SCORING CHECKLIST

Practicum

SFT 3023: VIBRATIONS, WAVES & OPTICS

Experiment GGO1 GGO2 GGO9

Experiment Date 30 MAY 2024
Lecture Group A B C D E F
Instructor Dr. Rosazley Mrs. Mazlina Associate Prof. Ts. Dr.
Ramly Darus Shahrul Kadri Ayop

Student ID Student’s Name

D20231107881 MOHAMMAD AMIN BIN ABDUL HADI
D20231107880 NURLEESYA AFIQAH KAMAR MOHMAD ZAKARIA
D20231107893 MABELLE RANDUS J SEDOMON
D20231105152 CHONG SUK KEI

GUIDE

1. Read INSTRUCTION carefully.

2. In the CHECKLIST section, the students may refer to important criteria
needed in their laboratory report and self-mark (✔) for criteria that have been
fully met in the report.
3. In the SCORE section, the instructor must enter a score of:

0 1
The response is unclear, the Criterion is clearly met
criterion is not fully and clearly
present, or the response is 'I don't
know' or similar.
 1 Correct title ✔
# CRITERIA SELF- SCORE 2 Correct pair of axes and units labels ✔
CHECK 3 Appropriate size/proportion ✔
(✔) 4 Correct graph fitting with equation ✔
A Title H Discussion
1 Correct title ✔ 1 Recognize dependent and independent variables. ✔
2 Name and ID ✔ 2 Correct use of information for the graph ✔
3 Experiment date ✔ 3 Correct calculation/analysis. ✔
B Abstract 4 Correct response to the inquiry. ✔
1 Correct objective(s) ✔ I Conclusion
2 Summary of procedures and apparatus used ✔ 1 State the conclusion(s) based on objective(s). ✔
3 State the result(s) ✔ 2 State one reasonable factor of result deviation from the ✔
C Keywords theory.
1 At least TWO relevant keywords stated ✔ 3 Suggest logically how to minimize the deviation in I2. ✔
D Introduction J Reflection
1 Use at least one graphics/figure of the concept. ✔ 1 At least THREE sentences for every person. ✔
2 Describe relevant concept(s) based on D1 ✔ 2 Correct language structure and spelling. ✔
3 Relevant formula(s) ✔ K Formatting – Profesional Look and Apparent
4 Relate experiment with concept(s) ✔ 1 Use given cover page and scoring checklist ✔
E Methodology 2 Justify all paragraphs alignment with appropriate ✔
1 Use own experiment diagram/photo ✔ spacing
2 Correct labelled diagram/photo 3 Italic font for symbols and regular font for units ✔
✔
3 Correct experiment description ✔
4 Consistent font and size ✔
4 Passive sentences. 5 Save file as PDF and named according to the given ✔
✔
format
5 All apparatus labelled in E2 are mentioned. ✔ TOTAL MARKS (40)
F Data
1 Table with correct caption ✔
2 Logical data ✔
3 Correct labels and units ✔
4 Correct measurement uncertainties ✔
5 Data recorded according to uncertainties (F4) ✔
6 Data written using approriate scientifc format. ✔
G Graph
 Snell’s Law
Experiment was conducted on 30th of May 2024
Abstract
The aims of this experiment is to determine the refractive index of Perspex and determine the
critical angle for the air-perspex interface. The light ray is set to different angles from the
normal line by using ray box and the light travels into the rectangular perspex then the
refraction angle is obtained is recorded. Meanwhile, using the same method semicircular
perspex is used to find the total internal reflection angle. There are two condition for the total
internal reflection to occur. Which is it needs two medium with different reflective index.
Secondly, The angle of incident must be higher than the critical angle.
Keywords: refractive index, critical angle, incident angle, light
Introduction
Light is a form of electromagnetic wave that is visible to human eye. Snell’s Law which is also
known as Law of Refraction describes how light rays change direction from a medium to
another medium with different refractive index, n. The relation between the angle of refraction
and the angle of incident is directly proportional. It can be expressed as ;

𝑛1 𝑠𝑖𝑛(𝜃1 ) = 𝑛2 𝑠𝑖𝑛(𝜃2 )
where ;
𝑛1 and 𝑛2 are the refractive index of the first and second medium.
𝜃1 is the incident angle which is an angle between incident ray and normal line.
𝜃2 is the refractive angle between refraction angle and normal line.
An example of this phenomenon is the position of a fish in an aquarium seen from the side is
slightly different from its real position seen from above.
Total internal reflection is a phenomenon that occurs when a light travel within a medium
strikes the boundary of a less dense medium at an angle that is greater than its critical angle.
As a result, the light is completely reflected back into the denser medium. The critical angle,
𝜃𝑐 is the angle of incident which total internal reflection occurs. Mathematically, it can be
calculated by using Snell’s Law by setting the angle of refraction, 𝜃2 to 90°.
𝑛1 𝑠𝑖𝑛(𝜃𝑐 ) = 𝑛2 𝑠𝑖𝑛(90°)
𝑛1 𝑠𝑖𝑛(𝜃𝑐 ) = 𝑛2
𝑛2
𝑠𝑖𝑛(𝜃𝑐 ) =
𝑛1
 𝑛2
𝜃𝑐 = 𝑠𝑖𝑛−1 ( )
𝑛1
Thus, by conducting the experiment, the refractive index of the perspex and the critical angle
for the air-perspex interface can be calculated.
Methodology
Part I
1) A borderline indicating the air as medium 1 and Perspex as medium 2 on clean white
paper is drawn. The normal is also drawn.
2) Lines with the incident angle in medium 1 𝜃1 = 10° , 20° , 30° , 40° , 50° , 60° , 70° , 80° are
drawn and labeled.
3) Starting with 𝜃1 = 10° , the ray box is set so that the light ray is on the corresponding
line.
4) The refracting ray is traced. The refracted angle is labeled and measured as 𝜃2
5) The procedure is repeated with other values of 𝜃1
6) All procedures are repeated for another two readings.
Light Source

