To examine a particular blood sample in biology lab, a student uses a compound m

Question

To examine a particular blood sample in biology lab, a student uses a compound microscope set to have a magnification of -4520. The objective and eyepiece are both attached to a tube which is 17 cm in length and the eyepiece has a focal length of 2.51 cm. The near point of the person using the microscope is 25 and you can assume she can view the image produced with a fully relaxed eye.

1.) What is the focal length of the objective?

f =

2.) What is the distance between the blood sample and the objective lens?

do =

Explanation / Answer

For eye piece, assume v = 25 and f = -2.51 and calculate u1 for eye piece as

u1 = (25*2.51)/[25+2.51] =2.28 cm

This gives image distance from the objective as 17 - 2.28 = 14.72 cm

(14.72/d)*(25/2.28) = 4520 giving d = 0.0357 cm

Applying lens formula, we get focal length of objective as (14.72*0.0357)/[14.72+0.0357] = 0.0356 cm

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