3B Scientific Light Box - Manual (Page 10)

10
Displacement, Parallel-sided Slab:
In the previous experiment, ‘d’ in the diagram is the displacement
of the emergent ray. For a given angle of incidence, this displacement is directly proportional to the
thickness, ‘t’ of the slab.
Allow a single ray of light to fall on the shorter side of the slab. Plot the emergent ray on the opposite
side and measure d. Also measure the length of the slab, t, and find the ratio d/t. Now, allow the ray to
strike the longer side of the slab at the same incident angle and measure d and t (in this case, width of
the slab) and find their ratio. Use other slabs of the same material and do the same. Is d/t the same in all
cases?
Apparent Depth, Parallel-sided Slab
Emergent Ray
r
2
i
2
r
1
i
1
Incident Ray
Real Depth
Apparent Depth
r
2
i
2
r
1
i
1
d
Emergent Ray
Incident Ray
t
Fig. 9
Fig. 8