okay so we're gonna start uh the third of four units right so we did uh momentum and then we did fields and forces and now we're doing electromagnetic radiation or this this unit is going to last approximately the same amount of time that fields and forces lasted you have your checklist review booklets you have your Mr reynolds's work booklet the checklist review booklet is is still fairly substantial right um so there's a significant amount of information in there I think a lot of people were surprised how much information was in the fields and Forces Unit but I mean I'm I'm trying to give you as much heads up as possible Julie are there oh uh yep yep okay yeah and then I think I put some extras in the bin at the back but but obviously if you don't get one of those things then just let me know right um okay the first thing that we should talk about is is we should try and figure out like what is electromagnetic radiation now now I when I say electromagnetic radiation I know what I think about but what do you think about when when you hear the words electromagnetic radiation magnet what phone yeah phone phones absolutely most of you most of us have phones on us at this point in time right are the phones giving and receiving electromagnetic radiation yes 100% they are what form of electromagnetic radiation are the giving and receiving I don't know somebody's saying it I'm not hearing it radio waves yeah hell yeah now that's I mean that's the type of electromagnetic radiation that they're using in order to communicate right so uh electromagnetic radiation we're going to abbreviate it as EMR electromagnetic radiation EMR they are oscillating Electric [Music] and magnetic fields uhoh they're oscillating meaning some sort of repeating pattern right up down up down up down up down up down of electric fields and magnetic fields at the exact same time so what we're going to think about here for a second is uh uh I just want us to I'm going to draw something uh but I don't really want us to draw a diagram of it because it's just really us kind of exploring what's G to happen Okay so imagine I had a positively charged particle and then I had way over here another positively charged particle so don't don't draw this we're just kind of trying to to figure it out we're trying to kind of map out what we mean by electromagnetic radiation okay so uh we know based on the unit that we just did that this is a point charge right it's a charge and it's it's giving off a what it's giving off an electric field there's an electric field all in every point in space surrounding this positive charge there is an electric field right so for example right here where's the electric field pointing that's coming from that thing yeah it's going away from it okay good that's awesome um and so this thing is giving off an electric field here we have another charge this charge is sitting in this charge's electric field would you agree it's sitting inside the electric field that's being generated by that charge so because it's a charge sitting in electric field it will feel a force applied to it okay so what direction will the force be applied in this particular situation where is this charge going to feel a force it's not a trick question what direction will the force yeah perfect so that'll be the force so but let's think about this for a second uh imagine these charges weren't just sitting in open space they were like part of materials and so these charges can't really they're not like super crazy mobile okay this thing pushes on that thing as far as it'll go but as long as they're just kind of staying there would you agree they'll they'll kind of they'll reach an equilibrium position where they're pushing pushing on each other but they're not really doing anything they're not moving around are we okay with that okay so what I'm gonna do is I'm I'm gonna change this situation I'm gonna take this positive charge and I'm going to lift it up now what effect is that going to have on this particle it's going to change the direction that the force is being felt on that other particle instead of the force being felt like that what direction is the force going to be felt kind of down into the right a little bit so remember that that charge was already pushing this charge as far to the right as possible so it wasn't going to go any further to the right but now that we've picked up that charge this charge can't go any further to the right we've already established that it's reached an equilibrium position it's not going to go any further to the right but what direction can it kind of go down by lifting that particle up we can cause some motion down is that okay so it's going to move down a little bit okay now if I take that particle and instead of instead of going up what if I went down what would happen to that particle it would go up but how they're not touching each other how is the force on this thing changing what's changing first the direction of the electric field does that make sense the two interact with each other through an electric field and so uh I'm going to show you a video and the video hopefully it's not like you know it's a lot I'm not going to lie to you it's it's a lot but hopefully we we kind of uh get a little bit out of this video okay [Music] okay so we have the exact same situation here we got a positive charge there we got a positive charge there and right now it's sitting still so in order to cause it to go up it has to accelerate would you agree it's sitting still right now it's at rest in order to start moving it has to accelerate and so this thing is going to accelerate when