Names:_________________________KEY_________________________ Group:_______________
Optics Lab: Reflection, Refraction, Polarization and Thin Lenses (70pts)
SNELL’S Law (31pts)
DATA (12 pts)
Part 1: Snell’s Law (6pts)
How can you confirm the disk is set up correctly?(2pts)
The angle of incidence should equal the angle of reflection for multiple angles
Angle of Incidence
Angle of Refraction (CW) ±
0⁰
Data – should be filled in (2 pts) with some uncertainty (1pt)
Angle of Refraction (CCW) ±
What difficulties did you encounter in measuring the angle of refraction of large angles of
incidence? (1pt) The refracted beam is much more disperse (wide) and hard to measure well.
Part 2: Internal Reflection (3 pts)
Record any changes in the reflected and transmitted ray as you increase the angle of incidence.
(1pt) General description here
Record the critical angle from the clockwise and counterclockwise directions:
(1pt)θCW = ____________± ______________
(1pt)θCCW = ___________± ______________
Part 3: Brewster’s Angle (3 pts)
Record Brewster’s angle from the clockwise and counterclockwise directions:
(1pt)θCW = ___________± ______________
(1pt)θCCW = ___________± ______________
Is the reflected light plane polarized? If so, at what angle from the vertical is the plane of
polarization? Was the light still plane polarized when not at Brewster’s angle? (2pts) Yes, the light is
plane polarized (some attempt at a number) when at Brewster’s angle, but not polarized at other
angles.
DATA ANALYSIS (14 pts)
Part 1: Snell’s Law (10 pts)
Attach plots for Snell’s Law and index of refraction. Remember to clearly label the graphs and
include linear fits. Are your graphs consistent with Snell’s Law? Explain.
Plot needs to have labeled axes, units, data and a fit with parameters identified. (5 pts) Should be
consistent with Snell’s Law (1 pt)
For Part 1, you encountered difficulties measuring the angle of refraction at large angles of
incidence. How would you take this into account in the analysis of your data?
Perhaps eliminate the last point as an outlier. Use a fit where you can put error bars on each
measurement. Any attempt at some sort of answer here (1pt)
Report the index of refraction from each of these graphs. (1pt)
nCW=___________± ______________
nCCW=___________± ______________
Calculate the weighted average (show your work): (2 pts) Work shown should include equation
used.
n=___________± ______________
Part 2: Internal Reflection
Calculate the index of refraction (show your work): (2 pts) Work shown should include equation
used.
n=___________± ______________
Part 3: Brewster’s Angle
Calculate the index of refraction (show your work): (2 pts) Work shown should include equation
used.
n=___________± ______________
Discussion Questions (5 pts)
Compare your results for the index of refraction with the value of 1.49 for acrylic. Which of
your measurements is the most precise? Which is the most accurate?
Comparison (1pt). Identifying (correctly) the most precise (1pt) and the most accurate (1pt)
What is the largest source of error in the experiment? How would you improve the experiment
in the future? (2pts) Personal ideas about improvements. Largest source of error is probably
using polarizer as a test of Brewster’s angle since there are so many other sources of light in the
room that make it difficult to really tell polarization changes.
Lab: Thin Lenses (27pts)
DATA (12pts)
Part 1 Data: Ray Tracing – any general comments? (3pts)
Part 2: Optic Bench Work
Convex lens: (4 pts) for complete data set
p
up
Q
uq
Qualitatively describe what happens when p approaches f. (1pt)
As p approaches f, q approaches infinity (it becomes nearly impossible to focus the image)
What effects does the BLUE filter have on your image? Is the image sharper with or without
the filter? Does the image distance increase or decrease? (2pts) The image distance should
decrease and the image might be sharper (definitely dimmer) with only one color.
What effects does the RED filter have on your image? Is the image sharper with or without the
filter? Does the image distance increase or decrease? (2pts) The image distance should
increase and the image might be sharper (definitely dimmer) with only one color.
Analysis (6 pts)
Calculate f for each pair of measurements in the table. Find the average and calculate the
standard error. (3 pts for calculating f, 2 pts for the average and 1 pt for the average)
Discussion Questions (21pts)
Summarize your diagram from part 1 – when do you have a virtual image? When does this
occur in the real world? (3pts) Virtual images occur when inside the focal distance. In the real
world, this happens with a magnifying lens or many other examples
How accurately are you able to determine f in part 2? How can you determine f quickly for any
lens if you don’t have a light table setup and the lens isn’t labeled? (5 pts)
Comparison to actual focal length (2 pts) and general procedure of using a distant light source
so that d(object) is basically infinity so that the focal length is the image distance (3pts)
Based on observations made in part 2, what can you conclude about the dependence of the
index of refraction on the frequency of light? Does n increase or decrease with increasing
frequency? (3 pts)
The index of refraction definitely depends on the freq of light. As freq increases, n decreases.
What kinds of lenses are used in eyeglasses? Why? (3 pts) Depends on the glasses and the
particular issue that a person has. Myopia is corrected with concave lenses which compensate
by moving the distant object that cannot be seen clearly backward onto the retina. Hyperopia
is corrected with a convex lens that moves the image of a distant object forward onto the retina
(instead of being behind)
Can you use the simulation linked in the lab writeup to build a microscope or a telescope?
What designs/arrangements work best to magnify? (5pts) Yes, you can use the simulation to
build a microscope and a telescope. Good answers will give specific examples or even a screen
shot of a lens assembly design.
How would you improve these labs? (2pts) This is mostly a participation grade for this questionsome reasonable attempt to include ideas for improvements.