®
M o d e l N o . O S - 8 5 1 5 B
E x p e r i m e n t 1 2 : F o c a l L e n g t h a n d M a g n i f i c a ti o n o f a T h i n L e n s
31
Experiment 12: Focal Length and
Magnification of a Thin Lens
Purpose
The purpose of this experiment is to determine the focal length of a thin lens, and to
measure the magnification for a certain combination of object and image distances.
Theory
For a thin lens:
(eq. 12.1)
where
f
is focal length,
d
o
is the distance between the object and the lens, and
d
i
is the
distance between the image and the lens. By measuring
d
o
and
d
i
the focal length can
be determined.
Magnification,
M
, is the ratio of image size to object size. If the image is inverted,
M
is negative.
Part I: Object at Infinity
In this part, you will determine the focal length of the lens by making a single mea-
surement of
d
i
with
.
Procedure
1.
Hold the lens in one hand and the screen in the other hand. Focus the image of a
distant
bright object (such as a window or lamp across the room) on the screen.
2.
Have your partner measure the distance from the lens to the screen. This is the
image distance,
d
i
.
d
i
= _______________
Analysis
1.
As
d
o
approaches infinity, what does 1/
d
o
approach?
Required Equipment from Basic Optics System
Light Source
Bench
Converging lens of unknown focal length
1
1
Instructors: see note on page 51.
Screen
Other Equipment
Metric ruler
Optics Caliper (optional, for measuring image sizes), PASCO part OS-8468
1
f
---
1
d
o
-----
1
d
i
----
+
=
d
o
∞
≅
Summary of Contents for OS-8515B
Page 6: ... Basic Optics System About the Experiments 6 ...
Page 26: ... Basic Optics System Experiment 9 Apparent Depth 26 ...
Page 38: ... Basic Optics System Experiment 13 Telescope 38 ...
Page 42: ... Basic Optics System Experiment 14 Microscope 42 ...
Page 44: ... Basic Optics System Experiment 15 Shadows 44 ...
Page 46: ... Basic Optics System Telescope and Microscope Test Pattern 46 ...