it starts to accelerate like right now now the electric field at this point right there is going that way but as it accelerates up the electric field will start to point that way are we okay with that now what I want to be really clear about is they're still mostly pointing right but what what direction have we now introduced into the electric field what's the change in the electric field if they're still going right but what's the new Direction we've introduced down so at the electric field was always going right but now it's going kind of down more than it was before is that okay okay so let's keep going and how it was accelerating at this time zero after a certain delay this causes [Music] don't freak out you are never ever ever going to use that unless you go into electrical engineering okay so we're just going to back up a little bit just G to back up a little bit it's okay it's okay so when this particle accelerates upwards it causes a changing electric field that is mostly pointing down right so let's see that changing electric field it's the change in the electric field that we care about okay so let's see the change in the electric field propagate towards that other [Music] particle did the electric field when we moved that charge up when we accelerated it up did this particle immediately feel a change in force no it's G to take a certain amount of time in order for the change this is almost like a this is a uh like what word we would would we describe to cause this uh it's a wave whoa that's amazing you've got a wave it's propagating this way hey how fast is this wave propagating this changing electric field how fast is it propagating a at a speed at the speed of light this this right here this changing electric field is quite literally the definition of what light is when you're interacting with light you're interacting with changing electric and there for magnetic fields because we know that every time we have something electric happening typically we have something magnetic happening at the same time we know the two are are linked together and so uh anyways let's just keep doing what we're doing Z after a certain delay this causes a force on the second and the equation describing the force looks something like this so again it's proportional to the charge of both of the particles and once more common way to write it [Music] inv okay okay anyways so now now we not only have a single charged particle we've got a group of charged particles because matter often isn't just a single particle matter is often a group of charged particles right you have a group of nuclei or you have a group of electrons okay and so what we're going to see happen happening is is well what if we oscillated what if we what if we caused some continually accelerating charged particles to go up and down up and down up and down you know if they're going up in order to cause them to start going down they need to accelerate if they're going down in order to cause them to go up they need to accelerate and so when you have Al oscillating particles those oscillating particles are constantly accelerating is that okay they're either accelerating up or they're accelerating down and they're accelerating in in uh uh changing fashion Okay so we've got a group of charged particles and they're going to go up and down up and down up and down and we're going to see the changing electric field that propagates um away from them this component of thec the effects of all these purges interfere DEC constructively along the Y Direction but they interfere constructively along the X Direction this is what it looks like for a beam of light to be concentrated along just one dimension so if you were to focus on the field just along the xais instead of to [Music] this okay so this is what when you have oscillating charge particles those oscillating charge particles are going to create a changing electric field and the changing electric Fields is also going to oscillate up and down up and down up and down so we get a wave of oscillating electric fields and we know that electric fields and magnetic components remember electric and magnetic components are often at like 90 degrees to each other okay so you will also have a magnetic component and we'll draw that in here in a little bit but that's this is essentially what light is and light the type of light you're looking at visible light x-rays gamma rays radio waves microwaves really just depends on how fast are these particles oscillating are they oscillating really quickly or are they oscillating quite slowly and they'll give off different types of electromagnetic radiation and so we've got a we've got aop oh man it's over here sorry I'm probably gonna have to reset it bam yep okay woo so what we have here is we got a really long wire and we can cause the electrons inside the wire we're only looking at one electron but we can we can look at a bunch of electrons or think of what's happening when a bunch of them H uh do the same thing okay so uh remember when I when I take this electron and if I accelerate it up when I accelerate it I'm going to change an electric field so that change in electric field is going to propagate away from this humongous wire right so if I take this and I pull it up for example you see that electric field propagating oh let's try it again do you see it whoa now I'm I'm crap at this so let's let a computer do it because what we're doing is we're trying to hit the resonant frequency of the electrons in this wire over here we're trying to cause a standing wave and we know that standing waves from physics 20 only happen at certain