Paper
Normal Line, n

Incident Ray, i
Center. C

Refracted Ray, Rectangular

r Perspex

Figure 2 Refractions and reflections at air-perspex interfaces to determine the index of

refraction
Part II
1) The semicircular boundary is traced.
2) The midpoint of the flat surface is marked.
3) The ray box is pointed toward the midpoint.
4) While keeping the ray toward the midpoint, the angle at which the refracted ray is no
longer visible from the Perspex toward the air and the incoming ray is totally reflected
is found.
5) Steps 3 and 4 are repeated for another two readings.
 Light Source
Paper

Semicircular
Perspex
Critical Angle

Normal Line, n

Figure 2 Refractions and reflections at air-perspex interfaces to determine the critical

angle.
𝑛𝑎𝑖𝑟 = 1.00

𝜽𝟐 (±𝟏°)
𝜽𝟏 (±𝟏°) 𝒔𝒊𝒏𝜽𝟏 Reading 1 Reading 2 Reading 3 Average 𝒔𝒊𝒏𝜽𝟐
10 0.174 6 6 7 6 0.105
20 0.342 12 11 14 12 0.208
30 0.500 19 18 20 19 0.326
40 0.643 25 24 26 25 0.423
50 0.766 31 30 31 31 0.515
60 0.866 36 35 36 36 0.588
70 0.940 40 40 40 40 0.643
80 0.985 44 45 44 44 0.695

Table 1: Data taken from Part 1

𝜽𝒄 (±𝟏°)
Reading 1 Reading 2 Reading 3 Reading 4
42 43 43 43

Table 2: Data taken from Part 2

Graph 1: 𝑠𝑖𝑛𝜃2 versus 𝑠𝑖𝑛𝜃1 from Table 1.

 Discussion
For Part 1 and from Snell’s Law,
𝑛𝑃𝑒𝑟𝑠𝑝𝑒𝑥 sin 𝜃2 = 𝑛𝑎𝑖𝑟 sin 𝜃1
𝑛𝑎𝑖𝑟
sin 𝜃2 = sin 𝜃1
𝑛𝑃𝑒𝑟𝑠𝑝𝑒𝑥
When compared to linear equation 𝑦 = 𝑚𝑥 + 𝑐 and by setting 𝑐 = 0. Therefore, the refraction
index of Perspex is obtained from the slope of the graph.
𝑛𝑎𝑖𝑟
𝑚=
𝑛𝑃𝑒𝑟𝑠𝑝𝑒𝑥
1
0.7214 =
𝑛𝑃𝑒𝑟𝑠𝑝𝑒𝑥
𝑛𝑃𝑒𝑟𝑠𝑝𝑒𝑥 = 1.39
From the consequence of the calculation is to obey Snell’s Law where the index of refraction
of the Perspex for this experiment is close to the theoretical value of the refractive index of
Perspex. Thus, the equation obtained through the gradient of the Graph 1 is clearly proved
using Snell’s Law. Which we can say that the angle of refraction and the angle of incidence is
proportional to each other. For the total internal reflection to occurs the light must be travelling
from a denser medium into a less dense medium and the angle of incidence, i must be greater
than the critical angle.
Conclusion
From the experiment, the refractive index of Perspex is is found to be 1.39 from the slope of
the graph with its linear equation sin 𝜃2 = 0.7214 sin 𝜃1 and the graph follows the Snell’s Law.
The critical angle for the air-Perspex interface is 43°. The result obtained may be deviated due
to the parallax error . To minimize the deviation, the reading is taken repeatedly, and the
average value is calculated.
Reflection

(1)I was really thrilled about this experiment because it's the first physical experiment for this
semester. (2) My groupmate's cooperation during this experiment is something I really
appreciate. (3) I gained knowledge on how to create a graph using Microsoft Excel and how to
determine the critical angle for the air-perspex interface as well as the refractive index of
perspex.
CHONG SUK KEI (D20222105152)

(1)This experiment quite simple and easy yet it is fun to do. (2) The teamwork during the
experiment is excellent, we all had chance to get hands-on experience and getting the readings.
(3) I learned the importance of precision to avoid any error and mistakes during the experiment

MABELLE RANDUS J SEDOMON (D20231107893)

(1)I think this experiment is very exciting and interesting as I gain new experience about how
to determine the angle of refraction correctly. (2) I am so grateful how cooperative and helpful
my groupmates are while doing this experiment together. (3) I appreciated each my team
members for their efforts of helping me to complete this experiment successful.

NURLEESYA AFIQAH KAMAR MOHMAD ZAKARIA(D20231107880)

(1)This experiment helped me obtain a better understanding of Snell's Law through practical
illustration. (2)I learned the value of precision, since even tiny inaccuracies can have a huge
impact on results.(3)I admire my group's efforts and cooperation, emphasising the importance
of teamwork.

MOHAMMAD AMIN BIN ABDUL HADI (D20231107881)