light microscopy obviously like microscope the i mean it's in the name basically it uses light okay it uses light to visualize a specimen now students hate this part a lot of students especially hate this but they're like you'll be like oh my god i'm studying biology why do i have to look at physics what does physics have to do with this because we're gonna have to look at wavelength of light just a little bit so if you're not a physics student you know uh you might have to just uh spend about a good five minutes for this now light is an electromagnetic wave you don't have to memorize that for the exam but what you'll have to know is different types of light have different frequencies light itself basically i'm not the best at following this i'll find my best you have like different frequencies of light so and i always love to ask my students which one is considered high frequency and which one's considered low frequency uh if you are not so sure or if you know it let's just take some time let's just consider the question now low frequency of light is this one where the peaks and the valleys do not occur very frequently basically so it takes some time for it to occur like this much of length there is only one peak and there's only one valley we call that low frequency but high frequency is the peaks and the valley appear much quicker we can just look at it that way you don't have to memorize what's the definition of low frequency and high frequency but what you'll have to know is you'll have to kind of identify it if you are looking at a diagram which is considered low frequency and which is considered high frequency now high frequency light i guess that's purple yeah violet okay two certain extent my colors i'm not so good with my colors this is high frequency it is extremely important to know that red light red light is considered a low frequency light green falls somewhere in the middle over here and violet is considered high frequency it should be just basically next to violet you must also know the wavelength now when we're talking about the wavelength of light the wavelength of light is just basically the distance between this peak to this peak of this valley to this valley that's the wavelength of light it is usually symbolized as lambda now so if they ask you the frequency of red light and the frequency of violet light what do you think look at look at the distance between these two peaks over here and look at the distance between these two peaks over here i'm just going to highlight it so that you can see it a bit more clearly i'm just going to highlight these areas so who will have a higher wavelength what do you think if you say that that light will have a higher wavelength you are correct red light has a wavelength of about 700 nanometers and remember in the previous video we did in introduce the concept of nanometers okay so that's a new one by the way and violet light will have a frequency of about give or take 400 nanometers now why does this matter a lot of students are like why do i care about this why do i have to give a damn about you know the length of what the wavelength of life how does this matter in biology kind of does so in cambridge it is extremely important to know for your a levels that red light has a frequency of 700 a wavelength of 700 nanometers it's a low frequency wavelength and violet light has a 400 nanometer wavelength and its high frequency all right now why is this a big deal or why do i care i love to ask my students these questions why do i have to care about this okay how does this apply into microscopy or to visualize a specimen now if you remember just a bit of revision from the earlier video i mean the previous video the previous video i stated that if you want to visualize an object okay or a specimen the light must first be able to hit the specimen and reflect the specimen into i mean reflect the light into our eyes only then we will be able to see it this is what i mentioned in the uh earlier video now so let's apply this you see there are certain structures in a cell that are too small to be seen using light what do i mean by that let's consider the chloroplast now the chloroplast itself is a very large organelle the size may vary but let's just say that the size of the organelle is 2 000 nanometers all right and let's also put another organelle over here and that organelle i'm just gonna overhead the bottom is a ribosome okay and the ribosome over here is actually only it should be smaller than that by the way so i hope maybe i should make it into like a are you able to see this like like a green dot over there i hope you're able to see that green dot and the ribosome is about give or take 23 nanometers let's just put 23 nanometers now imagine if i were to shoot light i don't care what color light i shoot on it let's just say i just gave it red light now red light has a frequency of 700 nanometers so basically what will happen is it will just basically move along okay and as the red light moves along does it hit the chloroplast it hits the chloroplast and because it hits the chloroplast the chloroplast interrupts light and reflects it so in this case if it's reflected will we be able to see it the answer is yes you can use a light microscope and you can actually visualize the chloroplast in a cell so in in other words you can actually view a chloroplast using a light microscope now let's shift the focus to the ribosome which is about 23 nanometers i'm going to ask you a question right now will we be able to see the ribosome using red light or violet light for that matter will we be able to see it the answer is probably no because what actually happens what do you notice what is happening over here exactly the red light just passes through the ribosome the ribosome does not have the capability of interrupting the light so how now can so can we see ribosomes using a light microscope no we can't we will not be able to visualize a ribosome because they are too small