PASCO OS-8459 Beginning Optics System - Manual (Page 19)

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M o d e l N o . O S - 8 4 5 9 E x p e r i m e n t 7 : H o l l o w L e n s
19
Experiment 7: Hollow Lens
Purpose
In this experiment you will explore how the properties of a lens are related to its
shape, its index of refraction, and the index of refraction of the surrounding medium.
Background
A conventional lens is made of a material whose index of refraction
is higher than that of the surrounding medium. For instance, the
lenses in a pair of eyeglasses are usually made from glass or plastic
with an index of refraction of 1.5 or higher, while the air surrounding
the lenses has an index of refraction of 1.0. However, a lens can also
have a lower index of refraction than the surrounding medium, as is
the case when a hollow lens is “filled with air” and surrounded by
water. (The index of refraction of water is about 1.3.)
The hollow lens in this experiment has three sections: a plano-con-
cave section and two plano-convex sections. We will refer to these as
sections 1, 2, and 3 (see Figure 7.1).
You will determine whether each section acts as a converging or
diverging lens when it is a) filled with water and surrounded by air
and b) filled with air and surrounded by water.
Procedure
1. Before you test the hollow lens, make some predictions: For every configuration
in Table 7.1, predict whether incoming parallel rays will converge or diverge
after passing through the lens. Record your predictions in the table.
2. Place the light source in ray-box mode on a white sheet of paper. Turn the wheel
to select five parallel rays.
3. Fill section 1 with water and place the lens in front of the light source so the par-
allel rays enter it through the flat side. Do the rays converge or diverge after pass-
ing through the lens? Record your observation in Table 7.1.
Required Equipment from Beginning Optics System
Light Source
Hollow Lens from Ray Optics Kit
Box from Ray Optics Kit (with lenses and foam insert removed)
Other Equipment
Water
Paper towels
White paper
Double-sided adhesive tape
Eye-dropper (optional, for removing water from the hollow lens)
1 2 3
Figure 7.1: The hollow lens