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Basic Physics III Lecture 10

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Below so we will continue our discussion on electromagnetic waves And the last time we looked at a plane sounds audio
2 Then Said here I'm sure you simulation job out there will show you Mainly so you Maddox south and north the color and electric field rector of the arrows and of problems is probably dominant if you want look at that applet you can look On EU Web page at that calm and flavors Start a for example you can look at not just as a plane waves but you can also look at oscillating dipoles
All standard antenna
Or current rules so that their careers
The nations That can simulate For the antenna You can also change the length of We aren't enough All you in the direction of And and see the results Inc Electromagnetic waves with so this A little at that Seoul's not Maxwell's equations For you let me a prickly some eyes But 2 days ago I looked at Dallas's Awful electric flux review electric fluxes are calculated closes a close a lot the U.S But equals A totally enclosed Divided By that not and dollars is All medical rocks Always come your on other worlds There no chance There is a lot tells us that changing medic flux wrist Same all Cutler Grades A circular electric fields or a wrong Bomb and at his lawyers reversed so if you have a changing electric shocks and you get The magnetic field also if you have an electric current should also make such a Mom Hermitage show that both these electric and magnetic fields satisfied wave equation and also each component of but not going shoulder here for another worlds A partial the root that time twice equal sees career At times A 2nd spatially And Korea equals about 1 0 and you're not on the propagation of electromagnetic waves and in America But it comes out to be the speed of light therefore electromagnetic waves and light from the speed and finally viewers who playing some sort always Just showed out then media Electric output told is related The magnetic out through the and the last time we also talked about the various wrong an elected expect from rich A goes only AC current and car the wall all the way to reverse worry about frequency And this Time I just wanna point or leave the visible spectrum so laser lined up I'm using this lecture is actually a roughly This man The spurt from more 445 amount of but The year the visible spectrum For The shortest way is not visible humans 405 this is 1 of the 5 nominees go further and the rules lose on longer wavelength What we have the Then a greater sensitivity Organizers in the green of 5 on the tools and then that's a good amount of wavelengths to go to the yellow and orange or in this case is 595 and eventually at a boat 700 not only stew when I cannot 1st Steve So this this 615 amid already appears to be region just You go above a visible spectrum infrared and ultraviolet cannot see but B physics subject of object actually of optics deals with both A horse that From the importance of Saunders Zeus wavelength region optics has something to to say so that man
Calculated and 1 more example of followed the a spectrum of select grace But cellphones usually received electromagnetic waves Quarter antenna means that the length of Straight and The length of a brought corresponds to a one-quarter of the wavelength of electric grid receipts and If a cell phone has such a brought cannot be part Long estimated operating frequency The fall Since we know that Length Member will fall That The radio and must be be 4 times the the length of the antenna or what Kind 0 . 0 8 5 which is 0 . 3 4 We cannot calculate frequency of that corresponds to the wavelength simply by dividing his Lead of life or elect grace by this point 3 4 meters And that gives us 8 . 8 Find Tend All of a sudden it CD and go So cell phones Operated in almost a year gigahertz frequency another interesting subject there's actually Measure relied velocity missus not all that easy Really Plight 1st and what he used to People on our and neighboring covering uncovering back and he was then trying to find out What this means speed From my receiving such flashing lights and you concluded that time delay was observed Was consistent with human reaction time and therefore that these We must be launched or reps even The time of the next guy somewhat later For a and he or observed Their eclipses of Jovian moon Iowa Which has Davidian eclipsed therefore full plant of all along Jupiter and there's an apparent wobble and these orbital period All of this More which comes From a finite speed of light so our party called here is that if birth Is Approaching Jupiter What is The orbital period When receding from because work Is approaching Jupiter You go from all widow or with each time you However the negative time You can't get close to Jupiter and therefore The actual Karim's doesn't have trouble spot Small and on the the other side of is moving away from my Then I'll be orbital period appears Just a little bit longer And from many years of observation and he concluded And time delay from like trouble It is about 20 minutes Times With Angle of between Earth and Jupiter divided by time So a maximum It The time delay from year to year and minutes From at minimum of course No time delay didn't make any congruous for the time delay from Jupiter from Both did A little value for the life velocity itself then 1 of the most successful work tends to measure the light varsity was done right here in some form of Michael's determined the life of varsity using rotating 8 site
