PHYSICS 125 LAB 8: SPHERICAL LENSES
Goal:
This lab will investigate image formation from spherical lenses.
Background reading:
Review section 23.3. You may want to draw the ray diagrams requested in this Lab Report
before coming to class.
Equipment needed:
Optics Kit with cylindrical concave and convex lenses
Light box configured to produce 3 or 4 rays of light
PASCO linear optical bench with “object” source (light box and wall plug)
White viewing screen, mounted half-screen, mounted lenses with f = + 100 mm and - 150 mm
White index cards (3”x5” and/or 4”x6”), paper, protractor, 4 rulers, flashlight, and table lamp
Experimental Procedure:
Lenses – ray tracing using light box and cylindrical lenses
Use three or four rays and observe the paths of the rays through the converging lens. Trace the
rays with pencil, and be sure to mark the position of the lens, to determine the focal length of the
lens. Repeat with the diverging lens. Now try putting the two lenses in contact and observe the
rays. Turn in your sheets with the drawings, along with the rest of the lab report.
Converging
Diverging
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Convex Spherical Lenses
Show that the image of an “object at infinity” is located at the focal length from the convex lens.
Go over to the window with a spherical convex lens (mounted on the black plastic mount) and
obtain a real, inverted image of the dormitory. With the help of a lab partner, determine the focal
length of the lens, using a ruler to measure the distance from the lens to the index card on which
you see the real image. Let each lab partner determine the focal length, record each value, and
average these to get an average result. Compare with the value printed on the plastic mount.
Convex Spherical Lenses: various cases
Mount a lens with f = + 100 mm on the optical bench and determine values for the four cases
listed in Data Table 2. These should be easy to see using the screen on the bench. One of the
cases will have a virtual image!
Concave Spherical Lenses
Mount a concave lens on the bench and look through the lens to see the virtual image.
Record your observations in the Lab Report.
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PHYSICS 125 LAB REPORT:
Name___________________________________
Convex Lenses: Ray diagrams
do = 2f
do > 2f
F
F
F
F
F
F
F
F
F
F
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Convex Lenses
Radius of curvature of spherical mirror
R = _______________
Calculation of di for object at infinity:
Experimental focal length
______________
______________
______________
Average
______________
Data Table
Determine the image distance and magnification for four cases:
Experimental values:
do
di
M
do < f
f < do < 2f
do = 2f
do > 2 f
Calculations (show work)
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Calculated values:
Percent
di
difference
Type of
image
Concave Lenses: Ray diagrams
Trace the rays on the diagrams below.
F
F
F
F
F
F
Conclusions about image locations and sizes:
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