Class Group:
S15
Lab Group’s
No:
9
CENTRE OF FOUNDATION STUDIES
FOUNDATION PHYSICS II
LABORATORY REPORT
Experiment
Name
Student ID
Lab Instructor’s Name
Date of Experiment
REFLECTION & REFRACTION OF LIGHT
SYED AMZAR BIN SYED MUSTAFA
2021201512
NOR FARIDAH HANIM BINTI MAT
JUNIT
23RD FEBRUARY 2022
Member 1
SYED AMZAR BIN SYED MUSTAFA
(2021201512)
Member 2
SUMAYYAH BINTI LOKMAN
(2021815144)
Member 3
WAN NUR FHARISA BINTI WAN
MOHAMAD ZANI (2021845722)
Marks
Comment
PHY098
REFLECTION & REFRACTION OF LIGHT
Syed Amzar Syed Mustafa
Partners: Sumayyah Lokman, Wan Nur Fharisa
Date Performed: February 23, 2022
Tutor’s/Lecturer’s Name: Nor Faridah Hanim Mat Junit
ABSTRACT
An experiment was performed to verify the law of reflection of light known as Snell’s law and
to determine the refractive index of glass block. The refractive index of glass, n2 is determined
by calculating the slope of graph sin θi versus sin θr which results in the value of 1.52. The
refractive index of air, n1 is 1.
INTRODUCTION
The processes of reflection and refraction can occur when light moving in one medium hits a
boundary then going into a second medium. In reflection, some of the light that strikes the
second medium reflects and it is called reflection. Refraction occurs when light passing through
the second medium bends at an angle to the normal to the boundary. Reflection that occurs on
smooth surfaces will result in parallel to one another and it is called specular diffusion, while
for the rough surface, it will reflect the rays in many directions. The incident and reflected rays
make angles θi and θr with a line perpendicular to the surface at the point where the incident
rays strike the surface which called as normal line.
The reflection law’s states that angle of incidence θi is equal to the angle of reflection as shown
below.
θi = θr
Refraction of light happens when a ray of light passing through a transparent medium meets
up with a boundary leading to another transparent medium, part of the ray is reflected, and the
other part enters the second medium. The light that enters the second medium is refracted when
it bends at the boundary. At the point of incidence, the incident ray, reflected ray, refracted ray,
and normal are all in the same plane. The law of refraction is known as Snell's law. The constant
in Snell's law is the ratio of the refractive indices of the two materials n and n'. The law of
refraction is usually written as below.
n1sinθ1 = n2sinθ2
Thus, this experiment is conducted in order to verify the law of reflection of light and determine
the refractive index of glass block by doing calculations.
METHODOLOGY
1. Procedure for reflection of light experiment
The mirror was placed on a sheet of paper, holding it vertically, and its outline was drawn. The
ray box was set up such that a ray of light strikes the mirror. The incident and reflected rays
were marked with crosses. The mirror was removed and marked the point of incidence. A ruler
was used to join the crosses along the lines of the ray of light. The protractor was used to draw
the normal at the point of incidence. Measure angle of incidence θi, and the angle of reflection
θr. Steps 1-7 was repeated for five different angles of incidence using the same set up.
2. Procedure for refraction of light experiment
The glass block was placed on a sheet of paper and its outline was drawn. The ray box was set
up such that a ray of light enters the glass block from the longest side. The incident and the
emergent rays were marked with crosses, and the point of incidence. The glass block was
removed, and the ruler was used to join the crosses to draw the path of the ray of light. The
protractor was used to draw the normal to the glass surface. Angle of incidence θi, and the angle
of refraction θr were measured. Steps 1-6 was repeated for five other angles of incidence.
RESULTS
Table for reflection data
Angle of incidences, θi (°)
Angle of reflection, θr (°)
10
10
20
20
30
30
40
40
50
50
60
60
Table for refraction data
Angle of incidences, θi (°)
Angle of refraction, θr (°)
n2
10
6.65
1.50
20
13.18
1.50
30
19.47
1.50
40
25.37
1.50
50
30.71
1.50
60
35.26
1.50
ANALYSIS
PART 1
Graph of θi against θr
70
60
60
50
50
40
40
θi
30
30
20
20
10
10
0
0
10
20
30
40
50
60
θr
PART 2
θi (°)
θr (°)
sinθi
sinθr
10
6.65
0.17
0.12
20
13.18
0.34
0.23
30
19.47
0.50
0.33
40
25.37
0.64
0.43
50
30.71
0.77
0.51
60
35.26
0.87
0.58
70
Graph of sinθi against sinθr
1
0.87
0.9
0.77
0.8
0.64
0.7
sinθi
0.6
0.5
0.5
0.34
0.4
0.3
0.17
0.2
0.1
0
0
1
2
3
4
5
sinθr
ANALYSIS (CALCULATION)
•
Calculation of n2 using Snell’s law formula
n1sinθ1 = n2sinθ2
n2 =
𝑛1 sin 𝜃1
sin 𝜃2
(1.00)sin⁡(10)
=
sin⁡(6.65)
• Example calculation of sinθi:
sinθi = sin 10˚
sinθi = 0.17
•
Example calculation of sinθr
sinθr = sin 6.65
sinθr = 0.12
•
Gradient of the graph
Maximum gradient:
0.77−0.64
mmax = 0.51−0.43 = 1.63
Best line gradient:
0.87−0.17
m = 0.58−0.51 = 1.52
Minimum gradient:
0.64−0.50
mmin = 0.43−0.33 = 1.4
= 1.50
6
7
•
Error of gradient
Δm =
•
mmax −mmin
2
=
1.63−1.4
2
= 0.12
Refractive index, n
1.52± 0.12
•
Percentage of precision of refractive index
Δm
m
•
0.12
⁡ × 100% = 1.52 ⁡ × 100% = 7.89%
Accuracy of refractive index in medium by experiment
% Accuracy
=
𝑛𝑒𝑥𝑝𝑒𝑟𝑖𝑚𝑒𝑛𝑡−⁡𝑛𝑡ℎ𝑒𝑜𝑟𝑦
⁡ × 100%
𝑛𝑡ℎ𝑒𝑜𝑟𝑦
1.52−1.50
⁡ × 100%
1.50
=
= 1.33%
DISCUSSION
PART 1
In part 1, a mirror is held vertically and placed on a sheet of paper. The incidence and reflected
rays were marked on the paper when the light ray strikes the mirror. The angle of incidence, θi
and angle of reflection, θr is measured using protractor. The steps are repeated for five different
angles of incidence using the same apparatus set up.