Member of the ideas following you have a light source Sitting on Mount some mountaintop Before Light Reflects of rotating and if the angle was just right A neighboring house Vendors carries And then in bonds of that but stationary of Friendly He's light speed and your occasional speed of Are matched just right Flash Bombs off this Basis The 8 Aristide rotating room and Injured Select carefully Tulane B rotation speed of this rotating can determine that time That is necessary and therefore the speed of light it can all the distance between Bomb So this is 35 kilometers and because the virus our about twice NATO where 70 kilometers time for 1 8 term and must be able to leave said And Please This is what they term that means We that was Angular frequency with which this book and on Work this time I have fought I'm stoked So I'm not all these actually visible from here after the lecture to go out on the chance of repeating miners and Roland concede falling is still modern value would be a light velocity A 299 Million 792 thousand 458 meters per 2nd And this is no longer a measured value of this is the exact number and the reason for that can measure time so precisely that we actually defined you wanted of meat by a defining a unit of Time and multiplying this with the speed of light with this speed of light This is the exact role in of infinite precision Another interesting thing about the speed of light Based on the result of the Einstein and experiments Michaels More than the speed of light In vacuum this constant and independent of The frame of reference And in particular there can be be no faster signal speed The speed of light ourself Like these that cost speed make an example about the speed of light make a telephone call from New York to a friend non estimate how long will be the delayed due to the electrical signal traveling back and forth between your And plant part a you assume that telephone call this carried by cable underneath the Atlantic Ocean and in the case of the EU assume it sent via satellite And the Allied and geostationary orbit about 36 thousand kilometers And the questioners this Cause a noticeable delay in the case but still only on a fairly simplify things we assume that the speed of light is the speed of light and vacuum that's not strictly full annually by traveling through the atmosphere and Were traveling on cable in the Atlantic Ocean and elite distance from New York 2 Larned on soon-to-be of our heartfelt kilometers and If we divide 5 thousand kilometers 300 thousand kilometers the 2nd we get a fight with 3 hundreds of a 2nd or 0 . 0 1 7 For the beat tool out for satellite in geostationary orbit and replied 36 thousand kilometers divided by 300 thousand km And of course we we have to do it twice because the signal has to go to the satellite and back from the satellite and together A time delay of 0 . 2 4 said so this time delay is so short that it's probably not noticeable talking on the phone but for the 2nd It's quite long so in the case of Satellite calls there is noticeable delays due to the speed of light we talked of quality energy transport of waves and election medic on differently also transport energy and I remind you that the energy energy density of electric field is given by by an epsilon not time electric fields prayer right to late And magnetic fields Energy density this given by a magnetic fields square Divide by 2 times not been all that electric and magnetic field adequate food Our related by Therefore we can Expressed These electric field square divided by a script by magnetic fields And since we Inversely related to epsilon not terms that means that the magnetic fields career must be be kept I'm not times you not time script From that we can That those 2 energy densities in the case of electromagnetic waves I equal to each other and the total energy density is therefore at ease career without a division to all these girls And of course we can also expressed that the speed of light so if you now will look at the energy passing fool an area And the time of the team That means they consider a volume consisting of the The area and the robbery since lies in the propagation direction off Speed of light time T then be if we multiply this Energy density That's not ease new not with With the volume than they get A you Times a C T Times Pte If you know where those 2 factors He and a then that be plugged in the expression for a total energy density and In this fall on the speed of light cancels and here and we just have he'd be divided by And not this From Area and this is the time difference so if you want Get something like a power walk area which is related to intensity you remember from a discussion of the same phenomenon Jamil Powell
Her area is keen Dean divided by weekend then add define us the so-called pointing Across Are between electric and magnetic field divided by you not And we know that electric and magnetic field full of Electromagnetic waves are perpendicular to each other and perpendicular to the direction of propagation so for this Pointing rector since its across product perpendicular He will be a points in the direction of the art of property and the magnitude of This is related A tool intensity which Powell prayers But If you take the time averaged magnitude of on appointing rectum get the intensity of the from quake So for example for sine wave intensities Given by this time our relations Just for convenience not Out not than you not Times's time coverage is the electric told times we were Meddock Times the time average of signs grip on TV and if you look at the signs Where function I've been plotting a tear and little in search of NUC that it just goes wrong The value of 1 heart obviously the maximum of science still 1 minimum with Zero and at a time average value 1 so I can replace This time averaged about 1 half And that means that The time averaged Pointing to eat not be not divided by 2 times And you If it defined now would mean square values for electric field and for the magnetic field which is the average of East career and coverage of these squares These would mean square by square But we can express This time average The point is that we are a product of Those 2 would be scrapped about electric and magnetic field Divided by not so let's consider the radiation that ahead hitting theaters From the start Still outside of the atmosphere be an intensity of solar radiation and stood in 150 What's the meat square If you assume that It's a set single electron magnetic wave that is responsible for this summer radiation intends to calculate the the maximum values Of the electric and magnetic fields The way you do that is so we know that We time average The magnitude of the pointing rector this one-half salon not square and You not sway therefore It's twice this intensity twice the 1350 bought square divided by not it public it is this formula all that leaders of the finding Lecter Equals He crossed And so the magnet told Each time said Me and in all that He not be closer be not time seem so that so therefore I can replace that I can replace that growth See times and East square and since I since I have also the fact of you not there And and all that Squared equals 1 all Epsilon not And you not I can have removed glass Pecanwood replaced 1 although you not Lewis That's not See scored so that's why this this fast
