Microscope question

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1. Sep 20, 2012

surfahgirl

1. The problem statement, all variables and given/known data

A microscope with a tube length of 160 mm achieves a total magnification of 800X with a 40X objective and a 20X eyepiece. The microscope is focused for viewing with a relaxed eye.

How far is the sample from the objective lens?

2. Relevant equations

M=(Meyepiece)(Mobjective)
Meyepiece=25/Feyepiece
Mobjective = -L/fobjective

3. The attempt at a solution

so I found the fobjective to be 0.4cm and the feyepiece to be 1.25

I'm just not sure what to do next. Which objective do I use to find the distance of the sample? or do you combine them somehow?

2. Sep 20, 2012

PeterO

When the microscope is adjusted for relaxed viewing, it means the light emanating consists of parallel rays. That means the image formed by the objective is at the focus of the eyepiece.
You thus can work out the focal length of the objective [looks like you have, but I haven't checked whether your stated answer is correct] and the distance to the image , so should be able to get the distance to the object.