frequencies and so I'm not I'm not good enough to be able to cause a standing wave happen but what I can do is I can I can let the computer do it for me o there we go hey what is this building that is causing these oscillating charges and they're that's propagating this wave of electromagnetic radiation and then it then it goes all the way to this other building this other building has a wire and that wire picks up the change electric field and then it it oscillates at kind of the same frequency what what's this building over here it's a radio station it's sending off radio waves and this is your car or your house or your radio and it's picking up those radio waves so all that really matters is that are the oscillations over here are they sending off a changing electric field that your wire in your antenna can pick up does that make sense so we our first kind of a couple things that we have to do is we have to draw a picture of electromagnetic radiation it's G to suck but you know whatever uh it is what it is I suppose okay so I'm gonna I'm gonna get rid of this okay so this is the anatomy of electromagnetic radiation uh essentially what we have going on here is is we've got I I'm going to draw like an equilibrium point I'm going to draw a straight line so that we have some sort of a reference and so what's happening is uh you're going to have some accelerating charge particles and they're going to cause a changing electric field in One Direction so we're going to have a wave of changing electric field and I'm trying my best to make them very evenly spaced I don't know how well I did how good of a job I did so this is like our this is our electric field or our changing electric field it's going to oscillate back and forth between up and down up and down up and down up and down and the waves propagate out into space now remember whenever we have some sort of changing electric something or other then often we induce a changing magnetic something or other and so if the electric field is oriented upwards if the propagation is this way but the electric field is oriented upwards then where's the magnetic field it's horizontal now this is going to be kind of difficult for us to draw um I'll show you a picture of kind of the anatomy of electromagnetic radiation okay so this is what we're this is what we're g to try to draw this is don't freak out it'll be okay okay so hey can we see that changing electric field the electric Fields upy Downy right and then the magnetic field the magnetic field is in oute is that okay okay all right we can do this I have faith okay so this is the way that at uh I'm garbage at perspective but you know we'll see how it goes whoa whoa whoa whoa whoops and it's kind it's kind of going left and right left and right left and right woo okay so what's important about this is that if the wave is propagating forward then the electric and magnetic fields are both 90 degrees to the propagation so both e and B are 90 degrees or perpendicular right perpendicular to the propagation of the wave so the waves traveling that way but e and B are traveling 90 Dees to the propagation it's going this way e and B are that way I'll put up that other picture because obviously it's better than mine but and then you can compare your Artistry to my Artistry and feel free to mock me that's totally fine I have no problem with that biologists are supposed to be good at drawing nobody said nobody ever said chemists and physicists had to be good at drawing okay so I just just to put that back up there okay that's what we're trying to draw the propagation of the wave and then the electric and magnetic fields are oscillating and remember it's a change in we care about the change in in electric and magnetic field that's really what we care about okay now electromagnetic radiation was first kind of hypothesized by uh a guy named James Clark Maxwell and if you ever go on to do electrical engineering or if you go on to do uh some sort of electricity and magnetism courses at the University level you will you will Ru the day or you will I don't know cheer the day you heard Maxwell's names so James Clark Maxwell pretty predicted kind of five things about EMR the first thing the first prediction in all five things uh became true but you know whatever um so the first thing that he predicted is that is that EMR is created or produced whenever charged particles accelerate they create electromagnetic radiation whenever they accelerate because when you accelerate you change the electric and Fields the second prediction that he made was that the frequency of EMR generated will match the frequency of oscillating charge particles the frequency of electromagnetic radiation generated will match the frequency of oscillated charge particles so if you have oscillating charge particles if they're vibrating let's say a million times a second then you're going to generate light that has a frequency of a million oscillations per second now there are some equations that go along with this there's a really important word frequency you know a little bit about frequency frequency of any oscillating or rep repetitious uh pattern the frequency is related to one over the period do you remember doing this in physics 20 where f is frequency I don't know if you remember what frequency is measured in but we're going to circle back to it okay T is period so remember period is how long does it take for one oscillation so that's the time for one either oscillation oscillation or repetition depends on the way you want to think about it so I want to be really clear period is time right what's time often measured in