ActivPhysics
can
help with these problems:
Activities
15.1,
15.2
Section 352:
Reflection
Problem
1. Through what angle should you rotate a mirror in
order that a reflected ray rotate through 30°?
Solution
Since
el
=
0; for specular reflection, (Equation 351) a
reflected ray is deviated by
4
=
180°

2
4
from the
incident direction. If rotating the mirror changes 81 by
hel, then the reflected ray is deviated by
A4
=
12AQ1( or twice this amount. Thus, if
A$
=
30°,
lAO1l
=
15".
Problem
1
Solution.
Problem
2. The mirrors in Fig. 3533 make a 60" angle;
A
light
ray enters parallel to the symmetry axis,
as
shown.
(a) How many reflections does it make? (b) Where
and in what direction does it exit the mirror
system?
FIGURE
3533 Problem 2 Solution.
.

Solution
The first reflected ray leaves the upper mirror at a
grazing angle of 30°, and therefore strikes the lower
mirror normally. It is then reflected twice more in
retracing its path in the opposite direction.
Sec3on
353:
Refraction
Problem
8.
In which substance in Table 351 does the speed of
.
light have the value 2.292~
lo8
m/s?
Solution
11. A light ray propagates in a transparent materid
at 15O to the normal to the surface. When it


emerges into the surrounding air, it makes a

24" angle with the normal. What
is
the refractive
index of the material?
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 Spring '05
 wurthmeir
 Physics, Snell's Law, refractive index, Total internal reflection, Geometrical optics

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