How does a microscope\'s iris diaphragm lever work like the iris of an eye? ____

Question

How does a microscope's iris diaphragm lever work like the iris of an eye? ____ For each of the following parameters, indicate whether it increases or decreases as you move from lower magnification to higher magnification. a. Field diameter ______ b. Working distance ______ c. Amount of light required ______ d. Resolution ______ 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 mu m. ______ A student is using the high-power objective. His lab partner notices that the working distance is approximately 1 cm. Is the student observing the specimen? ______ Explain. ______ 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: ______

Explanation / Answer

1) The written answer is correct.

2) For low power to high power objective magnification change, field of view decreases, amount of light required increases, working distance decreases, resolution decreases.

3) As we are using a low power objective, magnifying power of the objective is 4 (written 4X). If the magnifying power of the ocular lens is 10 (written 10X), then magnifying power of that lens combination is 40X.

Using ocular lens = 10X and the low power objective = 4X, and if the field of view =2.5 mm, then the diameter of the fielf of view under high power objective (40X) ,will be

diameter of field of view X magnification of low power objective   = 2.5 X (4x) / 40)x = 0.25 mm

   magnification of high power objective

0.25 mm = 250 micrometre.

As the object takes quarter of the field of view, diameter of the object = 1/4 X 250 micrometre = 62.5 micrometre.

Note : Over here diameter of field of view has not been mentioned, so we are arbitrarily considering it to be = 2.5 mm.

4) Working distance is the distance between front part of lens of the objective and the cover slip. It is inversely proportional to magnification of objective lens. that is, it is less for high power objective and vice versa. Working distance of 1 cm = 10 mm is very high for a high power objective lens. It is generally in the range of decimals of a millimetre. So, we cannot say that the student is observing the specimen.

5) a. The condenser is to be adjusted to receive maximum light supply while observing a specimen under a given objective lens.

b. Focus knob is to be used to place the sample into focus and the condenser is to be readjusted to have the sufficient amount of light to view the specimen.

c. If there is a dark crescent shaped structure, it means the lens of the objective has touched the cover slip of the slide. the lens is to be lifted up by focus knob and if required magnification of objective is to be decreased to get a larger working distance and specimen is to be focussed again properly using focus knob. If required condenser is to be adjusted for proper light supply under new magnification objective.

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