PASCO OS-8515C Basic Optics System - Manual (Page 37)

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M o d e l N o . O S - 8 5 1 5 C Experiment 13: Focal Length and Magnification of a Concave Mirror
37
Experiment 13: Focal Length and
Magnification of a Concave Mirror
Purpose
The purpose of this experiment is to determine the focal length of a concave mirror
and to measure the magnification for a certain combination of object and image dis-
tances.
Theory
For a spherically curved mirror:
(eq. 13.1)
where f is focal length, d
o
is the distance between the object and the mirror, and d
i
is
the distance between the image and the mirror. 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 mirror by making a single mea-
surement of d
i
with .
Procedure
1. Hold the mirror in one hand and the half-screen in the other hand. Use the con-
cave side of the mirror to focus the image of a distant bright object (such as a
window or lamp across the room) on the half-screen. (See Figure 13.1.)
2. Have your partner measure the distance from the mirror 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
Concave/convex Mirror
Half-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
∞ ≅
Distant
Object
Half-screen
Mirror
Image
Figure 13.1