seconds good so you could say it's seconds per cycle or often we just say seconds because we're referring to how much time does it take to do one cycle or one oscillation or one repetition are we okay with that oscillation repetition and cycle all mean the same thing a repetitive process and we're referring to one complete repetitive process okay so if period is measured in seconds or seconds per cycle then what's frequency measured in yeah okay so there there goes your your your memorized brain comes into perspective right you said hurts but I don't I don't want hurts right now what is it actually what Chris good Cycles per second so frequency is measured in it's just it's the inverse of it right if if we you take one divided t one divided by cycles per second well you just flip it it's being measured in cycles per second or one over seconds because we're we're just saying like we always assume it's one one cycle or one repetition or one oscillation how do you write one over s what's another way of writing one/ s you could go s to the 1 that means one/ s or we Define one Hertz to be one repetition for per second I know that sucks I know it really sucks to be able to see the units for frequency being represented in so many different ways but what's important is that Hertz equals one over seconds if you want frequency where do you want seconds to be on top or on bottom on the bottom that's the important thing to know if you want frequency you need seconds on the bottom if you want period you need seconds on top are we okay with that that's the that's the idea behind it okay doy so James Clark Maxwell predicted five things electromagnetic radiation is created whenever charge particles accelerate the frequency of the electromagnetic radiation generated will match the frequency of the oscillated charged particles so if you know how much time it takes for the charged particles to complete one repetition right then you can calculate the frequency so you can predict the type of electromagnetic radiation that will be generated number three that's the wrong color since electromagnetic radiation is just oscillating electric and magnetic fields all EMR travels or propagates is that how you spell travel there's one Len travels come on Walton travels at the same speed we Define we Define the speed of light in a vacuum we Define the speed of light in a vacuum to be the letter c and we say that it is 3.00 * 10 8 m/s that's on your formula sheet you don't have to memorize that that's always going to be there okay so lights a wave it's oscillating electric and magnetic fields that are propagating in a certain direction well we know that waves all waves follow the universal wave equation what's the universal wave equation again uh oh what's the universal wave equation again where V is the speed of the wave in our case What wave are we talking about we're talking about the speed of light right so anytime you have electromagnetic radiation you know it moves or propagates at the speed of light as far as we're concerned in a vacuum okay F again is frequency measure in hertz or cycles per second and what the hell is this thing what first of all what letter is that that's Lambda right sorry what does it mean it means the wavelength we want wavelength wavelength is a length what should length be measured in meters love it fantastic so when you take meters and you multiply by one over seconds you get meters per second so okay yeah our speed should be measured in meters per second okay so I I want to be really clear because we're this there sometimes are kind of interesting problems that that involve you to go into kind of nitty-gritty detail about this okay so uh wavelength yes that is the wavelength how do you determine wavelength well if we had if we [Music] had okay so here's a wave how would you define wavelength so the length from Crest to Crest right that's a wavelength is that the only way you can define wavelength any two points along this wave that are identical to each other so Crest to Crest good trough to trough that's totally fine what about here to here midpoint to midpoint no midpoint on the way down the next uh the one wavelength over would be midpoint on the way down we say that these points are in Phase with each other fantastic so uh uh points that are in Phase with each other are multiples of a wavelength apart from each other good so wavelength right is just the length we say from Crest to Crest but that's not the only way to do it okay three out of five done so far moving on to number four I know that this sucks but you can deal with it with the beginning of every unit is always vocabulary heavy would you agree yeah always yeah we have to go up to five we're only at three that's okay the next one's uh the next one's easy okay so he made the prediction that b and e not breaking and entering B and E oscillate we already talked about this but they oscillate perpendicular to each other and perpendicular to it's a propagation propagation that's not how you spell propagation propagation wh don't know how to spell propagation of the width okay and then the very last one and this is where you get to kind of think a little bit EMR because it's a wave it shares properties of other waves so other transverse waves because it's a transverse wave so what types of properties do waves do what kind of what kind of things can waves do they oscillate okay but what can they do yeah oh that's so good that's awesome they can perform how do you spell interference C sure C interference they can interfere with each other either constructively or destructively perfect so good right when two