[Marconis]

So in my bio class we had our first lab as a microscopy lab. Since I am a transfer student, they want me to take freshman bio even though I got a 5 on AP exam which exempt me from freshman bio at my other institution. I state that because I went in all cocky to this lab since I have used microscopes many times before this in my other classes such as Invertebrate Zoology. In that we had a microscopy lab, but we never dealt with a stage micrometer for some odd reason. When this was foreign to me, I felt stressed and embarrassed for myself and the instructor (he was going nuts trying to explain things to people about it) . So, since I am new to it, I want to know if these calculations are correct...

At 4x objective, if 25 stage units fit into 10 ocular units, then is that equal to .25 mm and 250 um? I just did 25x.01mm and then got my answers. I feel like that's wrong.

From an earlier determination that 2.5 stage units fit into 10 ocular units at 40x objective, I calculated that 80 ocular units is the equivalent to 320 um. I did this by doing 80/2.5, multiplying that by .01 and then converting mm to um. Correct?

I hope I'm right, I want to stop feeling like an idiot over such a simple thing

Thanks in advance.

[cypress]

Marconis, on 2 September 2010 - 02:58 PM, said:

So in my bio class we had our first lab as a microscopy lab. Since I am a transfer student, they want me to take freshman bio even though I got a 5 on AP exam which exempt me from freshman bio at my other institution. I state that because I went in all cocky to this lab since I have used microscopes many times before this in my other classes such as Invertebrate Zoology. In that we had a microscopy lab, but we never dealt with a stage micrometer for some odd reason. When this was foreign to me, I felt stressed and embarrassed for myself and the instructor (he was going nuts trying to explain things to people about it) . So, since I am new to it, I want to know if these calculations are correct...

At 4x objective, if 25 stage units fit into 10 ocular units, then is that equal to .25 mm and 250 um? I just did 25x.01mm and then got my answers. I feel like that's wrong.

I believe this is correct. 25 stages/10 ocular units * 0.1 mm/stage = .25 mm or 250 um per ocular unit at 4x.

Quote

From an earlier determination that 2.5 stage units fit into 10 ocular units at 40x objective, I calculated that 80 ocular units is the equivalent to 320 um. I did this by doing 80/2.5, multiplying that by .01 and then converting mm to um. Correct?

25 um / OU at 40x * 80 OU = 2.0 mm You just need to watch the units to help you avoid dividing when you mean to multiply.

Quote

I hope I'm right, I want to stop feeling like an idiot over such a simple thing

Thanks in advance.

It seems like you understand how it works.

[Marconis]

Glad to hear the first is correct. But as for the second, I was wrong? Damn...I remember my lab instructor telling my bench partner that's how to do it. So I have to multiply, not divide?

[cypress]

Yes, but try not to do it from memory, instead reason through the problem based on the information provided.

In the second case you have 2.5 stage units / 10 OU and each stage unit is 0.1 mm so --->

(2.5 SU/10 OU) * 0.1 mm/SU = 0.025 mm/OU You know to multiply because the stage units must cancel this gives you the distance per ocular unit and since you have 80 OU you again multiply so the OU's cancel to get total length of 2.0 mm.

[Marconis]

cypress, on 4 September 2010 - 12:08 AM, said:

Yes, but try not to do it from memory, instead reason through the problem based on the information provided.

In the second case you have 2.5 stage units / 10 OU and each stage unit is 0.1 mm so --->

(2.5 SU/10 OU) * 0.1 mm/SU = 0.025 mm/OU You know to multiply because the stage units must cancel this gives you the distance per ocular unit and since you have 80 OU you again multiply so the OU's cancel to get total length of 2.0 mm.

If the total length is 2.0 mm, that means that the Paramecium is 2000 micrometers. That seems pretty false...what am I not grasping here?

[cypress]

Let's look at it another way to confirm. If the stage glass is in 0.1 mm graduations, and ten ocular units spans 2.5 stages then 10 OU is .25 mm so eight times .25 mm is still 2.0 mm. so 80 OU at 40x is 2 mm unless the stage glass is not 0.1 mm.

[Marconis]

I'm pretty sure each is .01mm or something and the whole stage glass is 1mm (with all the units).

[CharonY]

As long as you do not know the units of graduation the absolute values are guesswork.

[Marconis]

Not quite sure what you're saying.

Through my lab manual it is confirmed that 100 stage units is equal to 1mm.

[cypress]

From your first answer I took the stage divisions to be 0.1 mm, my mistake. But if they are instead 0.01 mm then both answers get divided by ten, and you get 25 um at 4x power for one OU and 0.2 mm for 80 OU at 40x.

[Marconis]

Ah, you're totally right man. I found a formula:

one space on the OM= X spaces on SM x .01mm/ 10

Thanks so much for your help.

So are these all right? I found an easy formula for the last part too

Number of SM units in 10 OU @4X: 25 One OM unit= .025mm,25um
Number of SM units in 10 OU @10X:10 One OM unit=.01mm, 10um
Number of SM units in 10 OU @40X: 2.5 One OM unit=.0025mm, 2.5um

By doing (length of one division of the ocular micrometer)(number divisions counted as length Paramecium caudatum).
So (80)(2.5)

80 OU divisions @ 40X= 200um
70 OU divisions @ 40X= 175um

This post has been edited by Marconis: 4 September 2010 - 11:43 PM

[cypress]

Yes, it is all correct. You've got it.

[Marconis]

Thanks for your help, cypress.