REFLECTION AND REFRACTION OF LIGHT

Course: PHY161
Section: 17250

Student Name: Javier Santos

Lab Partner: Henry Yang

Instructor: Victoria Paukova

Experiment Performed: 04/28/2024

Report Written: 05/15/2024
Objective:
To understand the phenomena of reflection and refraction of light, and to verify
experimentally the laws of reflection and refraction.
Task 1: Measure the angles of incidence and reflection and verify the law of reflection.
Task 2: Measure the angles of incidence and refraction and verify the law of refraction.
Task 3: Measure the index of refraction of glass and water.
Task 4: Measure the angle of total internal reflection for glass and water.
Task 5. Verify Snell’s law using the method of light beam shift.

Theory:
Reflection is the phenomenon where light rays bounce off a surface. According to the law
of reflection, the angle of incidence ( 𝜃 i ) is equal to the angle of reflection ( 𝜃r ). This law can
be mathematically expressed as: 𝜃i = 𝜃r
This principle holds for both flat and curved surfaces, making it fundamental in
understanding how light interacts with different materials.

While as for Refraction, Refraction occurs when light passes from one medium into
another, causing a change in its speed and direction. This bending of light is described by Snell's
Law, which relates the angle of incidence (𝜃𝑖) and the angle of refraction (𝜃r ) to the indices of
refraction of the two media (𝑛1 and 𝑛2): n1sinθi = n2sinθr

The index of refraction ( 𝑛 ) of a medium is the ratio of the speed of light in a vacuum (𝑐)
to its speed in that medium ( 𝑣 ): 𝑛 = 𝑐 / 𝑣
When light travels from a less dense medium (e.g., air) to a denser medium (e.g., glass or
water), it slows down and bends towards the normal. Conversely, when it moves from a denser
to a less dense medium, it speeds up and bends away from the normal.

This lab aims to verify the law of reflection and Snell's Law of refraction through
experimental measurements. By measuring the angles of incidence and reflection, we can
confirm the law of reflection. Similarly, by measuring the angles of incidence and refraction for
different materials, we can verify Snell's Law and calculate the indices of refraction for acrylic
and water. Additionally, we will demonstrate total internal reflection by measuring the critical
angle.
Method:

1. Apparatus used in this Experiment:

• Laser kit
• Ruler, protractor, fine point pencil and color pencils
• 360 protractor paper
• Masking tape
• LED lamp
• Beaker with clean water

2. Experimental Setup:
2.1. The first experimental setup me and my lab partner did was to listen to the demo
and instructions from the Professor.
2.2. After the demo, we then proceeded to set up the apparatus for part 1 and part 2 of
the experiment.
2.3. Wait for the professor’s instruction before starting the experiment.

3. Procedure:
First, we set up and placed a sheet of graph paper on a flat surface, securing it
with tape to prevent movement. For Part 1, we used a ray box or laser to shine a single
beam of light at a specific angle onto a flat mirror placed on the graph paper. We traced
the incident ray and the reflected ray with a pencil. Then, we measured and recorded the
angles of incidence and reflection. In Part 2, we placed a prism on the graph paper and
shone multiple beams of light from the ray box at different angles onto one side of the
prism. We traced the incident rays and the refracted rays exiting the prism, measured and
recorded the angles of incidence and refraction, and noted the bending of light due to
refraction to verify Snell's law. For Part 3, we used a semi-circular prism and shone a
light beam towards the flat side of the prism. We adjusted the angle of incidence until the
light ray reflected entirely within the prism without refracting out, indicating total
internal reflection. We traced the path of the light beam inside the prism and recorded the
critical angle at which total internal reflection occurred. In Part 4, we filled a rectangular
glass container with water and placed it on the graph paper. Then, we shone a light beam
from the ray box into the water at different angles. We traced the path of the light beam
entering and exiting the water, measured and recorded the angles of incidence and
refraction in the water, and compared the observed angles with the theoretical values
calculated using the refractive index of water. Finally, we concluded by summarizing the
observations, comparing the experimental results with theoretical predictions, discussing
 any discrepancies and possible sources of error, and reflecting on the principles of
reflection and refraction and their verification through the experiment.

Data Collection and Calculations:

Figure 1. Verifying the law of reflection

Figure 2. Measuring the index of refraction of acrylic

Figure 3. Measuring the index of refraction of water
Figure 4. Verifying Snell’s Law
Discussion and Conclusion:
The experiment on reflection and refraction of light provided important insights into the
behavior of light as it interacts with different surfaces. By using a ray box and a mirror, we were
able to visually trace the paths of incident and reflected rays, confirming the law of reflection
which states that the angle of incidence is equal to the angle of reflection.

Our key observations included the behavior of light at reflective surfaces, where we noted
the equal angles of incidence and reflection. In the refraction part of the experiment, using a
prism, we observed how light bends when passing from one medium to another, verifying Snell's
law. We also explored total internal reflection using a semi-circular prism. By gradually
increasing the angle of incidence, we reached a point where the light no longer refracted out of
the prism but instead reflected entirely within it. This critical angle observation underscored the
concept of total internal reflection, crucial for applications like fiber optics.
 Finally, we investigated the refraction of light in water, noting the bending of light rays
as they entered and exited the water-filled container. The angles of incidence and refraction were
measured and compared with theoretical values, showing good agreement and validating our
understanding of the refractive index.

In conclusion, the experiment on reflection and refraction of light provided a

comprehensive visualization of how light interacts with different surfaces and mediums. The
consistent patterns observed reaffirmed the fundamental principles of light behavior, enhancing
our understanding of optical phenomena and their practical applications.

Questions:
1. At the interface of two transparent media, a light ray experiences both refraction and
reflection. Does the angle of reflection depend on the angle of refraction?
The angle of reflection does not depend on the angle of refraction because
according to the law of reflection, the angle of reflection is always equal to the angle
of incidence, regardless of the refraction that occurs. On the other hand, the angle of
refraction is determined by Snell's law, which relates the angles of incidence and
refraction to the refractive indices of the two media. Therefore, while both reflection
and refraction occur at the interface, the angle of reflection is independent of the
angle of refraction.

2. Can you demonstrate the effect of total internal reflection using the rectangular block?
Explain your answer and support your answer with a drawing.
Yes, Total internal reflection occurs when the incident ray is greater than a
particular angle called the critical angle. When the incident ray is greater than the
critical angle then we can see total internal reflection in the rectangular block.
3. In which case the shift of the light beam passing through the transparent block equals
zero?
If light falls on the glass slab with angle of incidents as zero i.e. if light falls
on glass slab normally. Then shift of beam is zero

4. If you increase the width of the transparent block, would the lateral displacement
increase or decrease? Would changing the length of the transparent block affect the
lateral displacement?
The Lateral displacement is directly proportional to the width of the glass
slab . So if you increase the width then lateral displacement will increase.
5. New York and Chicago are 1170 km apart. There is a fiber optic link between them
with a refractive index of 1.44. There is also a satellite in orbit above at an altitude of 550
km. Assuming that the satellite is exactly midway between the cities and there are no
other communication delays in the electronics, which route would provide the fastest data
link?