Lesson 5.1 Homework Solutions
1.
If light is incident from air into water at an angle of incidence of 30
o
, what is the angle of
refraction in water if the refractive index of water is 1.33?
Solution
Angle of incidence
θ
1
= 30
o
, refractive index of air n
1
= 1, n
2
= 1.33
1
2
2
1
sin
sin
n
n
θ
=
1
2
1
2
1
sin
sin
sin 30
0.376
1.33
o
n
n
=
⋅
=
×
=
θ
2
= sin
1
(0.376) =
22
o
2.
If light is incident from water into air at an angle of incidence of 30
o
, what is the angle of
refraction in air if the refractive index of water is 1.33?
Solution
Angle of incidence
θ
1
= 30
o
, refractive index of water n
1
= 1.33, n
2
= 1
1
2
2
1
sin
sin
n
n
=
1
2
1
2
1.33
sin
sin
sin 30
0.665
1
o
n
n
=
⋅
=
×
=
θ
2
= sin
1
(0.665) =
41.7
o
3.
The spiral galaxy in the Andromeda constellation is 2 × 10
19
km away from the earth. What is this
distance in light years?
Solution
A light year is the distance light will travel in one year. The speed of light in free space is c = 3
×
10
8
m.s
1
.
One light year = 3
×
10
8
m.s
1
×
3600 s
×
24
×
365 = 9.46
×
10
15
m = 9.46
×
10
12
km
1
6
9
12
2 10 km
Number of light years
9.46 10 km
2.1 10
×
=
×
×
=
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View Full Document4.
If the refractive index of water is 1.33 and that of glass is 1.5, find the speed of light in water and
in glass.
Solution
Speed of light in free space
Refractive index
Speed of light in the medium
=
8
8
1
1
3 10 m.s
Speed of light in water
1.
2.26 10 m
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 Spring '11
 George
 Physics, Work, Light, refractive index, Total internal reflection

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