For the speed of light appears The denominator aren't solidarity put it And in this part of the formula However we value for the electric field is actually correct its 1 . 0 1 for me And if I want to know what it is Magnetic field maximum then this is Electric field maximum divided by the speed of light so it's this uh 1010 and both leader divided by 3 times and and meters for 2nd we all wall units are Tesla And I get a magnetic field after of 3 . 3 6 Ferreira 1 . 0 1 kilowatts needed for the electric ample food and feed these 6 and might test for them magnetic field So even lower Values look very different by orders of magnitude it is Just coming from the definition of the units As for all electromagnetic waves also solar radiation that's as much energy carrot and electric field The magnetic field but Talk about something else that you would Affected electable mentor graves And transmit energy they also carry and our Maxwell Pointed out that Is the electromagnetic Energy you'll is completely absorbed then add the object of absorbing ought to receive the momentum transfer of a divided by sea and if it is completely reflected it ought to receive a momentum transfer Twice times you divided The most general case that momentum transfer equals 8 times you see plays at some number between 1 and 2 so 1 complete absorption and was complete reflection and parcel reflection and absorption number Some lean and mean Olivet The force It's the momentum transfer divided by the time required for Momentum plans 2nd law so we can calculate the pressure the resulting pressure which is the 4th divided Our area and if we consider the same the same volume element Ontario amended did apparently discussed G Entergy transport pilot from what it
Then we can replace 1 over the area with delta T over the volume we simply do was be multiplied tea in the normal rate and the denominator and then we get the volume and the denominator don't Laura F times Delta team however
The momentum transfer from 2nd and Delta equals this so we get these resulting pressure of 8 times The energy you divided by abolishing right see you would abide by a volume is the energy density and so know what that is we can therefore expressed in terms of the year pointing back and it's just 8 Average man of the point that Do I seat So this is called Radiation pressure And Radiation pressure Can be used Am Monday put small things if you have a tightly focused laser and use it to move around atoms or molecules microorganisms and the technique is called an optical tweezers Even Though the forces are quite small masses of those objects also small and therefore and you can Grab very kind things So as an example full radiation pressure there have been about proposals to use radiation pressure from the sun for help Propel spacecraft around the solar system of costs you can only move away from the sun but it's kind of like sailing in space So that the question is how much force Would you expect for about 1 kilometer square Highly reflective sales and How much would this increase the speed of 5 times and spacecraft and 1 year And if this spacecraft starboard from rest A whole go and London And to answer those questions 1st A look at the the forces Pressure upon area and in all of these pressures In this case and highly reflective given by twice the magnitude of Pointing that derided Times The area Sales in all from the previous example that appointing Richter magnitude 1350 what per square If we Then multiply The area of the sale which is with the Lien leaders square and then divide by the speed of light become up with the force And I knew its mother a large for So we can calculate the acceleration a neutral force of mind you simply ratio mind would survive a Kilograms and this is 0 . 0 0 1 8 Meters per 2nd square So if you multiply the acceleration of 0 . 0 1 8 meters per 2nd square with the time off about 1 year that is a 3 thousand 600 seconds Our Times 24 hours times We under 65 . 2 5 days coverage year than we get a speed of 56 . 8 kilometers The 2nd this is quite a significant speed calculated that In miles per hour would definitely breakfast or even tho the force is small Because it is continuously applied over 1 year you can get a large speeds and indeed you can if you calculate how far goes With their usual formula 1 half times acceleration Times Square To plug in the numbers you get Total 8 . 