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Basic Physics III Lecture 23
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Title  Basic Physics III Lecture 23 
Title of Series  Basic Physics III 
Part Number  23 
Number of Parts  27 
Author 
Smy, Michael

License 
CC Attribution  ShareAlike 3.0 Unported: You are free to use, adapt and copy, distribute and transmit the work or content in adapted or unchanged form for any legal and noncommercial purpose as long as the work is attributed to the author in the manner specified by the author or licensor and the work or content is shared also in adapted form only under the conditions of this license. 
DOI  10.5446/12959 
Publisher  University of California Irvine (UCI) 
Release Date  2013 
Language  English 
Content Metadata
Subject Area  Physics 
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Transcript
00:05
last lecture we talked about a B atomic spectroscopy and
00:12
there's 1 additional remark I'd like to make by entering this example of inventors have always assumed that for example hydrogen atoms that they are naturally in the ground state and not and some
00:32
excited state and if you have a look at a gas at some tempered energy can be exchanged between Adams and John Adams can acquire more energies on the question is this enough tool actually excite some of these I wouldn't have been on the grounds that we're going to estimate the average kinetic energy of hydrogen atoms ruled temperature and then explained from that estimated y all the high Adams on in the ground state school children therefore a they make no right to do that we need to estimate the average kinetic energy the average kid energy of calmly gas or what so times Boltzmann's constant times temperature and this is the value of the Boltzmann constant 1 . 3 8 times 10 to the minus 20 a fair jewel per cow and this is the tools and then multiplied the the temperature of the pool for example which is approximately 300 calories and if we do that we get an energy about 0 . 0 4 it carnival and this energy is much much smaller than 1st excitation became excited on your 10 from the previous example calculated that it takes 10 . 2 Alec tumbles to get to the 1st excited state and so would require many many air criticisms of hydrogen atoms to build up energy and on tour with from all that is extremely unlikely therefore hydrogen atoms all B in the ground state as long as they are the temperature of costs Arab to increase the temperature by large amounts of this mingle among the way for example for hydrogen gas in the sun before we finish our discussion quantum mechanics 1 important ingredient didn't talk about it fingers uncertainty principle so I you may recall that they talked about means talk about fraction mean that we have a theme that has sectional and an intensity as a function of radius that looks like a ghost function or dysfunction so I really care consider theme position uncertainty full because of the use of the Munger ponds and be position uncertainty the photon at the waste is roughly W as euro prominent divided by and that is because we have this a factor to win him instead of 1 so be aired Yukon strict photons at the waist we know know that photons that have a transfers position that it is within this range of Delta acts as the waste divided by 2 he also noted that he divergent angle for such means is given as Labrador tight times times the race can calculated what transverse momentum uncertainty that know the if the being diverging can no longer assume that awful chance exactly in the same direction and so if you multiply this equation with momentum the product of momentum times divergent angle that gives us the amount of momentum transfers to the propagation direction of use that the momentum as the trunk constant divided by the wavelength then we uncertainty in the in the transverse momentum meaning momentum we are the virgins and its H divided by Iowa W . 8 of a pie to Thailand's H a at another words momentum uncertainty in the transverse direction schools times aged divided by by the way if we then multiply the position uncertainty it corresponding have momentum transverse direction let me get the product of those who is aged this is actually there just 1 example of of uncertainty relations but in any cadre ago any situation the uncertainty in the momentum measurement position is always at least H bond with bigger than also fallout for photons and means we can multiply this violation of the 1st factor with the speed of light and we can divide the 2nd factor by the speed of light and at the same time so far and therefore we get Seaton's Delta P X which is the uncertainty in the energy of top Delta X divided by a which is the uncertainty in the timing of so we get another uncertainty relations that the product of all energy uncertainty in Taiwan's is also at least as big and that is also true fallout for all particles and all situations now that philosophical implications of the quantum theory of quantum mechanics it isn't just that emphasis measurements of uncertainties that trivial back but added that the
06:35