crests meet each other they amplify each other they add to each other constructively okay what else can waves do it's just been a it's been a while since you've talked about this and I I totally get it I completely understand they can undergo waves can bounce off of things right echo echo echo echo good okay so they can bounce off of objects well if they can reflect then they can it's okay if you don't know what refraction is that's totally fine we're going to talk about that they can also undergo and then the last one and that's okay it's totally totally totally fine if you don't know what most of these things are we're going to talk about every single one of these in due time okay so one of the last things I want to talk about uh before we do like a little bit of work is I want to talk about the electromagnetic spectrum okay so you have maybe drawn this picture before I'm going to go to a new page I'm just burning through digital paper here whoa cutting down digital trees ah the EMR Spectrum so what we're going to do is we're going to uh electromagnetic radiation is defined by how fast they oscillate another way they're defined by is is by how tightly packed the waves are okay so what do you want to talk about first do you want to talk about really tightly packed waves or do you want to talk about really stretched out waves stretched out waves largest wavelengths okay so we're talking waves that are really stretched out and then we're going to work our way towards shortest wavelength and that's like like waves that are like this but even more extreme so there's different types of electromagnetic radiation out there um which one do you think has the longest wavelength which one do you think is the most stretched out what what types of electromagnetic radiation exist out there we''ve already talked about a few radio waves what if you're saying something what was that Hunter gamma rays radio waves gamma rays light ultraviolet microwaves infrared xrays boom we've hit all seven is that seven one two three four five six seven fantastic okay uh I'm curious does anybody know which one has the longest wavelength radio radio to Canada okay so radio waves have the longest uh they have the longest uh wavelength uh okay so what's what's a little bit more compact what's a little bit shorter wavelength than radio waves when you go from radio waves you go a little bit higher energy than that you're going to get to good so we go from radio waves to microwaves okay and then from microwaves you a little bit faster a little bit shorter wavelength okay what's a little bit more than microwaves good we're going to go infrared radiation okay and then oo what are we starting to butt up against Infrareds right beside visible visible light okay and then visible light well if Red's on the one side what's on the other side oh yeah ultraviolet right they're referencing what part of the visible spectrum their right beside okay and then we got go a little bit shorter than the ultraviolet what are we going to get up next to oh we're going to get xrays first and then there's there's a real kind of it's not quite clearly defined where xrays end and gamma rays begin but we're going to Define gamma rays to be a little bit shorter than that now I alluded to it already I alluded to it already um but uh radio waves are radio waves really high energy are they melt your face off radiation or are they pretty low energy they're pretty low energy the longer the wavelength is think about it this way uh if you were out on the ocean and you and you saw some really long not tall really long waves coming towards you would be you be particularly worried about that because your boat would go uh up and then down it'd be really gentle not very high energy but if you came across waves like this right where you were gonna get wave wave wave wave wave wave wave right that's you going up down up down up down up down that's really high energy waves that's one way to think about it okay so so the long largest or the longest wavelengths all the way to the shortest wavelengths we can also do the exact same thing with energy we're not going to rewrite all the things but radio waves are lowest energy okay so what's the highest energy electromagnetic radiation out there gamma rays perfect highest energy but we can also talk about it in terms of frequency do radio waves or gamma rays which ones are oscillating more every second the gamma rays are oscillating more every single second remember the waves are traveling at the same speed so if if one is really stretched out that means you're getting fewer waves every second more waves every second so this is also [Music] lowest frequency and this is highest frequency so frequency is directly proportional to the energy of a wave the more Waves per second the more energy is is is striking a surface or something like that okay now there is we do have to memorize a little bit of information let's specifically talk about visible light okay what do you want to go do you want to go uh red to Violet or do you want to go Violet to red red to Violet okay no problem so red what's next orang Orange what's next yellow there you go what's next Green what's next Blue what's next Indigo doesn't exist Violet perfect Roy G so we've got the visible spectrum here fantastic and what I want to be very clear of is that is that on this side is infrared [Laughter] and on this side is ultra violet now where red begins uh which one of these two colors red versus Violet which one of these two colors is longer than the other red red light is longer so does that mean it's higher energy or lower energy lower