Lab 6: Law of Reflection and Law of
Refraction Data & Analysis
Name: Kevin Napier
Lab Partner if Relevant: Sarah Kensy
Pledge: Kevin A Napier / Sarah J Kensy
Activity I Questions:
Question 1:
A surface is polished so that it is smooth for microwaves but it is not smooth for the visible light
spectrum. Give an explanation for why the surface is considered smooth for one type of
electromagnetic wave and not another? Be specific. You may need to go back and look at the
electromagnetic spectrum.
The surface is smoother when the wavelength is longer.
Question 2:
Referring to the above question, would the surface that is smooth for microwaves also be
smooth for radio waves? Give a very brief explanation for your answer.
Yes, because radio waves have a longer wavelength than microwaves.
Part 1
Table 1: Index of Refraction of Water
Angle of
Incidence, I
Angle of
Refraction, R
Index of refraction of
water, nwater
(keep 3 digits in your answer)
20
30
40
50
60
70
80
15
23
30
35
40
45
48
Average Index of Refraction from 7 trials
1.321
1.279
1.285
1.335
1.347
1.328
1.325
1.317
Sample Calculation 1:
Show a sample calculation for determining the index of refraction of water. Make sure your
calculator is set in degrees.
nwater = nair
()
sin ( R )
sin I
N1 = N2 sin(20)/sin(15)
N = 1.321
Sample Calculation 2:
Show a sample calculation for determining the speed of light in water by using the average index of
refraction. Record your results in Table 2 below.
vwater =
c
nwater
227,790,432.8 m/s
Table 2: Record your results from above
Average Index of Refraction for
water. nwater
1.317
Speed of light in water
vwater
227,790,432.8 m/s
Calculation 3: Percentage Error in your measurement
Show a sample calculation for determining the percentage error in your measurement of the index
of refraction of the water.
% error =
1.33 - nwater
1.33
´ 100%
.98%
Part 2:
Table 3: Index of Refraction of Glass
Angle of
Incidence, I
Angle of
Refraction, R
Index of refraction of
glass, nglass
(keep 3 digits in your answer)
20
30
40
50
60
70
80
14
20
25
30
36
39
42
Average Index of Refraction from 7 trials
1.413
1.461
1.520
1.532
1.473
1.493
1.471
1.480
Sample Calculation 4:
Show a sample calculation for determining the index of refraction of glass. Make sure your
calculator is set in degrees.
nglass = nair
()
sin ( R )
sin I
N1 = N2 sin(20)/sin(14) = 1.413
Sample Calculation 5:
Show a sample calculation for determining the speed of light in glass by using the average index of
refraction. Record your results in Table 4 below.
vglass =
c
nglass
202,702,702.7 m/s
Table 4: Record above data below
Average Index of Refraction for
glass. nglass
1.480
Speed of light in glass
vglass
202,702,702.7 m/s
Calculation 6: Percentage Error in your measurement
Show a sample calculation for determining the percentage error in your measurement of the index
of refraction of the glass.
% error =
1.50 - nglass
1.50
´ 100%
1.33%
Part 3:
Table 5: Index of Refraction of Mystery Material
What is your mystery material A or B? ____A____
Angle of
Incidence, I
Angle of
Refraction, R
Index of refraction of
mystery material, nmaterial
(keep 3 digits in your answer)
20
30
40
50
60
70
80
9
12
15
19
20
23
25
2.186
2.404
2.483
2.352
2.532
2.404
2.330
Average Index of Refraction from 7 trials
2.384
Index of Refraction Table
Substance
Acetone
Sugar Solution
Fused Quartz
Crown Glass
Sapphire
Arsenic trisulfide glass
Diamond
Silicon
Index of refraction, n
1.36
1.38
1.46
1.65
1.77
2.04
2.42
3.96
Question 3: From the table of known indices of refraction, what is your best estimate for what
the mystery material is made of? Give a brief explanation for your answer.
It is most likely made of diamond because the numbers are extremely close.
Calculation 7: Percentage Error in your measurement
Show a sample calculation for determining the percentage error in your measurement of the index
of refraction of the mystery material.
nTable - nmystery
% error =
material
nTable
´ 100%
1.488%
Question 4: From what we have learned in this activity, answer the following questions and use
the table provided above.
a. Would the light travel faster or slower in crown glass as compared to water?
It would travel faster in water.
b. When light is incident from air into a second material, would the light refract (bend)
more or less in crown glass as compared to water? In other words, in which material
would you see the biggest change in the direction of the ray of light?
It would refract more in glass.
c. Two experiments are performed and the results are shown in the figures below. In
one experiment, light is incident from water into crown glass and in another
experiment light is incident at the same angle from standard glass (n = 1.50) into
crown glass. Label which figure represents the experiment with water/crown glass
and which represents the experiment with standard glass/crown glass. Give a brief
explanation for your answer.
Water or Standard Glass?
Crown glass
Figure 1
Water or Standard Glass?
Crown glass
Figure 2
Figure 1 is water and Figure 2 is glass. This is because the light is refracted more in Figure 2
than in Figure 1.
Part 4:
Table 6 Critical Angle for Substance at the boundary of Air
n1
1.40
1.50
1.60
n2
air
1.00
1.00
1.00
Critical angle
for materials in
air
q critical
45
41
39
sin (q critical )
n2
n1
.707
.656
.629
.714
.667
.625
Table 7 Critical Angle for Substances at the boundary of water
n1
n2
water
Critical angle
for materials in
air
q critical
sin (q critical )
n2
n1
1.40
1.33
72
.951
.95
1.50
1.33
63
.891
.887
1.60
1.33
55
.819
.831
Question 5: What happens to the critical angle at the boundary of air as the index of refraction
increases (n1). Review Table 6 for your answer.
As the index of refraction increases the critical angle decreases.
Question 6: How does the critical angle of a give substance compare when it is at the
boundary of air as compared to water. Consider the glass (n = 1.50), how does the critical angle
compare in air and water (Compare the results of Tables 6 & 7 for glass)?
The critical angle will be smaller for air than water.
Question 7: In general, what happens to the critical angle of a given substance like glass
when the material surround the glass changes? In other words, what happens to critical angle of
glass when the surrounding material’s index of refraction increases? (Think about what would
have happen when the index of refraction eventually equal the glass) You can play with the
simulation to see what happens by adjusting the index of refraction of the region 2.) Will this
happen to all substances as the surround material’s index of refraction increases? (Play with the
simulation to check your answer if you need some help answering this.)
When the material’s index of refraction increases the critical angle decreases. This would
happen to all materials.
Question 8: Is it possible to have total internal reflection when light travels from a region of
low index of refraction (faster speed of light) to a region of high index of refraction (slower speed
of light)? If so, use the simulation to provide proof by giving an example of the indices where this
is possible.
It is not possible to have total internal reflection when light travels from a region of low index to
a region of high index of refraction.