk Factors Smoking 20 cigarettes a day 2370 65 years Overweight by 20 985 27 years Mining and Quarrying 328 Construction 302 Agriculture 277 Government 55 Manufacturing 43 Radiation 340 mremyr for 30 years 49 Radiation 100 mremyr for 70 years 34 List of activities calculated to have a oneinamillion chance of causing death Smoking 14 cigarettes lung cancer Radiation dose of 10 mrem cancer Eating 4O tablespoons of peanut butter liver cancer Eating 100 charcoal broiled steaks cancer Spending 2 days in New York City air pollution Driving 40 miles in a car accident Flying 2500 miles in a jet accident Canoeing for 6 minutes accident How to minimize doses distance keep sources as far as practically possible Hold source with forceps instead of fingers time reduce the time spent near the source of radiation 0 shielding keep a barrier between you and the source Beneficial uses Used as tracers in medicine 14C or 3H can be used to track the movement of food through the body Doctors can place some a small amount of a radioactive isotope in the medicine Then use radiation detectors to track how the medicine spreads throughout the body Chernobyl disaster Many Europeans obtained doses from about 10 millirem about the same as a diagnostic x ray to 1 rem For people closer to the accident dosages were higher Half life describes how long it takes for radioactive isotope to decay How long it remains dangerous The two most harmful isotopes released were iodine and cesium 131i and 137Cs The half life of 131i is only eight days so soon the iodine was at harmless levels The half life of 137Cs is 30 years so it is dangerous for a long time Nuclear Power 1000 MW hydroelectric power plant uses the energy of 60000 tonnes of water every second 1000 MW coal burning plant uses 10000 tonnes of coal each day 1000 MW nuclear power plant uses 100 tonnes of uranium each year Another power comparison Small town can be leveled by millions of tonnes of earth or water in a landslide or flood Same town can be leveled by 1000 tonnes of high explosives in several hundred chemical bombs Hiroshima with a quarter million people was leveled by 1 nuclear bomb with 42 kg of uranium Nuclear fusion the uniting of two nuclei to form a single larger nucleus Nuclear fission the splitting of a single nucleus roughly in half to form two smaller nuclei Suppose you had the hydrogen isotope 2H They are held together by the strong nuclear force Splitting the nucleus into a separate proton and neutron takes energy The separated proton and neutron have more energy than the 2H nucleus the excess energy is a form of nuclear energy Now you put together a neutron and a proton n p gt 2H The left hand side ofthe equation has more energy than the right hand side Energy is conserved so the extra nuclear energy is transformed into thermal energy and radiation Another example is the fusion of two hydrogen nuclei This is how the sun and many other stars get there energy When fusion occurs you add up the number of protons and the number of neutron example When two 3H6 fuse they form an isotope of what element aheium b lithium c beryllium d boron hint use periodic table When He fuses with fBe they create which isotope a 162C b 68C c 142C d 1620 e EN See Nuclear energy curve The lower the energy the more stable the isotope Mass number 56 iron is the most stable For nuclei lighter than iron the fusion results in a reduction of nuclear energy The fusion is self sustaining Nuclear energy transformed to thermal energy For nuclei heavier than iron fusion results in more nuclear energy Such a reaction requires an outside source of thermal energy Thermal energy is converted to nuclear FISSIon Fission occurs when a nucleus splits into two smaller nuclei In this example a neutron is added to a uranium nucleus Fission occurs after neutron is added to an nucleus to make the nucleus unstable The nucleus then splits into two smaller nuclei Remember that large atoms have many more neutrons than protons while smaller atoms have about the same number of neutrons as protons When the large nucleus splits into two smaller nuclei now the small nuclei still have many more neutrons than protons This will release some more neutrons These extra neutrons can available to start fission in other uranium nuclei Thus a chain reaction has started Two isotopes of uranium 235U and 238U When you add a neutron to the two isotopes only the 235U has much chance of fissioning The 238U just absorbs the neutron and becomes 239U A nuclear bomb needs nearly pure 235U to sustain a rapid chain reaction needed to fission a large chunk of uranium If there is a lot of 238U present the chain reaction will fizzle out Natural uranium is less than 1 235U The 235U must be separated from the more than 99 that is 238U This takes a lot of effort It turns out if you add a neutron to 238U a reaction can take place that makes a new element that fissions like 235U This manmade element is plutonium lfthere is not enough 235U only a few fissions will occur Two many ofthe expelled neutrons will miss the other nuclei if the amount is too small Critical mass the mass of an isotope that is needed for a chain reaction to be sustained For 235U the critical mass is 25 kg For 239Pu the critical mass is 8 kg See figure 1619 for ways how to make a mass that is below critical mass past the critical point Fusion Bomb Uses nuclear fusion to release a lot of energy 2H 3H gt 4He n energy 4He n is the result instead of 5He because 5He is very unstable Uses 2H and 3H because the fusion will occur at lower temperatures than 1H and 2H like the fusion inthesun Fission bombs are limited by their size since a mass that is too large would fission spontaneously Fusion bombs have no limit in size since the hydrogen will not explode spontaneously
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