HOMEWORK 4 SOLUTIONS
GEOMETRY AND REFLECTIONS
PART A
PART B
(A) If the light strikes the first mirror at an angle
1
θ
, what is the reflected angle
2
θ
?
The law of reflection says that the angle of incidence is equal to the angle of reflection:
1
θ
=
2
θ
(B) Now, find the angle
3
θ
(shown in the new figure) in terms of
1
θ
. You can easily find
3
θ
in terms of
2
θ
, then
just substitute your expression from Part A.
1
0
2
0
3
90
90
θ
−
=
θ
−
=
θ
PART C
PART D
(C) Now, find the angle
4
θ
shown in the figure in terms of
α
and
1
θ
.
(
)
α
−
θ
+
=
α
−
θ
−
−
=
α
−
θ
−
=
θ
1
0
1
0
0
3
0
4
90
90
180
180
(D) Now, find the angle
6
θ
shown in the figure in terms of
α
and
1
θ
.
(
)
1
1
0
0
4
0
5
6
90
90
90
θ
−
α
=
α
−
θ
+
−
=
θ
−
=
θ
=
θ
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UNDERSTANDING THE PROPAGATION OF LIGHT
PART (A) and (B) What is the wavelength
λ
of light in glass, if its wavelength in air is
0
λ
, its speed in air is c,
and its speed in the glass is v?
The frequency of an electromagnetic wave stays the same as it goes from one medium to another.
The
wavelength changes to compensate for the change in speed.
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 Spring '08
 Cardenas
 Light, Snell's Law, Total internal reflection

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