Situation
The objective and the eyepiece of a microscope have focal lengths of 4.0 mm and 25 mm, respectively. The objective produces a real image 30 times the size of the object. The final image is viewed at infinity. The near point of the microscope user is at 25 cm.
-In Situation above, the distance between the object and the focal point of the objective, in mm, is closest to:
A) 0.13
B) 0.18
C) 0.23
D) 0.28
E) 0.33

Question

Quizplus · Accepted Answer

The magnification of the objective is given by the formula M = (L - f_o) / f_o, where L is the distance from the objective lens to the real image. Given M = 30 and f_o = 4 mm, solving for L gives L = 124 mm. The object distance (u) is then found using the lens formula 1/f_o = 1/u + 1/v, where v = L. Solving for u gives approximately 0.13 mm.

Situation The Objective and the Eyepiece of a Microscope Have Focal