9 6 times 10 to the A kilometer So that's also a really long distance So it is quite feasible Even for A comparatively heavier 5 pound spacecraft People help through the solar system if You can them Manufacturer 1 km square sales which is also Develops much much larger than any sale invented by humans or ships so let's talk about receiving electrum admitted in Olivet antenna ask can emit electromagnetic waves supply them with a scene that receive electromagnetic waves All you need On 10 also because man carrying 20 election medically and the electric field I will produce an electric current India can now and you can bend Amplifying a AC Current an amplifier and have something that is proportional to the electrical magnetically being received by 10 or you can make a real Montana like this and If a magnetic field is going through that and induces a voltage Which then drives current convey an amplified this is usually done for radios This is to flee on foot to theirs Somewhat longer history of using electoral degrades on human communication there 1st Method was invented By corny and reduce them by the Morse code to wirelessly transmit information from a great For example would mean lowermost cold so it takes a little bit wrong toward transmits a anything Norman Soulliere telegrams were used Would limit the number of words and of course a more expert in Morse code could do it a little bit faster Nowadays would used as a tool of frequency modulation of Carrier frequency and the way this works We have some laugh audio frequency meaning something that can be heard by human beings between 20 and 20 thousand and thinks that with the carrier frequency on radio frequency RF Richard Which is much higher And makes it in such a way that we the told of the carrier frequency The carrier wave is given by Dependence of audio frequency that is 1 possible city or at least slightly changed carrier frequency making Gordon The faster less depending on what we all your And so that's technological Jews Does he Amplitude modulation frequency modulation and then you need soberly in that we can take out we carrier frequency on the Mixed mixed-signal and recover the year resulting this way you can transmit a low-frequency signals as long as the carrier frequency is high enough this has also under
Each the superposition principle for electromagnetic waves offshore us that we can send Uh multiple electromagnetic waves and handles all of superimposed on each other and don't disturb however it If you just started transmitting and receiving waves like crazy said you could separated Any of the messages and so there's a lot of people and you need to be able tools you'd told about particular message that you want receipt for the way this works So you stop solid Michael 4 times the electrical signal and then you have your audio frequency amplified That goes into a mix of you get a a carrier frequency from 1 also simply makes signed and then you have modulated signal which Then the amplified again and transferred 10 and then for the receding on tend to use a resonating circuit and the resonating circuit will only be be effective for Particular carrier frequency so I just need to have an agreement that That nobody else but you don't want you Using the same carrier frequency and you will only then I get A signal of Piedmont that is coming from this particular frequency order A few frequencies around and so usually those Frequencies of purpose frequency bands floats The frequency itself and neighboring free And so after the demodulated you get your audio signal back amplifier You wouldn't want lots and of course TV's transmitted in a similar fashion only that In this case A camera But it was Electrical signals According sole AM stations and a M stands for amplitude modulation 1 of the 2 possibilities for mixing was carrier frequencies Between 500 city and 1 . 7 megahertz Relatively low-cost carrier frequency them FM station BFM stands for frequency modulation was higher frequencies They debate To 108 mega but that's what those numbers on the year Radio button actually means as those of the frequencies for stations that you have to A TV stations in the U.S. use 52 0 2 7 2 Omega A 76 88 174 Wanted said 16 megahertz and 472 698 It's a bomb that A cell phones used 800 megahertz and 1900 About 150 merits for 2 and and more recently also 700 men and other frequencies are reserved for ship playing that police and military communications Even for the radio communication guys this Frequency bands as well as for remote controls that point there's a frequency for everything and they usually are managed by government agencies and if you want of frequency nationwide have to pay a lot of money for the Gorbachev So as an example let's Let's calculate the transmitting wavelength of FM radio stations And the frequencies Given this bonded labor pool somewhere in the middle of the range it stolen electromagnetic waves a speed of light point times the call 8 just a 2nd I can't really hurts and you get wavelength of appalled So we meters is typical of our frequency modulated and A former optimal resonance All fuel I cannot with We signal you want on cannot be about a half away long overweight and so that for that reason FM Montana has about 1 . 5 meters long to get the best resonance amplitude modulation 10 hours I would have to be rather long enough for the same optimization so you can't do do it and we have shorter than quiet I think Europe we all of time and I'll summarize this chapter in the next
Satz <Drucktechnik>
Magnetische Kraft
Schwimmer <Technik>
Natürliche Radioaktivität
Masse <Physik>
Relativistische Mechanik
LUNA <Teilchenbeschleuniger>
Zelle <Mikroelektronik>
Elektromagnetische Welle
Direkte Messung
Römischer Kalender
Spiel <Technik>
Tonsignal <Vermittlungstechnik>
Scheinbare Helligkeit
Galileo <Satellitennavigation>
A6M Zero-Sen
Optisches Spektrum
Scheinbare Helligkeit
GIRL <Weltraumteleskop>
Flüssiger Brennstoff
Wellenreiter <Aerodynamik>
Walken <Textilveredelung>
Elektrisches Signal
Flavour <Elementarteilchen>
Elle <Maßeinheit>
Basis <Elektrotechnik>
GIRL <Weltraumteleskop>
Berg <Bergbau>
TESLA <Teilchenbeschleuniger>
Optisches Spektrum
Kaliber <Walzwerk>
Elektronische Medien
Direkte Messung
Avro Arrow
Fuß <Maßeinheit>
Steven <Schiffbau>


Formale Metadaten

Titel Basic Physics III Lecture 10
Serientitel Basic Physics III
Teil 10
Anzahl der Teile 27
Autor Smy, Michael
Lizenz CC-Namensnennung - Weitergabe unter gleichen Bedingungen 3.0 Unported:
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DOI 10.5446/12946
Herausgeber University of California Irvine (UCI)
Erscheinungsjahr 2013
Sprache Englisch

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Fachgebiet Physik

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