An insect 1.3mm tall is placed 1.0mm beyond the focal point of the objective len

Question

An insect 1.3mm tall is placed 1.0mm beyond the focal point of the objective lens of a compound microscope. The objective lens has a focal length of 11mm , the eyepiece a focal length of 23mm .

a. Where is the image formed by the objective lens?? answer must be in mm

b. How tall is the image mentioned in part A? answer agian in mm

c. If you want to place the eyepiece so that the image it produces is at infinity, how far should this lens be from the image produced by the objective lens? answer in mm

d. Under the conditions of part C, find the overall magnification of the microscope. how many times

Explanation / Answer

A) Use equation 1/f= 1/s+ 1/s'. The Object is placed 1mm beyond the objective focal point so s=12. 1/11=1/12+1/s'

(1/11)-(1/12)=s'=132mm.

B) Magnification (M)=-s'/s. M=y'/y -132mm/12=y'/1.3mm

y'=14.3mm

C) Use the same equation as in A. 1/f= 1/s+ 1/s'.

We want the image at infinity, so 1/s'=0. Focal point of eyepiece is 23.

1/23=1/s, s=23

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