Mystery of Physical World Lab
Mystery of Physical World Lab ISP 209L
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This 63 page Class Notes was uploaded by Ms. Mckenzie Labadie on Saturday September 19, 2015. The Class Notes belongs to ISP 209L at Michigan State University taught by Staff in Fall. Since its upload, it has received 115 views. For similar materials see /class/207733/isp-209l-michigan-state-university in Integrative Studies Physical at Michigan State University.
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Date Created: 09/19/15
Today We will prove that light acts I I like a wave again This time B I y we will shine our laser on 2 closely spaced slits Let s assume that they are very narrow so that the single slit interference pattern is not noticeable Huygen s Principle The narrow double slits act like 2 distinct point sources of waves We will again get an interference pattern Lets look more carefully How does the interference pattern emerge Constructive Interference Q Bright area Screen Destructive Interference min o x I I n v min nnnn n u s H 1 a s 39 r r mommmmscme Dark and bright spots LC alternate W 200 1 human Blanks Cure The Math Light from 82 has to travel farther than light from S1 The path difference is 8d sine P Source 82 I 5 l L Constructive interference occurs at point P if 8 0 or if 8 is a multiple of the wavelength 7L 9 d sine m7 m0 i1 i2 i3 uewummm Double Slit Interference The rings cross at some 1 r M 4w f a E places giving iiQ llaEEDV1iIirtu El5 In page D RENE Haw5 extra amplitude to the wave A pattern of bright and dark spots emerge min a fi 551 J39s1 WEE itE 3 5quot E E1 F4131 1E i yELEtHu quot2 5 531quot 53 1quot Double Slit Interference Amazingly light is not the only thing that acts as both a wave and a particle Everything is both a wave and a particle Diffraction Grating Let s go crazy and put in lots of slits Incmmng plan mwo ligll Light diffracts l D 25235 and we get i 39 new interference through each l of the slits between each of icmml or E 711335quot the diffracted Al quotFm waves A device like l r 7 7 Eil tii fi f this is called a swimquot a diffraction grating quot39 quotquot J A x Again there s a path but there s both L length difference diffraction and between light passing interference taking through different slits place bright lines or spots when d sinEbright m mmmmsmm m012 Last Week Last Question Why did you see the colors of the rainbow when white light shined through a diffraction grating Interference Pattern Red Light Let s shine a laser on the grating and consider the rst bright spot m1 Remember the grating and double slit patterns follow the same math a gt gt I d sinO 9 sine A d Interference Pattern Blue Light Now let s use a blue laser Why is the angle reduced at gt d sinG 9 sine A d Interference Pattern White Light We can assume that white light is a mixture of all colors therefore it is a mixture of all wave lengths llllllllllll I d sinG 9 sine A d Radioactivity In 1896 Henri Becquerel while investigating fluoresence in uranium salts accidentally discovered radioactivity Work by Curies and others showed that radioactivity was the result of the decay or disintegration of unstable nuclei Up to that point atoms were believed to be forever indestructible Radiation Types Alpha particles are helium nuclei 2 p 2 n we Beta particles are speedy electrons Yeeeeeeehaaaaaaaa Gamma radiation is a stream of photons Example 1 Alpha Decay A A4 4 2X z 2Y 2He X is called the parent nucleus and Y the daughter nucleus Example is Radium decaying into Radon and an alpha particle In order for alpha emission to occur mass of the parent must be greater than combined mass of daughter and alpha particle q excess mass converted into kinetic energy most of which is carried by the alpha particle Before decay KERn pRn After decay 92m Wmsm r sums Cale Example 2 Beta Decay A A gt ZX 21 X e Before Decay Examgle A neutron turns into a proton emitting an 3 electron 1 1 0n 1p 8 After Decay gt H alf l if f a radioactive sample N contains N radioactive nuclei at some instant the number of N0 nuclei that decay in a time At is proportional to N NN r h o ANAtu N U 0 AN 7NAt o where x is a decay constant NO quot R ANAt AN 0 rate of which atoms decay NNoe T12 half life is time it takes l for half of sample to decay I Decay constants vary greatly 39 for different radioactive 712 2732 decays and thus so do half 2 quot 39B39 E lives 0 Lgtlgt l Radioactive Dating We can often use radioactivity to measure the age of an object Consider 1 C dating o cosmic ray