This experiment is conducted to verify the law of reflection. The law of reflection states that
when the light ray reflects from a smooth surface, the reflected angle, θr is equal to the incidence
angle, θi as shown in this equation, θi = θr. The reflective angles formed with respect to normal
lines are equal to incidence angle when measured using protractor.
When a graph of θi versus θr is plotted, a straight line is produced which is consistent with the
law of reflection. Based on the graph, The incidence angles are equal to reflected angle for
every incidence angle used.
PART 2
In part 2, The glass block was placed on a sheet of paper and its outline was drawn. The incident
and emergent angle are marked and angle of incidence, θi along with angle of reflection, θr is
measured using protractor. The steps are repeated 5 times more using 5 different angles and
same apparatus set up.
In this experiment, Snell’s Law is used to determine the refractive index of the semicircular
glass. When the light ray passes from less dense medium which has a smaller refractive index
to denser medium, the ray will bend towards normal. In contrast, when the light ray passes
from denser medium towards less dense medium, the light ray will bend away from normal.
Using Snell’s Law formula which is n1sinθ1 = n2sinθ2, the refractive index of the glass block,
n2 is calculated. The refractive index of air, n1 is constant which is 1. The refractive index
obtained from the graph is 1.52 ± 0.12.
A graph of sinθi against sinθr is plotted resulting in a straight line. The slope of the graph
obtained indicates the refractive index of the glass block which is 1.52. It is slightly different
from the actual refractive angle of the glass block which is 1.50. The result has 7.89% error.
Errors made in this experiment may be caused by a lot of factors. For instance, inaccuracies
when measuring the incidence angle which is categorized as random error. Other than that, the
laser beam might not be aligned on the track.
CONCLUSION
In this experiment, the law of reflection is proven, and the refractive index of a glass block is
determined using Snell’s law. The angle of reflection is always equal to angle of incidence
while the angle of refraction differs depending on index of refraction on two mediums.
REFERENCES
[1] light - Reflection and refraction | Britannica. (n.d.). Encyclopedia Britannica. Retrieved
March 2, 2022, from https://www.britannica.com/science/light/Reflection-and-refraction
[2] Video details - clickview library of educational videos. ClickView UK. (2021, September
24). Retrieved March 2, 2022, from https://www.clickview.co.uk/curriculumlibraries/videodetails/id=31410460&cat=3708355&library=secondary#:~:text=A%20plane%
20mirror%20forms%20the,be%20equidistant%20from%20the%20mirror .
[3] Austin, J. (2014, May 23). Experiments to illustrate the relationship between the
behaviour of light rays interacting with optical elements. Academia.edu. Retrieved March 2,
2022, from
https://www.academia.edu/6980598/Experiments_to_illustrate_the_relationship_between_the
_behaviour_of_light_rays_interacting_with_optical_elements
PRE-LAB QUESTIONS
1. State the law of reflection.
Angle of incidence equals to angle of reflection.
2. Sketch a ray diagram of a plane mirror showing the incident ray, the reflected ray, and the
normal lie on the same plane.
3. State the theoretical value of index of refraction, n of a glass.
n= 1.50
4. Sketch a ray diagram of the refraction of light as it.
(a) moves from air into glass.
Air
Glass
ϴr
ϴi
(b) moves from glass into air.
Glass
Air
ϴr
ϴi
5. By plotting a graph of sinϴ1 versus sinϴ2, what is the physical quantity represented by the
gradient of the graph?
Gradient of the graph represents refractive index of the glass.
POST LAB QUESTIONS
1. List properties of images formed by plane mirror.
A plane mirror forms the image of an object by reflecting the light rays coming from
the object that we used. The properties of image formed by plane mirrors are virtual,
erect, and same size as the object and the image also equidistant from the mirror.
2. State the relationship between incident and reflection angle for plane mirror.
Incident and reflection angle are the same for plane mirror.
3. Explain why the index of refraction is dimensionless and must be greater than or equal to 1.
Index of refraction, n is dimensionless as it is a ratio of the speed of light in vacuum
𝑐
and in a certain material, n= 𝑣. The value must be greater than or equal to 1 because
light travels the fastest in vacuum.