welcome so in this video we're going to talk about light and some of its properties and we're going to calculate some of those properties such as energy and frequency all right so um light is made up of particles I have to put that in quotes uh particles uh called photons and the reason why I have to put particle in quotes is because light uh photons also have this uh wave nature okay all right so maybe for another time we can talk more about whether light or any of the observable universe whether we are particles or we're waves okay the short answer is we're a little bit of both but when it comes to photons this wave Nature has to be uh discussed as we're going to see photons have a property called wavelength and we're going to have to use that wavelength to calcul at uh other useful things such as frequency or energy and wavelength itself is um an important quantity all right so photons have all these sorts of properties uh energy frequency wavelength speed all of these are related to each other um in equations um amplitude uh we're not going to discuss so much of that today uh if you have more amplitude that just means you have more photons um and useful to know not going to talk about it a ton but useful to know photons don't have any Mass they are truly massless it's not like we're talking about an electron which it has a very small Mass but technically it has a mass photons have absolutely zero Mass any particle of light has no mass at all right and there's no charge either it's not like we're talking about protons or electrons um that have charge uh there's no charge involved all right so photons are light also known as electromagnetic radiation all right now don't confuse this word radiation for talking about like radioactivity when you have a radioactive material that means that material in the process of transforming is releasing actual um particles okay uh protons uh or excuse me um alpha particles man quot recording lat at night will make your brain freeze but um alpha particles beta particles I mean you can have high energy photons called gamma rays but uh that's coming from a material that's transformed here we're just talking about um photons not radioactive materials all right so with that little rant out of the way I mean explanation um all right so we got um some light equations to uh discuss all right uh pause this for a minute if you want to um soak it all in write down some notes Let Me shrink my face here there we go all right so there's three uh main equations that are in a typical chemistry 101 course all right um and you could even say these two equations are the main ones because uh you can substitute this equation into that one and you can end up with this one if if you were to want to do that uh you would rearrange this equation for uh this symbol I circled in blue all right it's called new You' substitute that in and then you would get this equation all right but we got three equations we have uh energy versus frequency energy versus wavelength and then we have the speed of light relationship all right so let's go through each of the letters or uh symbols for first e stands for energy and energy when you use these equations with these constants those are going to be in units of the energies will be in units of jewels all right then we have something called frequency frequency uses this Greek letter called new it looks a lot like a v um but it's a new I'll show you how to write it in a moment um and frequency is how many times something happens in some period of time and in these equations that period of time is going to be a second frequency is not in seconds seconds is time itself whereas frequency is how many times something happens in one second all right so a little bit of a difference that that second is in the numer uh denominator the bottom all right so 1 over seconds for frequency you can write it that way s to the minus one power or or you can write it as a unit Hertz me personally I usually do that but you do your thing lastly in these equations we have wavelength and that's the Greek letter Lambda all right another thing we'll have to learn how to write and Lambda um wavelength you're going to use units of meters all right now I did write this little note here that forgetting this the most common error sometimes the wavelengths are given to you in a different unit uh most commonly nanometers when we're talking about visible light all right so if they give you something in nanometers in order to use these equations you'll have to convert it to meters first if you were given something else like an energy or frequency you're trying to calculate a wavelength they might ask you for it in nanometers so you would take your meters answer and then you would turn a nanometer so I'll show a little bit of that um in the example today all right the last two things I didn't point out yet this is called plon constant a lowercase H 6. 