interactions in the 14C 14N upper atmosphere cause nuclear y e V interactions that produce 1 C 12 7 14 Wm N The greaterthe value o IIVIng organisms breathe In carbon dioxide that has both 120 Of 14C 12C the more 14 I and thrad39 a quotquote C recently the organism 0 so all IIVIng creatures have the same ratio of 1 C to 12C died 13X103912 o when the organism dies however it no longer absorbs carbon dioxide from the air and so the ratio of 14C to 120 decreases Carbon14 Dating Works on samples from about 1 to 25000 years old 9Why not longer 9The halflife of 14C is 5730 years After about 5 halflives too small a fraction of 14C is left 2532 so lt132nd left Example Dead Sea Scrolls date to 1950 years ago Geiger Counter Mic wlndnw mm Elan rude at lnlid m MutllTnhc antlv supply mqu aupnvy Device used to detect ionizing radiation Consists of a tube filled with Argon gas with a central wire at a high voltage When a charged particle passes through the gas it knocks electrons off of the Argon atoms The electrons are attracted to the postively charged central wire and are accelerated towards it They acquire enough energy to knock more electrons off of Argon atoms The result is an avalance of electrons hitting the central wire which creates an electronic signal Final Exam Format and suggested review material General Information The final exam will take place during the last class April 23rd at the regular class time of your section The exam will be closed book It is intended to be a 45 minute exam However you will be given as much as 90 minutes to complete it Formula Pages The exam will contain a list of useful constants and formuli In addition you may bring your own formula pages up to two 85 x 11 sheets The front and back of each page may contain formulas or any background information The material must be handwritten Final Exam Exam Format The exam will consist of approximately 24 problems About half of the problems will be multiple choice or truefalse Some of these problems will be very similar to quiz questions About half of problems will require calculations similar to ones performed in the labs Suggest Review Material Material that was covered during the introductory lectures and during the lab itself are fair game for the final exam Recommended material to review 1 The introductory lectures 2 The main physics ideas and the main calculations that were performed for each lab 3 The quizzes Today Electricity and Magnetism Electrical Circuits 9A circuit is always a circle Basic Ideas 9A battery provides work to move charges Q around the circuit The units here are volts V which equals the work per unit charge To confuse college students the common name B 39I 6 V quot C for the physical quantity comes from the name of the units voltage V To g the right we assume the battery quot39 provides V 6 V A o 0 V o If 9The black lines are wires We assume the voltage never changes along a continuous wire 9The charge passing a given point per unit time is the current I The units are amps A R has units of Q 9The jagged symbol represents a 0 V This could be a real resistor The vtoltage does change resistor 01 something across a resls or 11ke a 11ght bulb 9For convenience lets define the green ground as the zero volts Electrical Circuits Ohm s Law I gt Ohm 8 Law B 6 V C The voltage change across a gt 39 tor39 V ltgt reSIS R jgt V I R A 0 V D R has units of S2 39 0 V This could be a real resistor 01 something like a light bulb Electrical Circuits Power Power 9Charge Q gains potential energy QV while being pushed across the batteryThe rate at which energy is gained is QVt QtV IV Remember energy pertime equals power So PIV 9ln turn the charge loses energy while crossing the resistor The rate at which energy is lost is also PIV 9We can also write the relationship as P IV 1IR 12R 9The energy is changed to heat for a typical resistor For a light bulb it is heat light VVV R has units of S2 This could be a real resistor 01 something h39ke a ght bulb Resistors in Series What happens if I have more than 1 resistor in a circuit Note that the same cunent ows through each of the resistors in series Resistors in series are connected end to end IR 1 IR2 2 AV I AVR1R2 AVReq b a 2003 Thomson 7 Brooks Cole Requ1R2 For resistors in series the total resistance increases and thus the Current decreases Resistors in Parallel 12003 Thomson A Brooks Col Note that 1 the resistors are connected at both ends 2 the current through each resistor is not necessarily the same and 3 the resistors have the same voltage across them I II I2 AVReq AVRl