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today's video is going to concentrate on microscopes so far we from talking a little bit about cells and we realized that cells are quite small most cells you can't see with the naked eye so in order to see ourselves we need to use a microscope commonly the microscope we're going to be using in class is called a compound microscope it magnifies the specimen that you're trying to look at when you place it on the slide magnifies with one of the objective lenses and also magnifies with what we call the ocular or IPS typically our eyepieces magnify 10 times and most of our microscopes have three objective lenses with varied magnifications on them you would rotate the objective lenses around in order to change the magnification in order to figure out how much the microscope is magnifying your image in total with the objective lenses and the eyepiece you would need to calculate it so in order to calculate total magnification how much your image or your specimen is being magnified or increased you would multiply the eyepiece magnification by the objective lens magnification in order to figure out how much it's magnifying totally so our example if the eyepiece magnification is 10 X or 10 times and our objective magnification is 60 X or 60 times we would calculate total magnification by multiplying the eyepiece magnification of 10 by the objective magnification of 60 to get an answer of 600 X why don't you pause the video for a second and try the second sample that's in your note packet so the second sample that you tried in your note packet you are attempting to calculate the total magnification of a microscope that has an objective of 43 times or 43 X and an eyepiece of 10x when you multiply them together you should have gotten 430ex unfortunately sometimes when we look at things underneath a microscope they're so tiny it's so hard to tell how big they really are so one of the things that we do is we can measure underneath the microscope typically when we look through the microscope the area that you can see we call the field of view which is often abbreviated FOV now our typical microscope and a magnification total magnification of 430 X might have a diameter or total diameter field of view of two point four millimeters now if you were to think about how big that really is if this were my microscope and I needed to measure two point four millimeters it's pretty tiny those are the smallest lines on my ruler right here is very small so one of the things we might do as we're measuring under the microscope is use an even smaller unit than millimeters we would convert it to something called micrometers so our conversion from millimeters to micrometers for one millimeter there are 1000 micrometer x' now if you can imagine this ruler again this ruler the small lines in between the very small lines is one millimeter in between those lines would be 1,000 marks to indicate micrometers so it's pretty tiny unit that we're measuring in an example of converting from millimeters to micrometers if I had a measurement of two point four millimeters I would multiply by 1000 because we have 1000 micrometer x' for every millimeter and i would end up with an answer two thousand four hundred micrometers when you're converting from millimeters to micrometers you can also move the decimal point from its original place to the right three places if you are converting from millimeters to micrometers if you are going from micrometer to millimeters instead of multiplying by a thousand you would divide by a thousand instead of moving our decimal point to the right three places you could move your decimal point to the left three places for converting why don't you try the practice problem in your packet hit pause when you're done with the practice problem press play again we'll see how you did so let's see how we did with our practice problem converting if I were to measure my field of view of one point two millimeters as you can see here my one point two millimeters if I wanted to convert it to micrometers I would multiply by 1000 so 1.2 times 1000 would give me an answer of one thousand twelve hundred micrometers now if I were trying to measure underneath the microscope it would be really handy to have a ruler that I could use under the microscope in order to be able to do that measuring but often times things are so small that you wouldn't even be able to get that measurement accurately if you look at my example right here if I were under my lower objective lens this would be my first millimeter mark if I were to take a clear plastic ruler and put it underneath the stage I could see one millimeter mark here and then another millimeter mark right there my diameter would be about one point two millimeters if you were trying to measure something that didn't fit that whole field of view you would not be very accurate at it so one of the things that we tried do as we try to do an estimation in order to determine the size of an object when reviewing it underneath the microscope we know what our typical diameter is for our field of view if we had an object that looked like this as we were looking at it under our lower objective lens what we try to do is we try to estimate two ways you can estimate by saying I think that that object takes up about 1/4 or 25% of the diameter of the field of view or I could say that if I lined up these objects side by side right next to each other across the diameter I could probably fit four of them across my diameter so in order to estimate the size of the object you would take your measurement for the size or the diameter of the field of view in micrometers and you would divide by the number of objects that you thought that you could fit across or the fraction that you felt it took up so in this particular example with a diameter of 1200 micrometers if I thought that I could line up those objects four of them in a row across the diameter and we divide one thousand two hundred micrometers by four to come up with an answer of three hundred micrometers and that would give me the diameter or size of that one individual object as opposed to all four of them for the diameter of the field of view what I'd like you to do is I'd like you to hit pause on your video again and I'd like you to try the example that's in your packet press play when you're done and we'll see how you did so in the example in your packet we had six objects that would fit across our field of view the last example remember we had four this time we had six and we're going to stick with the same field of view of one thousand two hundred micrometers because we're going to use the same microscopes that we usually use so again in order to figure out the size of the object we're going to take our diameter of our field of view in micrometers and divide it by the number of objects we think we can fit across the diameter in order to come up with our answer for the diameter of one object so twelve hundred micrometers divided by six gives us an answer of two hundred micrometers that's it for measuring with a microscope today and magnification of a microscope try to finish the rest of the sample problems in your packet tonight for homework and we'll answer up some questions tomorrow thank you