626 * 10us 34th power and then there's two units Jewels the energy unit we talked about earlier and then we have seconds all right it's Jewels times seconds for the units all right and then the other constant is the speed of light constant um all photons travel the same speed regardless of their energy all photons travel the same speed and that speed is 3.00 * 10 8 power m per second all right um if you were to measure or calculate how long it takes a photon to go from one end of the Earth to the other it's like less than half a second um last time I calculated hopefully I still remember that correctly um youall Can fact check me on that you want all right um and some people will uh sometimes use like the more accurate precise version of it um I like to write 3.0 for my oneone classes because for me having a number people can remember and still be accurate with uh is uh the higher priority for me but 2998 uh is also fine here all right so I promis some handwriting lessons well I don't know if my handwriting is a w winning or anything like that uh but um how do you write a new all right so um I like to write my new like that all right it doesn't always come out the same um sometimes you'll see like a little bit like that um but that's a new whereas that's a V all right if one of my students started writing V's instead of news would I really care me not really all right but I'm not I'm I may or may not be your Chemistry instructor whoever depending on who's watching this um and then we have Lambda or Lambda all right it kind of reminds me of a wave it looks kind of like wavy right um all right that's how I write my lambas or sometimes I just kind of go like that all right um something like that and that's what we use uh for wavelength all right so there we go all right so we're about to get to our example problem but first I thought I'd give um some description of what these Photon properties mean I use words like wavelength frequency and what do these things actually mean all right and I think to help explain it I'm going to do comparison between between a red Photon and a violet Photon all right so the first thing I'm going to tell you is that a red Photon I mean there's different shades of red that exist but a red Photon this particular red Photon um you can get it from like a red laser pointer or something um has a wavelength for this particular shade at 650 nanm and then for the Violet Photon you can sometimes get these violet or sometimes they called like purple um laser pointers and uh 405 nanom all right so whatever this wavelength is for Violet it's shorter compared to the red all right wavelength is a really fundamental property of light of photons uh it's that wavelength that tells you um what type of photon it is and if we're talking about wavelengths in the visible spectrum of light the photons you can actually um see then um they're they're going to have different wavelengths for different colors all right and um to kind of give a preview for the last part of the talk all right there's this whole um electromagnetic spectrum all right from low energy to high energy and within this small sliver I may be made it too wide but within this small sliver um you also have an energy ranking for the uh visible colors uh Roy G Biv red orange yellow green blue indigo violet all right so said in another way a violet Photon has a higher energy and therefore a higher frequency and therefore a shorter wavelength compared to a red Photon all right and this is something that's good to remember but I like to bring things back to math when possible that's something you can see within the mathematical equations you can see if you raise the frequency the energy goes up too if you uh raise the wavelength make it um longer you can see how that lowers the energy if you make a wavelength smaller you can see how that will increase the energy because a smaller denominator means a bigger number on the other side all right and then with the speed of light relationship you can see that for a photon if you raise its wavelength you automatically also lower the frequency all right and vice versa all right so in this equation energy and frequency have a direct relationship they move in the same direction here we have a inverse relationship energy and uh wavelength go in opposite directions and the same can be said for um frequency and wavelength all right what helps me remember all this even in case my brain's not speaking math well that day is I always remember energy and frequency going the same direction but then wavelength doesn't okay this is the most simple looking equation at least to me so I always start with uh that all right but at the end of the day that would come out in any calculation anyway so I'll leave it to you whether to consider memorizing those relationships or not okay all right but back to defining uh these uh ideas of frequency um wavelength and stuff so what I did was I drew um wave models for a a red Photon versus a violet Photon all right um and these Photon wavelengths can be thought of as like s functions all right like s uh cosine you know do the wave thing right okay and so what is that wave all right um I'm going to try to give an explanation at the chem one1 level it's not necessarily the most I hate to admit it the most important thing to uh know but uh I mean it's somewhat yeah well I'll let you judge that all right so photons have have um a property called having an electromagnetic field all right so even though photons don't have charge they have um electromagnetic field going on just like as if they did have charge all right and so uh the photon okay we