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

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.


PHYSICS 125 LAB REPORT: Name______

Convex Lenses: Ray diagrams

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: Calculated values:

do / di / M / di / Percent difference / Type of image
do f
f < do < 2f
do = 2f
do 2 f

Calculations (show work)


Concave Lenses: Ray diagrams

Trace the rays on the diagrams below.

Conclusions about image locations and sizes:

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