PASCO OS-8500 INTRODUCTORY OPTICS SYSTEM - Manual (Page 55)

012-02744K Introductory Optics System
®
49
EQUIPMENT NEEDED:
-Optics Bench, Light Source -75 mm Focal Length Convex Lens
-150 mm Focal Length Convex Lens -Variable Aperture
-Component Holders (2) -Viewing Screen
Experiment 22: The Compound Microscope
Figure 22.1 The Compound Microscope
Introduction
A compound microscope uses two lenses to provide greater magnification of near objects than is
possible using a single lens as a magnifier. The setup is shown in Figure 22.1. The objective lens,
L
1
, functions as a projector. The object is placed just beyond the focal point of L
1
so a real, magni-
fied, inverted image is formed. The eyepiece, L
2
, functions as a magnifier. It forms an enlarged
virtual image of the real image projected by L
1
.
The real image that is projected by L
1
is magnified by an amount m = -d
i
/d
o
, as indicated by the
Fundamental Lens Equation. That image is in turn magnified by the eyepiece by a factor of 25 cm/f
(see Experiment 20: The Magnifier). The combined magnification is, therefore:
M = (-d
i
/d
o
) (25 cm/f).
Procedure
Set up the microscope as shown in Figure 22.1. Use the 75 mm focal length lens as the objective
lens and the 150 mm focal length lens as the eyepiece. Begin with the objective lens approximately
150 mm away from the object (the Viewing Screen). Adjust the position of the eyepiece until you
see a clearly focused image of the Viewing Screen scale.
➀ Is the image magnified? How does the magnification compare to using the 75 mm focal length lens
alone, as a simple magnifier?
__________________________________________________________________________
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While looking through the eyepiece, slowly move the objective lens closer to the Viewing Screen.
Adjust the position of the eyepiece as needed to retain the best possible focus.
f
1
L
1
f
2
L
2
d
o
d
i
L
2
(Eyepiece)
f
1
f
2
Object
d
o
150 mm
L
1
(Objective
Lens)