identify the parts of a compound light microscope and explain their functions define magnification ...

Identify the parts of a compound light microscope and explain their functions

Define magnification Calculate the total magnification of the

lenses that you are using to view an object Describe the microscopes resolution, depth

of field, and field of view Describe how to prepare a slide How to use a microscope properly Describe how to correctly put a microscope

away after use

Tool used by biologists to see objects that are very small

Light passes through the specimen & through two sets of lenses (compound)

Specimen must be small enough & thin enough for light to pass through it, if not only a black silhouette can be seen

Eyepiece (Ocular)◦ used to view specimen

(what you look into)◦ holds a lens

Body Tube◦ permits light to pass

through◦ separates the

eyepiece from the nosepiece

Revolving Nosepiece◦ holds objectives ◦ used to turn

objectives into position

High-power objective◦ holds a lens◦ used to make

specimen larger for more detail

◦ magnifies 40x

Low-power objective ◦ holds a lens◦ used when first

focusing in on a specimen

◦ magnifies 4x

Stage ◦ used to hold

specimen

Stage clips ◦ used to hold slide in

place

Diaphragm ◦ regulates the

amount of light that passes through the stage

Mirror/Light source ◦ used to reflect/emit

light

Coarse adjustment ◦ used to raise and

lower body quickly for focus

use first on low & medium power for approximate focus (but never use with high power objective)

Fine adjustment ◦ used to make image

clearer use for final

focusing on low & medium power (ALL focusing on high power!)

Arm ◦ used to carry

microscope

Base ◦ used to support

microscope◦ also used to carry

the microscope

Purpose of microscope is to magnify an image BUT all microscopes are not created equal

Two scopes can have identical magnifications, but have differences in the qualities of resolution

Which microscope is more expensive?

Magnification-the enlargement of an image created by the lenses

Our compound light microscopes have lenses in two locations◦ 1. ocular/eyepiece◦ 2. objectives

low power 4x medium power 10x high power 40x

Objective lens magnification X Eyepiece magnification = Total Magnification ◦ i.e. 40X x 10X = 400X

Resolution- (sharpness of an image) the capacity to show fine detail in clear focus

Using a cheaper scope with inferior resolution, it may be difficult to distinguish two things that are very close together; they may blur together to appear as one

The term depth of field refers to the thickness (depth) of the layer that is currently in focus◦ When one layer moves out of focus, another layer

above or below the first layer, moves into focus

The illuminated area that you are viewing is called the field of view◦ Higher power objective lenses have a smaller field

of view

Obtain a clean slide & coverslip Place specimen in middle of slide Place a drop of water on specimen Hold coverslip by thin edges between index

finger and thumb 45 degree angle into drop of water After water spreads along one edge of

coverslip slowly lower until it lies flat on top of the slide

IF bubbles try again Remove excess water with paper towel Add drop to edge if it dries out

Start on low power, medium light setting Use coarse adjustment to first attempt to find

the specimen Once you have located the specimen using the

coarse adjustment, finish focusing with the fine adjustment

Adjust light if necessary To switch to medium, simply rotate nosepiece,

refocus with fine adjustment, adjust diaphragm and position of slide as needed

To switch to high, repeat the steps above BUT BE CAREFUL THAT THE OBJECTIVE DOES NOT HIT THE SLIDE!!

Rotate the nosepiece to the low power objective

Lower the body tube of the microscope down as close to the stage as possible by using the coarse adjustment

Wrap the cord neatly around the base Place the plastic cover back on the microscope

& return it to its proper slot within the cabinet

**Make sure that lab stations are neat & clean so your group does not lose any lab points!!**

Pick a small area to “blow up” in your sketch Fill the entire circle (PENCIL ONLY) Label your sketches Calculate total magnification for each sketch Give a brief description of each specimen’s

appearance ALL sketches should be done on either

medium or high power unless specified to sketch at low power

**You must have your slide checked by me & your lab sheet marked before returning your clean slide to your lab station!** (If you do not do this your group will lose lab points)

**Make sure that lab stations are neat & clean so your group does not lose any lab points!!** (If lab stations are left messy all groups assigned to that station will lose lab points)

Prepared Slide (from front of room) Feather (small piece obtain from Mrs.

Pettigrew) Butterfly wing (small piece of wing)

NO WET MOUNT Human hair or cat hair (small sample) Complete lab sketches & questions in handout

(letter “e”, magazine picture, & yarn exercise)