draw it like a wave but um in reality that wave is actually um just measuring the strength of its electromagnetic field which means it's ability to interact with a charge okay it's just measuring its electromagnetic field at any given point in time so you can see right here that's the strongest part of the electromagnetic field in this moment all right as it has traveled that much it has the most strength there and then it reaches a nothing point and then here it's the equal strength but um opposite uh equal but opposite all right and this sign Behavior this wave behavior for the electromagnetic field strength uh carries on until the photon is uh absorbed um somewhere all right the main point especially at the ch11 level is to just observe that this wave property is longer for a red Photon compared to a violet Photon that's honestly uh the most important thing to recog recognize here so you can see that kind of Drew out here one complete wave and it's got to be complete you got to go through the positive and the negative part of the amplitude Okay um amplitude just how much it's sticking up fancy word for how much you're sticking up right you have to go through one complete cycle and our wave length is from there to there okay and of course this isn't actually 650 nanometers I just magnified it all right um but yeah we could just pretend this is 650 NM all right whereas for a violet Photon that wavelength is shorter it's 405 nanometers I prefer to um if I was asked to point out one complete wavelength for a photon I prefer to go from starting at the bar um the the x axis I should say and going like that and that's what I did there so I get like a clear positive and negative for the amplitude uh for some people they find it easier to start from the crest of the wave and then go to another Crest and then call that one wavelength all right it doesn't matter because mathematically it's the same distance anyways all right so you just do whatever makes sense for you all right so with some calculations um we can um figure out uh these other properties for um the photons all right so um we're going to calculate for the red Photon today we're going to calculate uh its frequency we're also going to calculate its energy all right but before you do that you're like what's frequency you didn't do that yet okay um so I don't know if you caught on to this okay I was giving your brain some time to see this first as I was talking but from here to there or heck we can just go to the end of the page from here to there versus here to there I want you to notice that the red Photon oscillated less times compared to the Violet Photon all right like on this page the red Photon oscillated maybe about one and a half times all right and then for the Violet Photon one two like two and a quarter almost all right so that's what frequency means it means the number of times your electromagnetic field has oscillated in 1 second all right uh so we can see the Violet photon is oscillating more all right so the Violet Photon will have a higher energy and the way I tell my students to remember that higher frequency means higher energy is this may sound silly but I just have them uh wave their hand and you wave your hand faster a higher frequency of waving that takes more energy for you to do all right so if you're at an exam and you're doing that uh hopefully people uh I I guess you can't talk an exam but if you could you just tell them oh I'm just remembering a frequency all right so let's um calculate for a violet Photon and for some of you they'll probably be enough an example um and then we'll do the red Photon um afterwards for a comparison all right so uh yeah let's do it let's calculate the energy and frequency of a 405 nanometer Violet Photon okay so we can do this in any um order the first thing I like to do is I like to write out all the equations involved in light all right and depending on your class or your instructor you may or may not have to memorize these okay um so we're first looking for an energy let's get energy first so um that narrow it down to these two and we were given a wavelength okay so that means this one is not going to be used uh for this problem right I'm going to use this equation because I can put in a wavelength and get out an energy of course uh our luck is this is the most bulky looking equation um but that makes for a good educational um example we'll do that frequency a second right so let's calculate energy we're going to um put in a wavelength and we're going to get out an energy all right here we go so this equation is perfectly ready to go actually because we are wanting the energy um we don't have to rearrange it for the wavelength so we're just going to be doing some plug and chug all right now sometimes when I'm teaching this like live uh I have us set up the math and then run into the speed bump um and then correct it but um I'm going to take a different approach this time I'm going to address the speed bump immediately okay recall earlier that I said we might need to use this piece of information okay notice that we were given a wavelength in nanometers again very common for visible light but these constants um the speed of light works in meters in order to have correct unit cancellation we're going to have to convert this to meters all right so let's do that immediately okay I'll write out my steps first convert nanometers to meters I'll do some dimensional analysis there are 10 to 9 nanom in 1 meter okay that's three sigfigs we have infinite sigfigs on a conversion factor so we're going to have a three SigFig answer like I've said in other videos number of sigfigs in is often equal to the number of sigfigs out and this is no exception okay now um I can do this in my head but I'll just show the key strokes all right I want scientific notation here all right 4. 