PASCO OS-8459 Beginning Optics System - Manual (Page 23)

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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 9 : A p p a r e n t D e p t h
23
Experiment 9: Apparent Depth
Purpose
In this experiment, you will use two different methods to measure the apparent depth
of the acrylic rhombus. You will also determine the index of refraction of acrylic by
comparing the apparent depth to the actual depth.
Theory
Light rays originating from the bottom surface of a block of
transparent material refract at the top surface as the rays
emerge from the material into the air (see Figure 9.1). When
viewed from above, the apparent depth, d, of the bottom sur-
face of the block is less than the actual thickness, t, of the
block. The apparent depth is given by
(eq. 9.1) d = t/n
where n is the index of refraction of the material.
Part 1: Parallax Method
Background
Place this page flat on the table in front of you. Hold a pencil horizontally a few centi-
meters above the paper. With one eye closed or covered, look down at the pencil and
move your head side to side (without moving the pencil). Notice how the pencil
appears to move relative to the words printed on the paper; this phenomenon is known
as parallax. Now hold the tip of the pencil on the paper and check for parallax. When
there is no parallax between to objects, they are at the same distance from you.
Procedure
1. Place a blank sheet of paper flat on the table. Use a straight edge and pencil to
draw a vertical line on the paper. Place the rhombus on the paper over the line as
shown in Figure 9.2.
Required Equipment from Beginning Optics System
Light Source
Rhombus from Ray Optics Kit
Convex Lens from Ray Optics Kit
Mirror from Ray Optics Kit (used to block rays)
Other Required Equipment
Metric ruler
White paper
Very sharp pencil
n
air
= 1
n > 1
d
t
n > 1
d
t
bottom
top
Figure 9.1