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Unformatted text preview: ifferent optical media can be arranged
as a lens to collect and focus light. We can determine the focal length of a lens by determining the point
where parallel rays, incident on one side of the lens, will come to a focus (Figure 4). Ideally, all rays should
focus to a common focal point independent of their distance from the axis of the lens and independent of
the wavelength of the light, λ .
Select the thin plano-convex acrylic lenses pictured in Figure 5. Measure the focal length of the lens
(n ≈ 1.49) as follows:
Form a suitable set of parallel rays using the multi-ray projector by rotating the small adjustable mirrors
inside the projector. Determine that the rays are parallel to a few mm relative to the central, ﬁxed ray.
(careful: the projector may be hot!). Now place the lens perpendicular to the parallel rays and determine
the focal point relative to the center of the lens (Figure 4).
Do all rays focus to a common point? If not, record the focal length as a function of the particular
rays involved. Also, even for a set of rays that appear to come to a common fo...
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- Spring '14