Question

1.) Estimate the length of each of the following objects in um:

(400x) (100x)

2.) How does a microscope's iris diaphragm lever work like the iris of an eye?

3.) Assume that you are using the low-power objective and an object takes up a quarter of the field of view. Estimate the diameter of the object in um.

4.) Indicate a possible solution for each of the following complaints during microscope usage:

a.) There is not enough light to view a specimen:

b.) I can't find the specimen on the slide:

c.) I see a dark crescent-shaped structure.

Answer 1

This question deals with compound microscope.

1) The scale of length measurement of the field of view is in mm. The field of view for a 40X objective would be around 4.5mm. Thus, length of object for 400X would be 40/400 x 4500 = 450um. For 100X objective it would be 40/100 x 4500 = 1800 um.

2) The iris is a circular structure in the eye which controls the diameter and aperture of the pupil which ultimately controls the intensity of light reaching the retina. In a similar way compound microscopes are fitted with a rotating disk called as diaphragm of iris which has different sized holes of different diameters. They are adjustable and have a function similar to that of the iris in eye. They control the intensity of light and help in maintaining contrast and resolution.

3) If an object takes quarter of the field of view, its size would be 0.25 times the size of field of view which ranges from 16-18 mm for a 10X objective (low power). Thus the diameter of the object would be 0.25 x 16 = 4mm. This calculation is based on estimations. Values will vary with different parameters and objectives.

4) a) If there is not enough light, then the iris diaphragm can be used to enhance the contrast. Also the condensor can be tweaked a bit.

b) To find the specimen use a low power objective to identify the location of the specimen on the field of view. After focusing on the required area switch to the appropriate objective.

c) Adjusting the light mirror and tweaking the condensor will solve the problem.

"A malaria biologist"