Investigation A2.2Name______

Title:______Date ______Period_____ Group____

Purpose:

Read the steps of the procedure for parts A & B from the class set and answer the questions for each section.

Parts A & B- Prelab Questions

Label all of the following parts on the microscope to the right:

Eyepiece

Objective

Stage clip

Stage

Fine adjustment

Coarse adjustment

Base

Revolving nosepiece

Low power lens

Medium power lens

High power lens

Power switch

Lamp

Diaphragm

  1. What part would you adjust to allow more light to enter the stage opening?
  2. Which adjustment knob would you use first to locate a specimen?
  3. Which adjustment knob would you use to bring the specimen into clear focus once located?
  4. Which lens do you think would make objects look largest?
  5. What 7 things need to be done before putting the microscope away every time?
  6. Set objective lens to ______power (______lens facing down)
  7. Turn ______& unplug
  8. Make sure it’s ______and ______.
  9. Set objective lens to ______power (______lens facing down)
  10. ______cord ______
  11. Remove any ______- clean and let air dry
  12. Carry with ______
  13. Put in ______

Notice the numbers etched on the objectives and on the lower eyepiece. Each number is followed by an “x” that means “times”. For example, the low-power objective may have the number “10x” on its side as shown in the figure below. The objective magnifies an object 10 times its normal size. The total magnification of a microscope is calculated by multiplying the magnification of the objective by the magnification of the eyepiece. For example:

Magnification

of low-powerX magnification of= Total Magnification

objective eye piece

10X X10X= 100X

  1. Calculate the total magnification for high______, medium______and low ______power.
  1. With which combination of lenses would you be able to see the largest area of specimen?
  1. Which combination of lenses would you use the smallest area with the most detail?
  1. Which number would you set the diaphragm to in order to make your image the brightest?______the dimmest?______

Part C:Using the Microscope – Follow the procedure for part C.

Object Being Viewed / Observations and comments
Letter o
Letter c
Lowercase letter e or r
Mm ruler
(how many mm lines do you see?)

Part C & D. Additional Questions

  1. Which power lens makes the “e” look largest (low or high)?
  1. Which lens has the largest field of view (shows the most area around the “e”)?
  1. When you use a high-powered lens, do you see more of the “e” or less?
  1. How does the letter “e” as seen through the microscope differ from the way an “e” normally appears?
  1. When you move the slide to the left, which way does the “e” appear to move?
  1. When you move the slide up, which way does the “e” appear to move?
  1. The higher power lens has a (larger/smaller) field of view than the lower power lens?
  1. The lower power lens has a (larger/smaller) field of view than the higher power lens?

Part D:

Can you see both hairs sharply at the same focus level? How can you use the fine adjustment knob to determine which hair is crossed over the other?

Sketch the hairs under high power in the circle to the right.

Part E:

Measure the diameter of the field of view. To do this, make sure the low-power objective is in place once again. Put a clearplastic ruler on the microscope stage. Using low power, focus on the millimeter marks of the ruler. Move the ruler so that one of the millimeter marks is at the left edge of the field of view, as shown below. Knowing the diameter of the field of view can help you estimate the actual size of objects seen through the microscope.

  1. Count the number of whole millimeters to the right edge of the field and estimate the fractions to determine the diameter of the field of view. Record the estimated diameter of the low-power field of view in millimetersbelow then repeat with medium and high power.

Objective / Diameter of the Field of View / Area of the Field of View in square mm (mm2)
(see step 13 below)
Millimeters (mm) / Micrometers (µm)
(see step 10 below)
Low Power
Medium Power / 1 mm
High Power / .4 mm
  1. Since microscopic dimensions are very small, they are usually measured in micrometers (µm) rather than millimeters. There are 1,000 micrometers in a millimeter or a micrometer is 1/1000 of a mm. Find the diameter of the objective lens in (µm) by using the following formula.
  2. # of millimeters (mm) X 1000 = ______micrometers (µm)
  1. What is one micrometer (µm) equal to? ______
  1. Now we can estimate the sizes of objects by comparing them with the diameter of the field of vision. For example, a tiny shrimp takes up approximately one-half the field of view under high-power. To find its size in micrometers, use the following formula:
  2. (Proportion of field of view) X (diameter of power objective) = size of object.
  1. Calculate the area of the fields of view using the formula:
  2. A = π r2
  3. A = area and π = 3.14 and r = radius (one half the diameter of the field of view)
  4. Low power ______
  5. Medium Power ______
  6. High Power ______

Discussion Questions 1-3

  1. Summarize the difference between an image viewed through a microscope and the same image viewed with the naked eye.
  1. When viewing an object through the high-power objective, not all of the object(s) might be in focus. Explain.
  1. What is the relationship between magnification and field of view?