3B Scientific Light Box - Manual (Page 9)

9
times) until the emergent ray is not deflected. Mark the point of incidence - this is the center of
curvature.
Shift the light-box so that a single ray strikes the same point of incidence at an angle other than 90
°.
For different incident angles, mark the rays and half-chords on a circle drawn with the point of
incidence at its center.
r
i
sin
sin
is the same as
r chord Half
i chord Half
, as both angles have the equal length hypotenuses. Hence, µ can be
calculated from the following table:
Ray no. ∠i ∠r Half-chord i Half-chord r sin i sin r
µ =
r
i
sin
sin
=
r c - h
i c - h
• Does any refraction occur at the circular face of the slab? Why/why not?
Measurement of µ - Parallel-sided Slab: Allow a single ray to fall on a parallel-sided slab at an angle
other than 90 °. The (i
1
-r
1
) angle determine the refractive index of acrylic plastic with respect to air
while the (i
2
-r
2
) angle determine the refractive index of air with respect to acrylic plastic. Measure the
values for different incident angles and calculate the mean refractive indices for both surfaces.
• What do you expect the product of the two refractive indices to be (theoretically)? What is it
actually?
• Are the incident and emergent rays parallel?
i
r
N
1
2
3
N
1
2
3
Half Chord
Semi-Circular
Slab
Fig. 7