AVR2 1Req lR1 1R21R3 lR4 Req is smaller than any of the resistors Magnetism And now for something completely diffe Even if you haven t studied magnets in a class you ve encountered them o magnetic poles come in two types N and S A N poles repel N poles S poles repel S poles and opposite poles attrach o a magnetic field stretches between N and S pole A shown by iron filings in this case 55633 llmmson E mks Co a Today Low Temperature Physics Temperature Scales Most of the world uses the Celcius scale rather than the Farenheit 9 Water boils at 100 C and freezes at 0 C 9 T C59 T F 32 Most of scientific world uses Kelvin scale 9 Same degree unit as Celcius but 0 absolute zero Temperature we ll be working at today 9 What are effects of these low temperatures on materials Farenheit Celcius Comments Kelvin 212 100 Water 37315 b0is 32 0 Water 27315 freezes Liquid 30042 19579 nitrogen 7736 boils Liquid 45211 26895 helium 42 boils 45967 27315 Absolute O O Quantum Theory In the quantum model of the atom electrons can exist only in certain stable orbits While they are in these orbits they do not give off radiation When they jump from one orbit to a lower one they emit a photon of light of a given energy Semiconductors Something similar holds true for the collection of atoms in a light emitting diode LED The electrons can either be in the valence band lower energy or in the conduction band higher energy but not in between 9 The energy difference is called the band gap Thermal energy can cause electrons to jump from the valence band to the conduction band When they fall back down they emit a photon of light equal to the band gap energy 9 This photon has a wavelength in the visible range green at room temperature which makes an LED useful Conduction band WWV Azg reen at room temperature Valence band Semiconductors The band gap separation decreases as the temperature decreases meaning the energy of the emitted photons decrease This gives a longer wavelength to the emitted photons What happens to the color Conduction band WV A Valence band Superconductors For metals as the temperature decreases the resistivity decreases For superconductors the resistivity falls to exactly zero at some critical temperature 9 Not close to zero exactly zero Rm 015 0125 010 0075 005 0025 T I E m 000 40 41 42 2003 Thomson Brooks cmK 4 44 TABLE 172 Critical Temperatures for Various Superconductors Material Zn Al Sn Hg Pb Nb Sn N1ch YBagCugO7 BLSrCa Cu O Tl B a Ca Cu O HgBagCa2Cu308 2003 Thomson Brooks Cole Tc K 088 119 372 415 718 946 1805 232 90 105 125 134 Superconductors Particle accelerators use superconducting magnets Superconductors In addition to zero resistance superconductors are perfect diamagnets Superconductors Diamagnetism Besides ferromagnetism there are two other types of magnetism 9 paramagnetism 9 diamagnetism Superconductors are perfect diamagnetics 9 This means they really really hate magnetic fields and will do anything they can to get rid of them Superconductors Diamagnetism How does this work superconductors hate magnetic fields and will 5 ma net do anything possible to D 9 push them away N 9You can push a magnet away by creating another magnetic field Superconductor 9 Remember that current loops produce magnetic fields Last Week Some problems There were many problems with significant figures units and showing your work Here is an example from the pendulum experiment 7 Calculate the correction factor 5 009 Last Week The free fall measurement of g experiment posed questions about how the rotation of the earth affects gravity The main answer is that the spinning of the earth does NOT cause gravity Gravity is a fundamental force that only depends on mass and distance Last Week The Earth s mass causes gravity which causes apples to fall to the ground But the rotation ofthe Earth does give an effective force that competes with gravity and slightly reduced the apple s acceleration gGmERE2 983 ms2 What is the effect of the rotation of the Earth on the measurement of g o a v2RE centripetal acc a 463 ms2636X106 m a 034 ms2 compared to 983 ms2 NB rotational effect strongest at equator weakest at the North and South poles O O O O Last Week Suppose i want to induce artificial gravity on a r I 1 7 V space station T x 394 j 39 I can do that by starting it r i gt MC quot 39 rotating xiiii I want av2Rg o av2Rm2Rg o o2gR98m52100m 098 radsec o w3 radsec o 2 radrevolution f 05 revolutionssec Today Sound Sound is a longitudinal wave 0 Air 20 C 343 ms Seawater 1533 ms iron5130mls The speed of the wave depends on the medium