PASCO OS-8459 Beginning Optics System - Manual (Page 49)

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M o d e l N o . O S - 8 4 5 9 T e a c h e r ’ s G u i d e
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tual image, viewed through the eyepiece lens, coincides with the virtual image of the grid pattern viewed through
both lenses.
Further study, Increasing Magnification: As the objective lens is moved closer to the object, the eye-
piece must be moved further away. In practice, the objective can be moved to within about 13 cm before distor-
tion from lens aberrations becomes significant. The theoretical limit is 10 cm, or the focal length of the objective
lens.
Experiment 13: Shadows
When the pencil is illuminated by the point source, the shadow appears sharper than when illuminated by a dis-
tributed light source (the crossed-arrow object). When illuminated by both point sources, the pencil casts two
shadows. The area where the shadows overlap is the umbra. The areas of partial shadow are the penumbra. By
moving the pencil toward the screen, the relative size of the umbra is increased. By moving the pencil away from
the screen, the umbra is decreased until the two shadow separate entirely.