PASCO OS-8536 OPTICS TABLE - Manual (Page 18)

14
Optics Table 012-06557A
Rhombus
Light Source
Convex
Lens
d
t
Figure 9.2
Trace the outline of the of the Rhombus and trace the rays diverging from the
surface facing away from the Light Source.
Remove the Rhombus, turn off the light source, and trace the diverging rays
back into the outline of the Rhombus. The place where these rays cross (in-
side the outline of the Rhombus) is the apparent position of the “bottom” of
the Rhombus when viewed from the “top”.
Measure the apparent depth, d, and the thickness, t. Calculate the index of
refraction of the material using n = t/d. Compare the measured value to the
accepted value (n = 1.5).
PART II
Theory
Parallel rays passing through a Convex Lens cross at the focal point of the
lens.If a block with parallel sides is placed between the lens and the focal
point, the point where the rays cross moves further from the lens.Since the
thickness, t, of the block has an apparent depth, d, that is less than the thick-
ness (d = t/n), the point where the rays cross must move by an amount equal
to the difference between the actual thickness of the block and the apparent
thickness of the block. Thus the distance, x, that the focal point moves is given by x = t - t/n, where n is the
index of refraction of the block.
Procedure
Mark the place where the two light rays
cross. Place the Rhombus between the
lens and the place where the rays cross.
Mark the new place where the rays cross.
Move the Rhombus to a new position,
closer to the lens. Does the position of the
focal point change?
Turn off the light source and measure the
distance, x, between the marks.
Using the thickness, t, of the Rhombus
from Part I and the distance x, calculate
the index of refraction using
n =
1
1 – x
t
Compare the measured
value to the accepted value (n = 1.5).
P
A
TTERN
COLOR
5 3 1
RA
Y
SLITS
Figure 9.3
New focus
with Rhombus
in place
Light
Source
Lens
Rhombus
Focus without
Rhombus