05 time 10 to the uh -7 M okay all right um that's not the energy yet we are just doing the busy work of converting we haven't even done the actual problem yet all right next paper Okay so we're still doing wave L to energy there we go and now we want to actually use the equation so second we're going to do plug and chug all right so here's our equation and showing your work is not going to be really fun here CU we have two long constants to write out out so we got 6. 626 * 10 karat - 34 Jew seconds that's our plunks constant H then we're going to multiply that by the speed of light all right and then let's get our denominator so we did the work earlier we got 4.05 time 10 to the - 7 m all right hopefully you had a lot of fun writing that out anywh who so let's keep track of our unit okay so energy is going to be in Jewels right so we're hoping that Jewels survives all the unit cancellation going on all right our meters and our meters cancel out because meters over meters is one so that factors out and then we have seconds times 1 over seconds all right seconds divide by seconds so those cancel out as well all right right and the only units that survived the unit apocalypse was the jewels all right so I'm just going to write my Jewels there as my unit before I forget and now we can punch into the calculator all right let's see all right and I'm still in scientific mode so I got that nice power of 10 that power of 10 is so extreme that it would be a power of 10 in this calculator even without scientific mode um but anyway so I get 4.9 round that up to 1 * 10 to the -9 jewles all right 4.91 * 10us 19 Jew and that is our answer for energy okay typically chem one one class I am guessing most instructors will just have you leave it in Jewels um there is a unit that exists that uh is smaller than Jewels so you don't have to write out all these like really dinky powers of 10 it's called the electron volt but um I got to keep my class simple so I just I got to hold my tongue and not reveal that all right uh but we're not done yet because the problem also wanted uh so energy and then a frequency as well all right so those two so did energy now let's go back to our menu of equations we had eal H new we had e = HC over Lambda and then we had Cal Lambda new all right so we're looking for a frequency this time we're looking for that one all right so that eliminates that from the menu and we got two choices we could use this or we could use this all right so either would work uh in a tip breaking situation you can just consider what you enjoy doing more um I'm going to go uh in a different direction though I prefer to use the equation where I can use um as much of my original data as possible like if I already used this equation that'd be okay um there's the energy I can um plug that in solve for the new um but like this is already um like a calculation that wasn't originally provided whereas this equation um I can just use uh the Lambda that was already provided and it's you've lowered your risk maybe a tiny bit in case you made like an error here um it wouldn't like propagate again all right um either way uh in fact uh I could show it both ways I'll start with this one um if you're satisfied you can just leave the video at that point um or skip to my final comments um but I'll show that one as well I have a feeling someone will want that as well okay all right so we're getting frequencies we're going to um use this equation and I'm going to rearrange it by dividing lamb on both sides so I end up with um new = to C over Lambda all right all right cool I think uh we can do this so um in other words we're putting in a Lambda and getting out a new okay all right so I'll just rewrite that equation speed of light C is 3.00 * 10 to the 8 power m/ second and we're going to divide that by um the Lambda that we found uh earlier now um don't put in nanometer one because that won't cancel properly so we have to put in the one we uh converted earlier that one okay so we can plug that into the calculator I always use parentheses for for my denominator okay those who have been with me a while know that if this is your first time watching me um I'll just tell you of that all right so uh there's the answer 7.4 1 * 10 the positive 14 um inverse seconds per seconds Hertz whatever you want to call it and that is our frequency all right so in a span of 1 second we had our electromagnetic field okay wave pulse whatever you want to call it 7.41 * 10 to the 14th power times okay that is a lot of times of it fluctuating all right in just one second okay um an alternative approach uh you know I've shown a lot of dimensional analysis in previous videos so maybe you'd prefer that approach over uh