Movie Longitudinal Wave l x z h39hl in s The speed of the wave depends on the medium Frequency f HiglFraIuencyWave o T period 1f Time 0 Remember that E product of FM wavelength and frequency is always manququave the same vveocity Time of wave E Detecting Sound Two Facts The strength of a sound wave is measured in the power it carries in a given area this is also known as the intensity In SI units intensity I is measured in watts per meter squared Wm2 Our Ears The human ear can detect an amazing intensities range 103912 Wm2 softest9 10391 Wm2 Ioundest This is a range of 100 billion 80 intensity is NOT a convenient measure of loudness Instead we use decibels ll Decibels 4P Sound levelD10log10I1012 l units are dB decibels The decibel scale is logarithmic So a sound wave 1000000 times greater is said to 60 decibels louder Note that a sound wave with an intensity of 103912 watts per meter squared is defined as 0 dB Threshold of hearing gt 1 X 1012 Wm2 0 dB Whisper gt 1 X 10quot Wm2 20 dB Normal conversation 1 X 10396 Wm2 60 dB Large orchestra 63 X 10393 Wm2 90 dB Walkman at maximum level gt 1 X 10392 Wm2 100 dB Threshold of pain gt 1 X 101 Wm2 130 dB Announcements Happy Groundhog Day Pick up old labs at the end of class Why not start preparing now for the final exam 9Read through the old lab again making sure you know the answers to the quiz questions Take another look at the lecture notes on the web and see if they now make more sense We were lenient in the grading In the future be sure to Answer question explicitly being as quantitative as possible show your calculations Rarely if ever will more that 3 sig figs be appropriate Light Some History Early 1800 s Light is a wave traveling through the aether not quite right 1865 James Clerk Maxwell Light is a wave of electromagnetic radiation yes 1905 Albert Einstein Light is both a particle and a wave PARTICLE WAVE Electromagnetic Spectrum All electromagnetic waves travel through vacuum with a speed c 3 X 108 ms The visible portion of the spectrum forms a tiny portion of the total EM spectrum For all EM waves ckf true for any type of wave 7 cf my ur H Frcqucnry 11 t l l Gunnna um ancienqu I lirrnwm N F Visible Light lit AM Radio waves 105 i I not 101 7 Long wave 2003 Thomson Brooks Cole 1 pm 1 angstrer A l mu l m 1 cm I m 1 km Views of Crab Nebula Xray optical infra red radio increasing wavelength Reflection and Refraction When ever light travels from one medium to another two things can happen 9 Reflection 9 Refraction Reflection Draw a line normal perpendicular to the surface Consider the angle between the incident ray and the reflected ray The angle of reflection is equal to the angle of incidence 91 91 9 just what you d expect if light were a stream of particles bouncing off the surface Specular and Diffuse Reflection Refraction Some of it is transmitted Incident Normal Re ected refracted into the 2nd ray ray medium Not all of the light is A l 9 reflected at the surface 91 l 1 Note that the refracted x angle is not equal to the Air VI incident angle Glass v2 In fact the angles are Egg related to the velocities l of light in the two media I B 9 sin e1sin 62 v1v2 39 Refracted ray 2005 Thomson Brooks Cole 3 Refraction Can be understood from wave properties of light Wage Ed 3 The angle changes BEES 39 because light travels W SLOWER inside some 7 quot 7 materials than others The speed of light inside any materials is always less than in vacuum Watre Ed Fly0 vinside lt C 2 Bends Exit Refraction Snell s law Incident Normal Re ected Light travels at a speed c in my my vacuum but slower in other media A Define index of refraction n 61 cv where v is the speed 39 that light travels in a given medium glass water etc sin 91sin 92 v1v2 can be rewritten as B 93in 91sin 92 n2n1 Refracth 9m sin 91 n2 sin 92 my Glass 1 2 2003 Thomson Brooks Cole 3 Refraction The angle can change in either direction depending on the relative index of refraction or speed of each material Normal I I I 01lt02 I I I 0 I I Glass I I Air IQ I I I I I b 21 2003 Thomson Brooks Cote Reflection and refraction Fig 226b p691 Total Internal Reflection When light travels from a medium with a larger index of refraction to a lower index of refraction it bends out Normal Normal 1 Low index of refraction l l l l l l n2 l 92 3 l l l l l l Higher index ml of refraction W1 01 At some incident angle the refracted angle is 90 9For any angles greater than that no light makes it into the refracted medium 9N0 REFRACTED LIGHT 100 of it is reflected
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