Hello students, Ms. Watson here and today we're going to learn how to do some calculations about our microscope images. So what are our learning goals today? Well there are three learning goals, one for each of the different types of calculations we're going to learn today. So the first is that you should be able to calculate the total magnification of an image. The second that you should be able to calculate the field of view of the high power lens.
And the third you should be able to measure the specimen size. So those are our three learning goals for today. So let's start off with the magnification. Total magnification.
is the magnification of the ocular lens times the magnification of the objective lens. So let's take a couple examples here. If the ocular lens is 10 times magnified and the objective is 4 times magnified, 10 times 4 gives us 40. So the total is 40 times magnified. Let's look at another example here.
If the ocular lens is 10 times magnified, And the objective lens is also 10 times magnified. 10 times 10 gives us 100, so the total power is 100 times magnified. Let's look at our next calculation. So we need to understand what a field of view is before we can calculate our fields of view.
So the field of view is the diameter of the circle of light that we can see through a microscope. So when we look at a microscope, we see a little circle and the image is inside of it. Well, the diameter of that circle is our field of view.
So for low power and often for medium power, particularly with the microscopes that we use in our school, for low power and medium power, you could actually use a ruler to calculate the field of view. So you just put the ruler underneath the microscope, and that will give you the field of view. So let's take a look at how you would do that. Normally, when we use a ruler, the very first notch there is zero, zero.
and then we calculate for we count from there 1, 2, 3 and so on we would do the exact same thing when calculating the field of view so we put the very first notch at the very edge of our field of view so you can see right here this one is at the very edge of the field of view and then we count across to see the total field of view so here we would count 1 2, 3, 4 so our field of view would be 4 mm because this ruler has little dashes in millimeters. So the total field of view is 4 mm and we just count across that way. And this is pretty typical for our low power lenses on the microscopes that we use in this school. So for high power, if we put a ruler underneath the microscope at high power, we're going to find that typically it's less than 1 mm.
So we can't really use the ruler to determine what the field of view is. Because it's less than 1 mm, it's smaller than our smallest ability to measure, so we need to do some calculations. So first we would find the low power field of view. We would need to find the magnification of the low power and the magnification of the high power.
and then we would use this equation to determine the view for the high power. So let's take a look at how we might do that. If the low power is 40 times magnified, and it has a diameter of 2 millimeters, and we want to know the diameter for the high power, which is 400 times magnified.
So how would we do that? Well, let's see. We're going to start off by writing the equation, and I'm just going to shorten it a little bit. So HP, and I'm going to put a little subscript D instead of writing the full word diameter there, over the low power diameter. And that's equal to low power, and I'm going to put a little M for magnification, over high power magnification.
And let's rearrange that equation. We're trying to determine the diameter for the high power. So that would be here HP.
diameter and that's equal to low power magnification over high power magnification. And in order to get rid of this low power diameter down here, remember you do opposite operations since it's division right here, we would multiply on the other side. So here times low power diameter. So let's plug our numbers in. So the high power diameter is going to be equal to the low power magnification, which is 40 times magnified, times the low power diameter, which we said was 2 mm, over the high power magnification, which we said was 400 times magnified.
So that means our high power diameter... If we do our math, it's going to be 0.2 millimeters across. So 0.2 millimeters, we can see that's much smaller than 1 millimeter, so putting a ruler under the microscope wouldn't have helped us figure out this calculation.
So finally, specimen size. Specimen size is the field of view, that's FOV is field of view, divided by the number of specimens across the diameter. So if we take a look at this picture, if we say the field of view is about 4 millimeters, what would be the specimen size of that green one? Well, I'd say maybe two of them could fit across the diameter of the field of view.
So we would say 4 millimeters. divided by 2, and that would give us 2 millimeters. So the specimen size is 2 millimeters. Let's take a look at the yellow one. Now we could look at the height or the width.
Let's look at the width for this example. So I'd say you could fit approximately 10 of those little yellow ones across the fields of view this way. So if we say 4 millimeters divided by 10 specimens, That's going to give us 0.4 mm. So they're 0.4 mm across. Let's take a look at the red one.
I'd say probably three of those would fit across the field of view. So if we do 4 mm divided by 3 of those, and that gives us about 1.3 mm for the specimen size. And then the last one, the brown one, I'd say probably 3 would fit across for that one too. So it would be the same calculation.
4 mm fields of view divided by 3 specimens gives us 1.3 mm per specimen. So that's how we would calculate the specimen size. So let's take another look at our learning goals.
You should be able to calculate the total magnification. You should be able to calculate the field of view of the high power. And you should be able to measure the specimen size when you're given the field of view and the number of specimens across the diameter. So if you can do all these things, fantastic. If not, please re-watch the video.
And if you're still having any questions, come ask me in class tomorrow. All right, that's all for now. Bye-bye.