this algebraic approach okay if you're going to go that way you start with um actually this number okay so I'm just going to write alternate dimensional analysis approach when you do dimensional analysis you always start with whatever has a single unit um almost always um so what I would have done here I'll just go to a different color you just go 4.05 * 10-7 M and then we need the meters uh here and the seconds there so that number is Tethered to the meters so we go like that per 1 second you can see our meters cancel leaving up with seconds all right and then we would uh I don't like what I did here um I should probably at the edit this out but then again I'm just going to leave in the video just um I think it's sometimes good to people see that um I make mistakes sometimes too when I'm getting here well I might as well finish the Trap I set up for myself um all right so I got that number that's a -5 and that's seconds um so what I realized Midway through is um I should have had that at the bottom which is a little bit unusual but maybe now you can see why I ended up with seconds instead of inverse seconds all right so what we could have done instead we could have started with the bottom or we can just realize that frequency is going to be um one over seconds so we can just do 1 divided by the answer okay which is the same as doing the inverse function the answer I'll just do answer to the minus one power and then we got the same thing as last time all right um so I am definitely a fan of dimensional analysis most times I'm sure there's some instructors be like use it for everything in chemistry but I don't know for me um I think I just made case in point for me I find the algebra approach uh to be a little bit SI safer here so you do this if you want um but I don't think I'm going to all right uh yeah so um let me get to the conclusion and I'll do the second bonus example for those who want it I imagine for maybe about half of you after this you'll be ready to turn off the video not offended at all I just provide what people need as much as as little as people people need all right so going back to the um electromagnetic spectrum um hopefully you're able to get a feel for um the scale of things all right so um we were only working in the visible part of the spectrum um today but there is a whole wide electromagnetic spectrum all right we can only see a little sliver of it so I like to ring it from low energies to high energies some books some instructors like to do it the other way um but that's me right radio waves are the lowest uh energy that's used for radios you know communication um microwaves can also be used for uh communication that's uh the way cell phones you know work and WiFi and stuff they work on a microwave level of signal okay so radio waves we're talking about like kilometers you know um really really long and then microwaves we're getting shorter we're getting more on like the meter is scale I mean we could be talking like centim you know millimeters as well but we're we're definitely getting like um shorter uh uh frequencies uh wavelengths for the photons all right INF for red we're getting um even smaller all right and we're around you know a micro uh level um by now okay IR infrared infra meaning before uh red all right we have the visible part of spectrum and the visible part of spectrum is at the nanometer scale all right um little more than nanometers but basically the nanometer scale all right we have UV all right we're getting um even smaller ultraviolet meaning after Violet then we have x-rays or renten Rays um depending on where you're from and then we got gamma rays okay um yeah that's that's how things go all right so um and there's different phenomenon involved but basically uh everything up until here involves um how electrons move uh about uh the nucleus but then when you're talking about gamma rays you're talking about nuclear transitions all right so that's why gamma rays are often associated with uh radioactive materials all right um from a safety point of view we can divide UV um into three categories a b and c all right and the cut off line for safety is a um UVA or maybe about UVA all right uh we can't see UVA but some the animal kingdom can I think like deer and some types of bees or something all right uh UVB and UVC these are um the harmful ones all right so if you were to make a cut off line right there okay everything to the right of the cut off line is what we call ionizing um radiation or ionizing electromagnetic radiation ionizing photons all right uh the ability to uh knock electrons off of atoms and therefore you can create free radicals and do damage so that's what sunscreen is all about protecting um against UV rays all right um now uh x-rays that may bring some fears like oh I have to go get a x-ray um you know at the dentist or something um the amount of x-rays you're exposed to generally speaking are are way way way lower compared to even like standing outside for a few minutes um so um and especially uh technology continues to get improved so you don't need so many doses uh gamma rays they can actually be used in super low um amount ounc for like medical diagnosing purposes um but otherwise this is not something you want Too much exposure to um either all