quantities themselves are not defined or don't exist at beyond that uncertainty meaning that it makes no sense at all to talk about the momentum that is more precise than that given continent and that means that quantum theory necessarily probabilistic since it requires both momentum and position determination of infinite position would define the exact trajectory exact rejected these don't exist anymore and can't we can instead it can only define probability is the set up of the experiment that decides how much uncertainty have momentum and how much have position for example my goes in being can have a white than I have a very precise determination of position but I have a precise determination of the transfer since goes things don't exist beyond that limit of uncertainty the way I make my experiment actually defines a physical reality such as interpretation of quantum field many that scientists did not like this this kind of interpretation beneath that reality show existence independent of whether America's on analysis strange consequence of the uncertainty relation that since we have 1 between energy and time that means that we can borrow some energy out of the vacuum of nothing as long as we don't do it for Murdoch if I want to add a great stadium ELECTRONIC positron out of nothing that I need to borrow about what may square that lasts for 1 inning of energy I can do that for each fall over all want time without violating any physics principles and that means that the vacuum is constantly fluctuating meaning that a virtual particles of their produced Out of nothing and disappear again for brief periods of time and you may think that it has no consequence but they are actually measurements that the middle such quantum for which it needs that Syria have position uncertainty 1 willing needle and the corresponding precise determination of momentum it make it doesn't make sense even talking about In quantum theory talking about a position that is more precise and this 1 differ have my in indeed actually is 1 that I have got to responders 1 1 and sign them and there is no more a definition of positions with me that our position is only defined up to the limit on the size of that of this is a chance was uncertainty of the photons traveling and I cannot for this particular mean I cannot talk about position off photons but it's he'll he'll he'll its it it doesn't make sense in terms of on the field of even are talking mob on the photon this year he'll he'll we can only say that it's that it's inside me and similarly given that there is a risk of spread and the directions I cannot talk about the direction of the photon more precisely than orders given by the yet yes there so at that that is the real thing yeah my experimental set up decides precise and Of course there are the uncertainty relations Moreira some some quantities don't exist at all for example in all double slid experiment that it doesn't it the difference between this slipped and doesn't exist at all so light can take past Bullet can shake this past Ontario cannot talk about whether it actually took this time that this but we passed themselves don't exist only a summation of food I'm but I'm sorry say occurred yet if yeah if you locate the that have changed experiment still for example are you can that your kind shine at while you can block 1 of those let's many of located the photon has to go through the other 1 but then you have changed experiment interference pattern will along will be the same there no less than 8 different a philosophical interpretations of how to deal with this Soviet aspect of quantum mechanics including me classical interpretation that reality ought to be independent of measure however we
12:41
can calculate still with the the uncertainty principle of all the font Canucks if we are still there developed from small moves in a straight line with a constant speed of about 1 . 1 times 10 6 meters per 2nd and it has been measured with a precision of 0 . 1 0 % speed them and the question is what is the maximum precision with which Arab position could His simultaneously to answer that 1st expressed their speed and terms the speed of light because it's more convenient so this is actually a 0 . 3 6 7 % of life we know what these the momentum of the garlic from because we simply have multiplied a would ask classically and of relativistically that velocity and you get momentum of 1 . 8 7 barricade Christie's given that know that this momentum measure to 0 . 1 Percent precision so if I multiply this this momentum with 0 . 0 1 or 0 . 1 cent when I get there too High Times out of is this times to try this at this time to hire or 11 . 7 7 from seat finale have momentum uncertainty over times momentum on and I can get position uncertainty by taking the time constant divided by I don't and that gives me 1 . 2 4 from both Michael theaters divided by 11 . 7 7 from bolts or position uncertainty about a 0 . 1 1 might go so that is and I the atomic diameters of relatively small distance but for electron it's actually quite a large just because of the forms typically uncertainty the coming so this is how you would calculated the 3 uncertainty principle let's look at a macroscopic example let's calculate the uncertainty in position imposed by the uncertainty principle on about 150 grams baseball phone that and I sleeve miles per hour with the uncertainty of plus minus 2 miles all we can do it the same way we get get momentum uncertainty richest 2 miles off or 0 . 9 meters per a 2nd times the mass of the baseball and that gives us momentum uncertainty the value of all get a position answer and justice Planck's constant relied hired by this will make demands and we get a summer . 