Name:
Mariam
Date:
Fri Dec 22
Student Exploration: Basic Prism
Directions: Follow the instructions to go through the simulation. Respond to the questions and
prompts in the orange boxes.
Vocabulary: angle of incidence, angle of refraction, critical angle, dispersion, index of refraction, medium,
prism, refract, Snell’s law, total internal reflection, visible spectrum, wavelength
Prior Knowledge Questions (Do these BEFORE using the Gizmo.)
A prism is a transparent object that can be used to bend, or refract, light. The photo below shows what
happens when sunlight passes through a prism.
1. What do you see?
White light enters a prism and disperses into different
colours due the various wavelengths each colour has.
2. What does this indicate about the composition of sunlight?
Though the sun has white light it may also consist of various
colours such as red, orange, yellow and such, but just
appears as white to our eyes
Gizmo Warm-up
The Basic Prism Gizmo allows you to investigate how a
prism refracts light. The Gizmo shows a laser emitting a
beam of light through a triangular prism.
To begin, check that Single color beam is selected, λ is
500 nm, n is 1.50, w is 2.0, and the angle (θ) is 0°.
1. What do you notice about the path of light when it passes through the prism?
The light is refracted as it bends while exiting the prism
2. Move the λ slider to increase and then to decrease the wavelength of the beam of light.
A. How does this affect the color of the light ray?
The colour changes as the wavelength
increases. The colours get warmer each time the
wavelength increases, meaning it goes from blue
to green, then yellow orange and finally red.
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B. How does this affect the direction of the light ray?
Activity A:
Refraction and
dispersion
The angle of refraction changes as the light
bends less when it is a colour of a larger
wavelength.
Get the Gizmo ready:
● Set λ to 500 nm and n to 1.00.
● Check that w is 2.0 and θ is 0°.
Introduction: When light passes from a vacuum into a medium such as glass, it slows down. The index of
refraction (n) is equal to the ratio of the speed of light in a vacuum to the speed of light in a medium. The
index of refraction of air is very close to 1.00.
Question: What factors affect the refraction of light through a prism?
1. Observe: What do you notice about the beam of light when the n is 1.00?
When the value of n is equal to 1, then the light passes straight through the prism and does
not bend.
2. Predict: How do you think increasing the index of refraction will change the path of the light?
I believe that increasing the index of refraction (value of n) would change the path of the
beam of light as it would refract more.
3. Observe: Slowly increase n to 1.50, close to the value for glass. What happens?
The beam of light continues to bend as it begins to refract and then increasingly refracts.
4. Observe: Increase n to 1.53. What happens now?
There are now two refractive angles, the light does not exist the prism at the second boundary
anymore as it did before but rather refracts a second time and exits at a third boundary,
In this situation, the light cannot move from the prism into the air. Instead, it reflects off the surface, a
phenomenon called total internal reflection.
5. Gather data: Set n to 1.50. The Gizmo also allows you to change the width of the prism (w), the angle of
the prism (θ), and the wavelength of the light (λ). Describe the effect of each action listed below. Return the
Gizmo to its starting conditions after each trial.
Action
Effect on path of light ray exiting the prism
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Decrease w to 1.0.
The prism is now small and narrow and the beam of light
refracts less.
Increase w to 3.0.
The prism widens, the beam enters the prism then reflects off
the surface and exits and refracts at the third boundary. There
are three refractive rays.
Decrease θ to -30°.
The prism is rotated, the angles of the refractions are altered.
Increase θ to 30°.
The prism is rotated, The ray does not refract at the first
entrance into the prism.
Decrease λ to 400 nm.
The beam becomes purple/violet
Increase λ to 700 nm.
The beam becomes red
6. Summarize: Which actions caused the amount of refraction to increase?
Increasing the index of refraction will in turn increase the amount of refraction. Widening the
prism also causes the light to bend more.
Which actions caused the amount of refraction to decrease?
Decreasing the index of refraction will decrease the overall refraction. Narrowing the prism
causes the light to bend less.
7. Think and discuss: Why does widening the prism cause the beam to bend more? If possible, discuss your
answer with your classmates and teacher.
When the prism is widened, there is more medium/glass between the light beam which
causes it to slow down resulting in greater refraction/bending of the beam.