energy does that mean it's higher frequency or lower frequency it's lower frequency good so because it's longer um we're gonna kind of Define this isn't really a hard and fast rule but we're going to make it a hard and fast rule so we're going to say that the barrier between infrared and red is [Music] 750 nanometers and we're going to say that the barrier between Violet Violet and UltraViolet is should it be longer or shorter shorter so 400 nanometers you do have to memorize that it's going to be helpful to you so what I want you to do is I want you to convert the longest visible wavelength into frequency I want you to get the frequency of the longest visible wavelength that we can have I'm going to give you a couple minutes to try that out you got to talk to somebody go ahead and talk to somebody you're going to have to refer back to some stuff that we already talked about get the frequency for the longest visible wavelength h e T I'm G to give you 30 seconds to finish up and then we're going to go through this [Music] okay sorry what do we want we want frequency okay so what I'm going to do is I'm going to look for frequency hey do you see any formulas that have frequency on them right there two formulas have frequency in them right hey there's frequency related to period do they give do they give us the period the amount of time it takes for for the longest visible wavelength to oscillate no they don't give us the period Shak so that one's out uh okay so we want frequency could we use this one do we have the speed of this particular wave what type of wave are we talking about we're talking about visible lights do we know speed of light hell yeah you do okay so you want the frequency okay we have the speed of light it's C but we'll write V uh hey do you know the wavelength for the longest wavelength of visible light yes you do what is the longest wavelength of visible light 750 nanometers oky doie so let's go ahead and try this out so V equals f * wavelength but we want F so we're going to divide by wavelength so frequency is speed divided by wavelength I know both of these speed of light 3 * 10 8 m/s and then the wavelength is 750 nanometers but I don't like nanometers what am I going to change that to time 10 9 m perfect we take that and we uh toss it into our calculator and we should get what do you get four time 10 14 Hertz yeah four time 10^ 14 and our unit is Herz because Herz is frequency now what does that mean like what does this actually physically mean what's frequency again it's how many Cycles in every second so red light remember the one that's the one that's oscillating less times per second how many times per second is red light going up and down four time 10 14 I don't know if you need a recap of scientific notation but how many times per second is that that's 1 2 3 4 5 6 7 8 9 10 11 12 13 14 times per second so something something giving off red light has charged particles inside of it that are going up and down up and down up and down this many times per second we're starting to get into the realm of like it's hard for us to understand even what's going on because this number is so large it's it's kind of not really comprehensible for our brain okay so I want to warn you there will be times in the next two and a half months where you say but why does that happen and I'll say you don't get to answer ask that question or you do get to ask that question and I I just get to tell you because it does and we move on okay shuy Doodles that's right Paro shuy Doodles okay hey I got a new question for you how much time does it take for the longest oh my God for the shortest wavelength visible light to oscillate how much time does it take for the shortest wavelength of visible light to oscillate how much time does it take for it to be able to some people are doing it and that's awesome but does somebody want to share me their game plan okay good so we want what do we what do we want of this how much time but what is that like how much time for a complete oscillation what what what is that definition period we want period right so okay we're asking ourselves for a period whoa didn't mean to do that there's only really one place to get period we're not talking about a pendulum or a spring system or something like that so periods related to frequency so what do you got to get first frequency how do you get frequency from the speed of light and the wavelength of the W so it's a two-step problem number one same thing as before try and get the frequency so three * 10 8 m/s and then it's 400 nanometers so I get 7.5 * 10 14 Hertz and so now now that you have frequency in order to get period it's just the inverse of frequency so 1 over 7.5 * 10^ 14 Hertz do you remember which button on your calculator does this x to the^ of1 right you could go one over this or you could just go x to the 1 this is what I get I get 1.3 * 10 -15 seconds casual reminder so that's a 0 point 0.0 zero dot dot dot dot dot zero and then it'll be 13 repeating and in here there's going to be 14 zeros that's how much time it takes to be able to complete one oscillation for a violet light or or or really shortwave violet light are we okay with that okay I am so sorry about this okay I know that this has been like a long day so I want you to do some of Mr Reynold's questions I know tomorrow we're going to talk about how to measure the speed of light so this is section A and I want you to do one [Applause] to eight and nine that's all I want you to do right now 128 N I really don't think it's going to take a ton of time for you to get through at least three of these questions so try it out