right um but yeah that's your uh a little bit of electromagnetic spectrum and a quick nutshell uh there's pneumonic devices online um or you can make your own for remembering the order um I'll give you mine um it's like real martians oops martians in uh Venus and I guess you should be saying on Venus not in but remember I'm not an English major so real martians and Venus uh use x-ray goggles or something like that all right um if that helps you uh remember the order okay all right last thought before some of you sign off okay I want to give you a sense of familiar numbers when working with photons um maybe you able to follow that calculation with me and um get some numbers uh but uh it's not something we're used to every day so speaking for um myself but I think other instructors as well um it'd be my guess for other instructors and definitely for me that most of my Photon problems revolve around the visible spectrum practically speaking for your average chem 101 student that's what they're going to need in uh their future uh careers and studies okay you know if you're like a chemistry physics you know um other major you might need to work with other wavelengths but um and frequencies but I feel like uh your your uh typical ch11 stud student needs to be most concerned with visible light right so here's my visible light cheat sheet all right visible light cheat sheet so when it comes to energy your uh answers are going to be on the order of 10 to the -19 Jew okay and hopefully you saw that earlier already in our Violet Photon example all right um when it comes to wavelengths the waves uh or excuse me the range of photons that we can see is somewhere around the range of 400 to 800 nanom all right this being your Violet side and this being your red side all right right now you may like whoa you wrote those numbers backwards I thought red was the lower uh energy it is but remember having a longer wavelength means you're a lower energy all right um so you go to the higher numbers you're said to be red shifted you go to lower numbers you're said to be blue shifted um I wish we could say violet shifted but someone else came up with that term and we're stuck with it all right um now if you're working in meters you saw that when we converted these values to meters they were on the order of 10^ the- 7 power all right and then the last thing was a frequency the frequencies for uh visible light and maybe even a little bit of like ultraviolet uh but for visible light is going to be on the order of 10 to positive4 um inverse seconds all right uh for those who are going take care thanks for tuning in for those who wanted to Red Photon calculations uh we can do that too all right so red Photon this time all right so for the red Photon we had um a wavelength of 600 50 nanometers all right and I'm going to ask us the same questions let's get an energy and let's get a uh frequency okay to be a little bit different in this example oh now I'm on the page to be a little different in this example I'll have us go for the frequency first okay so write out your menu of equation you know if that was in your shoes I would just try to do this independently at this point and compare with my answer so yeah I'm inviting you to skip through my video um and then just see the end result so I'm just going to leave the camera on and just uh work this out all right I got a wavelength so I don't want that one this one or that one and I said I was going to get the frequency first so I'm going to do that one first okay oh I forgot to convert that all right frequency done and then let's do an energy okay um I would normally choose this one because Lambda was the original info they gave me but I'm going to show you that uh doing this one would also be okay all right h I'm just using the previous answer on the screen instead of retyping and then multiplying it by the plunks constant [Music] all right there we go so um yeah just to show you that I wasn't making stuff up we can compare the Violet versus red Photon okay and if you want to like write a symbol for Photon you want some shorthand some people will write like H new because that's how you calculate the energy of a photon so the red Photon the red H newu versus The Violet H new um all right so let's see how we did on energy let's see how we did on frequency let's see how we did on wavelength and then you could get like a trick question how about the speed um remember the speed of all photons are the same it's just a speed of light of 3.00 * 10 8 power m/s all right so for the red Photon 3.06 * 10 the -19 Jews okay whereas uh for the Violet photon that was a couple of slides back wasn't it all right 4. 91 time 10 -9 jewles okay all right so Violet one there and then uh let's go on to frequencies we had 4.62 * 10 pi POS 14 inverse seconds and for the Violet Photon 7.41 * 1014 inv second so Violet is the bigger number there okay the wavelength were already given okay and lower energy means longer or bigger uh wavelength if that helps your mind all right so uh there you go all right uh longer video but I wanted to give enough stuff so people could sort uh through and get what they needed um hope this helps uh give any uh comments or suggestions otherwise uh have a good day see you see you um oh there we go