Manual

®
Model No. OS-8515C Teacher’s Guide
65
Experiment 13: Focal Length and Magnification of a Concave Mirror
Part 1: For a distant object, 1/d
o
approaches zero, therefore the image will form clearly with a
mirror-to-screen distance of d
i
= f ≅ 10 cm.
Part 2, typical results:
y-intercept = 1/f = 0.106 cm
-1
x-intercept = 1/f = 0.0979 cm
-1
Answers to questions: 1. The image is inverted. 2. The image is real because it can be viewed on a screen.
3. The magnification is negative because the image is inverted. 4. The three determined values of f are unlikely
to be exactly equal, primarily due to measurement error.
Table 13.1: Image and Object Distances
d
o
d
i
(cm)
1/d
o
(cm
-1
)
1/d
i
(cm
-1
)
Image Size Object Size
50.0 cm 12.5 0.0200 0.0800
45.0 cm 12.9 0.0222 0.0775
40.0 cm 13.4 0.0250 0.0743
35.0 cm 14.0 0.0286 0.0714
30.0 cm 14.85 0.0333 0.0673
25.0 cm 16.3 0.0400 0.0613 2.65 cm 4.05 cm
Table 13.2: Focal Length
f
Result from x-intercept 10.2 cm
Result from y-intercept 9.43 cm
% difference between results from intercepts 8%
Average of results from intercepts 9.82 cm
Result from Part I 10.0 cm
% difference between Average of results from intercepts and result from Part I 1.9%
Table 1.2: Magnification
calculated from image and object distances -0.652
calculated from image and object sizes 0.654
% difference 0.3%
M
M