8 times 10 to the minus 34 meters of anybody give the uncertainty principle as an excuse what equipment and hit the ball it's relating excuse a tremendously small number even compared with the size of a atomic Moclips and finally a let's look at the energy time uncertainty relation thrower in the seventies new prodigal was discovered called shape size as on and is a measure of the energy loss of 3 . 1 key policies but that measurement has intrinsic uncertainty of 63 air K script the question is how long does this article in other words the assumption is that the reason why it has intrinsic uncertainty built into its the measurement of the Masters that comes from its finite life so that the energy uncertainties 63 KDD a not without the sees good because energy uncertainty multiplied with 2 Piute amended 396 and their corresponding time uncertainties adult T 1st h divided by 2 high energy and all multiplying with see its 1 . 2 4 Trumbull Michael commuter divided by 396 case he was 3 . 1 3 9 millimetres never want expressed as the time that I need to divide by by the speed of light and I get about 10 to the minus 26 tho the lifetime of this has on 10 to the minus 20 seconds its were a shortlived and that is why it has uncertainty energy or in its must build it really last remark about quantum theory various actually even little I emphasized that electrons electromagnetic waves and behave Aris similar which there is 1 important difference other member of the child of a poet and that is photons and other socalled boat was once an and I like it would they like to be part of the same way for example you can make laser beams all the 4 times a trouble in the same state however are so that kind of social book their electrons on the other hand there called me on this and other such particles and they are not very sociable and in fact not even 2 more there will ever be in the same state so that means in particular for the atom that a to Alec trance can occupied exacts a calmly level with the same angular momentum the and that so if you have complex atoms Oberlin behind that all the Ella Trans can't be sitting in in the ground state variable 1st fill in the ground state of Ohio State's and so on and that is important and our understanding history so that when I'll summarize quantum mechanics so we started trunks hypothesis explaining the black body radiation spectrum and assumption laws that molecule of vibration energy is quantized of each with is the frequency in ages plants constant and from that Einstein suggested the particle of flight where the particle flight is called photon it has energy H F and momentum rage over land and this not only explains plants hypothesis but also leave photoelectric effect the Compton effect and electronpositron their production therefore has a dual nature since we have no many experiments which demonstrate that light is a wave meaning that door nature means it's both particle and away planted around the body suggested that particles like electron also have wave properties of the airwaves wavelength each over the moment this led to the development of the from microscope the principle of complementarity requires understanding 1 particular particle always needs to take into account both particle as well as the and that is true for you the light of matter the experimental set up decides if a wave or the particle nature revealed last leader the early scattering experiments revealed that for the structure of Adams that the positive charge of the Adams concentrated in a small nucleus which is surrounded by a cloud of all problems and the bore some of the model off the actor has electrons orbiting the look like true of solar system standing teletron waves using the volume off electrons explained why the energy and the angular momentum as well as the radius is quantized the quantization competition for the energy level it's like this Mrs. be ionization energy of hydrogen and this model is able to explain the atomic aligned spectra so now we
21:37
will move further inside me out into nuclear physics nuclear
21:44
physics and Darrin Murray directivity just reminded you a rather Florida found out that most of the mass of the Adams has concentrated in the years since the reality don't contribute much of and atomic physics is about the structure of the clown surrounding the nucleus and Nokia physics is about the structure the nucleus itself so that this this is what we will be talking about not so as a matter of fact and in Tokyo's consists of a smaller particle growth not smaller particles called a Nokia and becoming into varieties 1 is called proton called neutron for autonomy it is positively charged by air With 1 elementary charm neutron is neutral has no chance at all therefore the protons are responsible for the charge of the and neutrons Our country there was no clear answer may also consist of small things grow smaller things are called walks free quarks make up 1 and the 2 types of quarks Faulk and Dunkle Coke has challenge over twothirds times the elementary lounge don't called the chant of mine is 1 of the shot and therefore the Proton is made up of EU wasn't 1 D and therefore it has a total charge last year and the neutron is made up of 2 . 4 1 up and therefore it will total and both the locations as well as the quarks are from him just like unlikely can described the atomic nucleus uh fired tool numbers the charger numbers he identifies the element and gives us the number proton and atomic No. 8 identified the actual look line the difference between a and Z gives us roughly the number of neutron so actually wanted off a little you and it is defined by chemists exactly 112 of the mosque contained fell 6 problem that is roughly 1 . 