8. Observe: Return the Gizmo to its initial settings (n = 1.50, w = 2.0, θ = 0°). Select White light from the
menu at upper left. What happens when white light goes through a prism?
The light disperses into the colours of the rainbow, with white light going in the prism, red light
being inside the prism, and the rainbow colours exiting the prism.
The band of colors you see is called a visible spectrum. The ability of a prism to separate white light into a
spectrum is called dispersion. (Note: The Gizmo shows the spectrum as a collection of individual colored
beams rather than a continuous band of color that would be produced by a real prism.)
9. Explain: Why is a spectrum of colors produced when white light passes through a prism? (Hint: Think about
the effect of the wavelength of light on how much it refracts.)
When light enters the prism at a specific angle, each wavelength refracts at a different angle.
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As each colour holds a different wavelength, when the white light goes through the prism the
wavelengths refract and cause the light to disperse into the rainbow colours. This is because
each colour disperses based on its own wavelength.
Get the Gizmo ready:
Activity B:
● Select the Single color beam.
● Check that λ is 500 nm, n is 1.50, w is 2.0,
and θ is 0°.
● Turn on Show protractor.
Snell’s law
Introduction: When light crosses a boundary from one medium into
another, there are several important angles to keep in mind. One is
the angle of incidence (θi), which is the angle between the beam of
light and the normal to the boundary. (A normal is an imaginary line
that is perpendicular to the boundary.) The other is the angle of
refraction (θr), which is the angle between the refracted beam of
light and the normal.
Question: How can the angle of refraction be determined?
1. Measure: To measure the angle of incidence, do the following:
●
Drag the center of the protractor (the gray circle) to the
junction of the light ray and the prism, as shown.
●
The red line is the normal. Rotate the red line so that it is
perpendicular to the edge of the prism. (The gray line
should be aligned to the edge of the prism.)
●
Rotate the green line so that it aligns to the light beam.
What is the angle of incidence for this ray of light?
Thirty degrees
2. Measure: To measure the angle of refraction, rotate the green line so that it lines up with the light beam
inside the prism.
What is the angle of refraction for this ray of light?
One hundred and sixty degrees
3. Gather data: The index of refraction of air (n1) is 1.00, and the index of refraction of the prism (n2) can vary.
For each value of n2 in the table below, find θi and θr.
n1
n2
θi
θr
sine(θi)
sine(θr)
n1 · sine(θi)
n2 · sine(θr)
1.00
1.50
30
20
0.5
0.34
0.5
0.51
1.00
1.75
30
17
0.5
0.29
0.5
0.50
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1.00
2.00
30
15
0.5
0.25
0.5
0.50
4. Calculate: Use a scientific calculator to find the sine of each angle. Then find the product of the sine of
each angle and its associated index of refraction to complete the table.
5. Analyze: What do you notice about n1 · sine(θi) and n2 · sine(θr)?
The n1 · sine(θi) remained the same while the n2 · sine(θr) values decreased as the index of
refraction increased
6. Manipulate: This relationship is called Snell’s law:
n1 · sine(θi) = n2 · sine(θr)
Rearrange this equation to solve for the angle of refraction (θr):
θr =
sin -1 (n1 · sine(θi)) / n2
7. Practice: What will the angle of refraction be for a beam of light moving from air into a prism if the angle of
incidence is 80° and the prism’s index of refraction is 1.75?
θr =
= 34.2 degrees
8. Practice: Snell’s law also applies to situations where the beam of light is moving from the prism into air. In
this case, n1 is the index of refraction of the prism and n2 is the index of refraction of air, or 1.00.
What is the angle of refraction for a beam of light moving from a prism to air if the angle of incidence is 30°
and the prism’s index of refraction is 1.6?
θr =
= 53.1 degrees
9. Challenge: The critical angle is the angle at which total internal reflection occurs. This happens when the
angle of refraction exceeds its maximum possible value of 90°. Rearrange Snell’s law to solve for the
critical angle. (Hint: Set θr to 90° and solve for θi.)
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θi =
= 39 degrees
sin -1 (n2 · sine(θr)) / n1
10. Apply: Find the critical angle for a prism with an index of refraction of 1.50. Check your answer using the
Gizmo.
θi =
= 41.8 degrees
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