A student finds a 12-cm long metal tube with a lens attached to one end.The attached lens has a focal length of 0.60 cm.The student wants to use the tube and lens to make a microscope with a magnification of 100x.What focal length lens should the student attach to the other end of the tube?
A)0.12 cm
B)0.86 cm
C)5.0 cm
D)14 cm
E)60 cm

Question

Quizplus · Accepted Answer

We can use the magnification formula for a microscope:

M = (-)fo/fe

where M = magnification, fo = focal length of the objective lens, and fe = focal length of the eyepiece lens.

We are given M = 100x, fo = 0.60 cm, and the length of the tube (which we can assume is the distance between the objective and eyepiece lenses) is 12 cm.

First, we need to find fe:

100 = (-)0.60/fe

fe = (-)0.006 cm

The negative sign indicates that the image will be inverted.

Since the absolute value of fe is very small, we know that the eyepiece lens should have a larger focal length than the objective lens to achieve a reasonable length for the microscope.

Therefore, the best choice is C, 5.0 cm.

A Student Finds a 12-Cm Long Metal Tube with a Lens