6 6 times 10 to the minus 27 either talks have the same charge the nucleus but they have a different values story as a table of those articles electron proton and neutron just as Angie sample hydrogen atoms and here it is dividend programs and here it is given in those atomic Marcy units and here it is given the energy of the speed of light square and you will notice that the neutron also slightly heavier than the proton Gizela traumas much less I lighter than you the proton or neutron these density off nucleus is very high and have fun came estimated density of the Milpitas by measuring its size with scattering experiments just like rather scattering since 80 is roughly the number of nuclear arms and that is true because 1 proton raise about 1 Thomas lasting and 1 neutron weighs approximately 1 since you can measure the size of the bill clears I can't find this experimental relations that no plea is roughly feeder operators part of it killed of the radius is given by a 1 . 2 firmly Q times must No. 8 and affirming it is 10 to the minus 15 meters or ballot that 5 orders of magnitude smaller than the diameter of that this relation implying that the volume of the nucleus proportional to a meeting for the number of nuclear arms and therefore no clear answers can be modeled as hard spheres that don't penetrated so I the largest natural look Lewis has a vast number of 430 8 and that's uranium 238 and using this relation to find out that it's about 6 . 2 times bigger than that no clears hydrogen which is of course just a single proton let's estimated that density of Tokyo matter and compare it to that of normal solids secrets novels solids liquids have typically about 10 to the for kilograms meter fuel for Nokia matter Marcel Proton and be there use this formula which relates a radius Of the nucleus feel to the mosques number and if planted must novel 1 and this is just the volume of steel for times readers the power than we get about a twopoint lead times tend to the 17 kilograms of that's about their 15 orders of Man which would soar above that awful regularly could solve we can make this estimated in a different way also can simply stairwell Adams sort of just about against each other and you know the size of a matter typically 10 to the minus 10 meters twice the ball radius there has since the size of Tokyo's typically 10 to the minus 15 meters and simply take the ratio of that for the 3rd power to give us the volume and that gives us also about 10 to 15 orders all of which will be 1 of them them in the article Nokia matters varied dance so you may ask yourself since we know all that the only protons and neutrons in the Nokia the protons up positively charged for come the electrostatic repulsion between protons that doesn't blow the power what keeps it together and the answer to that question is there's another force make sure that a distinct from electromagnetism and it's called the strong force it is an interaction a similar electromagnetism but not saying there's actually stronger than Elektra Myrna Mack In the same way as elect Amanda's is stronger than gravity and electromagnetism we have that 1 signed electric charge Rostron force however was more complicated has resigned challenges and those are typically called Carlos because the red green and blue those charges a strong and the protons and neutrons we are not just made out of talks which have been rare electric charge of those courts also have color their red quarks Queen of quarks and lukewarm actually proton and neutron made out of quarks 1 each color of
29:50
how this looks like a proton and has therefore example red quark and we knew quirk of rule down and so it has total electric charge plus 1 and and has total White because red pleaded green and blue scholar neutral white and when I talk about those Carlos's knowledge is not the same as the colors that he sees him on the simply a reflection or these rules how calculate the boss color for the neutron they also 3 colors both a neutron proton color neutral soaring principle the strong interaction doesn't have anything to say about protons and neutrons just above the quarks inside however it's not a static system protons and there are fluctuating at colored by all multiples sometimes the bottom part discovered sometimes it's color some of the rule and ended there it always changes for both proton and neutron but if you sum up the corresponding and interactions between protons and neutrons and come up with noble traction and that is a somewhat similar To be the case of atoms attracting each other atoms are electrically neutral but
31:30
