Switch to the next objective lens and focus again on the metric ...

[mydiamond]

Switch to the next objective lens and focus again on the metric scale on the edge
  of the ruler.
  a. How many millimeters wide is the field of view? Record your measurement
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  in Table 3-2 of the lab manual.

 
  What will be an ideal response?

Question 2

There is a reverse relationship between the size of the field of view and total
  magnification.
  a. Focus on the ruler using the low-power objective lens. How many
  millimeters (mm) wide is the field of view? Record your measurements in
  Table 3-2 of the lab manual. (Hint: Remember that total magnification =
  ocular  objective.)

 
  What will be an ideal response?

[CAPTAINAMERICA]

Answer to Question 1

The diameter of the field of view under the 10X objective is calculated as the
diameter measured for the 10X objective multiplied by 4/10 (the ratio of the
magnification of the two objective lenses.) The diameter of the field of view under
the 10X objective is 4.5  4/10 = 1.8 mm or 1800 m.

Answer to Question 2

Answers will vary. For example, if the field of view is 2 mm and the object occupies
 of the diameter, 2 mm  0.25 = 0.5 mm (or 500 m), the size of the object.
(Review the metric units of length in Exercise 1 if necessary.) Using the 4X
objective, place a transparent 15 cm ruler on the stage and determine the diameter
of the field of view. It is 4.5 mm or 4500 m

[mydiamond]

Great answer, keep it coming

[marict]

Wow, this really help