Download SNC 2PI – REFRACTION OF LIGHT LAB

SNC 2DI – REFRACTION OF LIGHT (Snell’s Law) LAB
Purpose: To observe the refraction of light as it passes from air into Lucite (plexiglass) and to calculate the
index of refraction for Lucite.
Materials: Semi-circular piece of Lucite, polar graph paper, ray box
Procedure:
PART A:
1. Using a ruler, find the centre of the flat side of a piece of Lucite. Put a pencil mark (or dry erase
mark) at the centre point.
2. Place the flat edge of the Lucite along the horizontal 90o line of the polar graph paper (provided
by your teacher) with the center mark of the Lucite on the 0o (horizontal) line – this is the normal.
The curved portion of the Lucite should be facing the top of the graph paper.
3. Direct a single ray of light from the ray box (use the single slit adapter) at the centre mark on the
flat surface of the Lucite along the normal line. This is an angle of incidence (θi) of 0o.
4. Observe your angle of refraction where the refracted ray leaves the curved surface and crosses the
angle markers at the top of the graph paper. Record this as the angle of refraction (θR) in Table 1
(Air to Lucite) below.
5. Rotate the polar graph paper and Lucite together so that the light from the ray box is incident at
5.0 o and record the angle of refraction in Table 1. (Remember: the angle of refraction is the number
of degrees from the normal).
6. Continue increasing the angle of incidence by increments of 5.0o, measuring the angle of refraction
each time. Record your values in Table 1 below.
ALWAYS AIM THE INCIDENT RAY AT THE CENTRE POINT OF THE LUCITE.
7. Observe the angle of refraction as in step 2 and record it in the table below.
8. Repeat this process in increments of 5.0o until you get to 80.0o. For each angle, record the new angle
of refraction in the chart.
9. Calculate the sinθi and sinθR for each value and record them in Table 1. Also calculate an average
value for each of sinθi and sinθR.
Table 1: The Angles of Incidence and Refraction of Light Passing from Air to Lucite
Angle of
Angle of Refraction
Incidence (θi)
(θR)
0
5
10
15
20
25
30
35
40
45
50
55
60
65
70
75
80
85
0
AVERAGE
sinθi
sinθR
PART B:
1. Flip the Lucite over so that the curved surface is facing the bottom of the graph paper.
2. Repeat steps 3 to 9 from PART A but record your values in Table 2 (Lucite to Air).
3. Make a note in Table 2 of the angle of incidence when the angle of refraction is 90o. This is the
critical angle of incidence for light passing from Lucite to Air. You do not have to collect any more
data after this point.
Table 2: The Angles of Incidence and Refraction of Light Passing from Lucite to Air
Angle of
Incidence (θi)
Angle of
Refraction (θR)
0
5
10
15
20
25
30
35
40
45
50
0
sinθi
sinθR
AVERAGE
Discussion Questions: Answer the following questions in complete sentences.
1. When light moves from a medium of lower index of refraction to one with a higher index of
refraction, does the light bend toward or away from the normal? How is the speed of light affected?
2. When light moves from a medium of higher index of refraction to one with a lower index of
refraction, does the light bend toward or away from the normal? How is the speed of light affected?
3. If the index of refraction (ni) for air is 1.0003, what is the index of refraction (nR) for Lucite using
Snell’s Law and your average values for sinθi and sinθR: Show all of your work
4. Why is light not refracted at the curved edge of the Lucite as it passes back out into the air in
PART A or enters the Lucite in PART B? Use a diagram to help explain this.
5. a) What did you experimentally determine the critical angle (θi
from Lucite to Air (PART B)?
critical)
to be when light is refracted
b) Calculate the critical angle of light passing from Lucite to Air (using the value you calculated in
question 3 for the index of refraction for Lucite).