Grade 10 Academic Science – Biology
Compound Light Microscope
Label the parts of the Compound Light Microscope
1
7
2
8
3
9
4
10
5
11
6
12
Compound Light Microscope
Parts
1
Body Tube
7
Light Source
2
Ocular Tube
8
Base
3
Revolving Nosepiece
9
Ocular Lens (Eyepiece)
4
Objective Lens
10
Arm
5
Stage
11
Coarse Adjustment Knob
6
Diaphragm
12
Fine Adjustment Knob
Different Types of Microscopes
Simple Light Microscope

Has a single lens

Uses a simple light source (e.g., candle or sun)

Used by scientists in the 17th Century
Compound Light Microscope

Uses two lenses (ocular and objective)

Uses visible light from electric lamp(s)

Provides magnification up to 2000X

Used in schools for teaching
Calculating Magnification
Ocular lens X Objective lens = Total Magnification
e.g., (10X) X (40X) = 400X Magnification
Transmission Electron Microscope (TEM)

Uses an invisible beam of electrons

Requires specimen to be very thin for the electron to pass through

Can only be used to view DEAD cells

Built in Toronto in 1937 with Magnification of 7000X

Can provide 5,000,000X Magnification with modern TEM
Scanning Electron Microscope (SEM)

Uses magnets to reflect electrons from the surface to the specimen

Allows for thicker specimens to be viewed

Can be used to view surface features of things such as insects

Cannot magnify as great as TEM (best is 300,000X)

Provides greater contrast and depth
Grade 10 Academic Science – Biology
Math and the Microscope
We have started using the compound microscope. To effectively explore the image viewed, we
must also understand the magnification of the image. The following information should explain
how magnification is determined.
Calculating the TOTAL MAGNIFICATION of a Compound Light Microscope
Total Magnification = Ocular Lens X Objective Lens
Using your microscope…
1.
What is the magnification on LOW power (i.e., lowest Objective Lens setting)
2.
What is the magnification on MEDIUM power?
3.
What is the magnification on HIGH power?
Finding the FIELD OF VIEW (FOV) on LOW power
·
Turn to the Low Power objective lens
·
Place a clear plastic ruler with mm markings on top of the stage
·
Focus your image
·
Move the ruler so that one of the mm markings is at the edge
·
Count how many divisions of the ruler fit across the diameter of the Field
of View
·
Multiply the number of divisions by 1000 to obtain FOV in micrometres
(m)
·
Record this value in m (Recall: 1 mm = 1000 m)
What is the FOV on LOW power? ________________ m
Use this equation to find the FOV on MEDIUM power.
FOV = Total Magnification Low Power X FOV Low Power / Total Magnification Medium Power
What is the FOV on MEDIUM power? ________________ m
Use this equation to find the FOV on HIGH power.
FOV = Total Magnification Low Power X FOV Low Power / Total Magnification High Power
What is the FOV on HIGH power? ________________ m
Estimating the SIZE of an object
- Estimate how many times the object will fit across the Field of View
- Calculate the size of the object using the formula below
- Remember size is in m
Estimated Cell Size = FOV on given power / Number of cells that fit across FOV
Optional Activity
- Choose a prepared slide
- Focus the cells on Medium or High Power
- Draw a sample of the cells
- Calculate the size on one cell (showing work)
PRACTICE
1.
Ocular Lens is 25X and Objective Lens is 40X. What is the Total Magnification?
2.
You want a Total Magnification of 1000X. You have an Objective Lens of 100X. What
size of Ocular Lens do you need?
3.
You want a Total Magnification of 500X. You have an Ocular Lens of 15X. What size of
Objective Lens do you need?
4.
Objective Lens is 25X and Ocular Lens is 15X. What is the Total Magnification?
5.
You need to determine FOV on the Low Power setting. You measure 5.5 mm across the
view. What is the FOV for Low Power in :m?
6.
Total Magnification for Low Power is 100X, while Total Magnification for Medium Power is
500X. Using your answer in #5, what is the FOV for Medium Power?
7.
You determine 25 cells were visible on Medium Power. Using your answer from #6, what
is the size of one cell?