they also called on the hottest attractive forces between atoms or molecules futile fluctuating electric dipole such such forces are always short range and nature so they don't probably reach out to infinity like electromagnetism their only Arab rope at short distances and that typically quite weak demand of us force much weaker than a typical electrostatic force however since sister of thought now they have a different in nature so they're different qualities so red Charger you cannot express a charge with red it's a different thing yet 1801 1 can be positive or negative can have a positive red or you can have a negative and positive to negative unlike for the electric charge would close enough To give 1 mumbo for the electric charge for the color children freed from under red how much green and how much each 1 is fundamentals you cannot express the SS said of refined allows forces Sheikh and therefore we no clear force this week compared to the full fullblown strong force however even that small residual effect a strong still enough although power electromagnetism and so if you look the potential enemy 3 or 4 proton and neutron as a function of distance between them potential energy distance them over short distances attractive force is old following electromagnetism forms well and then once you get beyond the radios course effective then to get the normal world repulsion between them between nuclei so I a field day the combination of those we see a potential area this part of the of potential energy wealth and so I once of bond together in book is they're sitting down and that in this well and as long as there don't people off this is area will stay contained the binding energy off of the book visitors is quite large 1 can calculate we must equivalent to the binding energy we have a binding energy Yvonne we can calculate last corresponding rise and bond which is simply energy divided by the speed of light square this binding energies so large that it cannot be neglected when calculating muscle for so the total amount of a stable Nokia's is always less than the sum of the and that 1 can even it was a stability criterion meaning the more binding energy you have looked on Wall must loss on the more stable the look and that typical value for the binding energy and personal plea on its aid and you see it varies as to whether this across the different look plot the must number or the number of nuclear arms on the horizontal axis His binding energy and its peaks with irony in that it has Areas seeks rallies on so instead of for calculating this example I of finish you experiment and that is to
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demonstrate please Bert not all look assists uh remain intact for ever
36:03
so it was discovered that some look unstable air disintegrated after some time there are 3 different types of searches integrations which recalled alpha beta and gamma so this 1 is a melphalan middle and here I am particle detector mom on me this and 4 of a fully answered a terror let's 1st column B uh uh back concrete so as such radioactive events had happened naturally in the environment all the time so let's just will column without inserting the unstable and we get a vote my colleagues colleagues have 6 seconds a if I consider this a these unstable iron and cloned again earned their each each count is 1 that is integrating new could have followed a thousand 600 columns and 6 seconds abolished a 60 counts per 2nd also called uh that corrupt so this is an alpha emitter and I'll Fly resulting radiation we will talk about that next time what that radiation is his easy shielded even buy a piece of paper and answered this piece of paper and the new bill already see a reduction in and the Contras or risk the paper hair of robot 60 columns 0 6 seconds or a tender coral saudis woes 600 6 source as a simple sheet of paper and then shield you from from this radioactive element so that means that your skin is a good protection it and the only danger was such radioactive elements opposed if you get them inside your body so I guess this is a different type of of radioactive element and its Arab disintegrates a different ways Sophie's of paper is not going to shield this on so 1st of all the activities this as something like 360 columns and if I put a sheet of faithful in them now the there goes no there's not much difference slack as slightly less but not a not very much difference however if she ever put it he put a metal sheet on top of that a aluminum then Marinovic counters videos it's not only about 60 counts so lastly of showed a woman stood type of Nokia disintegration Rice's called docks and this 1 is called Gum 1st column directivity result a any shielding and it's about a hundred columns and putting my metal shield on top of it doesn't make much difference so gum on radiation will get very conscious that metal shield ended actually require said heavy let shielding shielded you in that 1 doesn't shielded completely still get about half the columns and try and foot a walmart let shielding on top of that still In between saw some offered is still going slow so I
42:12
alpha radiation when it hits your body is does the most damage but it's easy shielded a Bader radiation is penetrating but it does less damaging your body and gammaradiation that's the least amount of damage but it's very difficult shield and typically requires very dense metal break shield thank you for your attention
00:00
Collision
Hydrogen atom
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Canadair CL44
Aschenwolke
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Divergence
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Temperature
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Gaussian beam
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06:35
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21:35
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29:48
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35:47
Alpha particle
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42:11
Ship breaking
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Hitzeschild