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Experiment #11
Refraction
Gulyamov, Moisey
Partner’s name: Colin Johnson
Experiment Date: 04/27/2017
Due Date: 05/04/2017
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Introduction
The purpose of this experiment was to study refraction of light at different plane surfaces. When
a ray of light propagates from a medium in which its speed is v1 to another medium in which its
speed is v2,v2 is not equal to v1, and the ray of light will change its direction of motion. Thus, the
speed of light depends on the medium through which it travels. In the first part of the experiment
we placed a glass pentagon approximately at the center of the sheet of unlined paper and
carefully traced its outline with a sharp pencil. We then directed a laser light at an arbitrary angle
with the normal, making sure that the incoming incident ray was parallel to the refracted ray. We
also had to choose an angle carefully so the refracted ray would leave the square part of the glass
slab. In general, the speed of light in a given medium, v, is determined by the medium’s index of
refraction, n, defined as follows v=c/ n. Where n, according to the Snell’s Law can be expressed
as: n1sin ϴ1 = n2sin ϴ2; where sin ϴ1 is the angle made by the incidence ray with the normal to
the boundary surface, and sin ϴ2 is the angle made by the refracted ray with the surface.
Combining both equations, we can express an index of refraction as n = c/v = sin ϴi/ sin ϴr. In
the next step we again traced the outline of the glass pentagon on another sheet of paper, and
directed laser light to the apex of the triangular part of the glass slab. We then traced the
direction of the refracted light, sketched on the paper and measured the angles of incidence and
refraction, as well as the angle of deviation, by extending the incident and emergent rays. When
a ray of light passes through a prism of angle A, it is deviated from its original direction by an
angle D which has a minimum value Dm when the angle of incidence is equal to the angle of
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emergence. When the angles A and Dm are known, the following equation may be used to
determine index of refraction, n, for the material of the prism: n= sin (Dm+ A)/2)/sin(A/2). In the
last part of the experiment, we determined the index of refraction of water by using a metal
frame carrying four brass sliders 1,2,3, and 4. Following the instructions, we mounted the metal
frame on the jar with water so that the brass sliders appeared in line when looking at the first
slider A. We then removed the frame and traced the positions of the sliders on the sheet of paper.
We were able to draw the incident ray (AB) and the emergent ray (BD) and also measure the
angles of incidence and refraction.
Original Data Sheets
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Data Analysis
In the first part of the experiment we placed a glass pentagon approximately at the center of the
sheet of unlined paper and carefully traced its outline with a sharp pencil. We then directed a
laser light at an arbitrary angle with the normal, making sure that the incoming incident ray was
parallel to the refracted ray. During this step, we measured both angles of incidence and both
angles of refraction to be 22.5° and 14.5°, respectively. In the second part we directed the laser to
the triangular part of the glass slab. We then traced the direction of the refracted light, sketched
on the paper and measured the angles of incidence and refraction, as well as the angle of
deviation, by extending the incident and emergent rays. Using a protractor, we found the angle of
deviation to be 62°. With this value and the value of A being 75° we were able to calculate the
refractive index of a glass prism to be 1.5283. In the third part, found the refractive index of
water using the metal frame, carrying four brass sliders 1,2,3, and 4, provided to be 1.231. We
also found the velocity of light in a glass medium and then in a water medium. Those values
were V(water) = 2.48*108m/s and V(glass) =1.96*108m/s. With these values we were able to
calculate the index of refraction of the glass pate relative to water to be 1.22.
Conclusion
In this experiment we were able to observe experimentally the behavior of the light in different
media. We were able to calculate indexes of refraction in glass and water, and our results were
relatively consistent with the theoretical values (7.52% deviation from the theoretical value of
water refraction index). This error can be attributed to the random errors, as we might have lined
the brass sliders in part 3 not precisely enough. Furthermore, when tracing the emergent rays in
other parts of the experiment, we could not completely eliminate the human error, thus sketching
the refracted rays at the angles slightly different from the desired ones, since we need more
experience in directing properly and tracing the laser light through different media. At last, our
glass pentagon did not have an ideal surface, there were indentations all over it, which would
cause the emergent rays deviate from the expected angles, and therefore produce inaccurate
results.
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Questions
1. What cause, other than experimental error, will make the emergent ray not parallel
to the incident ray, in Part (1)?
As aforementioned, if the surface of the glass was uneven, then the emergent ray would not be
parallel to the incident ray, since the refraction angles of the ray entering the glass and the ray
entering the air, would not cancel out.
4. If a hunter desired to shoot a fish whose image could be seenin clear water, should
he aim above or below the fish? Explain by the aid of a diagram.
The hunter should aim below the image of the fish due to the refraction of light which occurs
from the water to air medium. Due to this refraction of light the fish, will appear higher in the
water than it actually is.
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6. Compute the displacement of the incident ray in Part (1).
