Diffraction and Interference of Single Slit and Double
Slit for 650 nm Laser
Ethan Gale, Andrew Kim, Andrew Palm
Department of Physics and Astronomy, Augustana College, Rock Island, IL 61201
Abstract: Other searching for articles will see the title first, then if they are interested,
they may read the abstract. This is your second chance to sell what you have (the first
being the title) and frame why it is important in approximately 150 words. At minimum,
you need to give a brief summary of what you did, quoting values of experimental results
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unique. I typically come back to write my abstract after the entire paper has been written.
I. Introduction
Our main objective of this experiment was to be able to calculate the wavelength of a light source via the
diffraction and interference patterns caused by a single slit and a double slit. We were able to do this by
knowing the relevance of the diffraction patterns along a certain distance from the viewing screen to the
slits. We then could monitor the intensity of the diffractions and find where the minima occurred. Double
slits caused more complicated interference patterns such that the minima of the single slits were still
apparent, however, more minima were in between. Using equations given to us in the lab handout, such as
mλ = d*sinθ, m = 0,±1,±2,…±integer, our data analysis could then lead us to an experimental wavelength.
Our results indicate a wavelength of
II. Experimental Setup
In this experiment, we followed the simple
set up as shown by figure 1. The screen in
figure 1 is actually a light detector in the
experiment. We used a light detector in
order to find the intensities of the diffracted
light source. The light detector could be
moved a horizontal distance of 20 cm. The
Science Workshop program used a
horizontal unit of angular position rather than distance. The conversion factor was found to be 904 degrees
per 20cm. This was attained by running the program through 3 times and measuring the actual distance.
In order for the data to have the greatest efficiency, the slits and the screen needed to be perpendicular. We
used meter sticks at the edge of the table and plumbobs coming from a “perpendicular” meterstick above
these metersticks. We placed the perpendicular metersticks flush against the detector and made sure the
distances from the edge of the table to the plumbobs were the same resulting in a perpendicular detector.
The same process was done for the slits.
We were able to achieve certain intensities of the diffraction patterns with the equations
I  I0
sin 2 α
cos 2 δ
α2
Where I = intensity at angle ,
I0 = intensity at center of pattern,
 = (a/)sin, and
 = (d/)sin.
From the Science Workshop, we could plot both the single slit diffraction and the second slit diffraction on
top of each other. We could the find the difference in the minimas on each side of the main maximas. We
could then find the experimental wavelengths and compare it to the theoretical 650 nm laser.
III. Results
We used the equations given to us in the lab manual, so we were able to calculate the given data:
Our results show that for the first minima, we found a wavelength of 703.39 nm with a 8.2 % error. For the
second minima, we found a wavelength of 725.02 nm with an 11.54% error. For the third minima, we
attained an experimental wavelength of 690.5 nm with an 6.23% error.
See attached excel worksheet.
IV. Discussion
Based on our data, the experiment cannot be considered a success because the percent errors are too large.
This could be due to the inaccuracy of aliging the detector and the slit so that they were perpendicular to
each other. Additionally, when the detector was analyzing the diffraction, there weren’t very many data
points for the data collected. This could be due to sliding the detector too fast along the horizontal path. If
we did it slower, there could be more data points and thus a more accurate lab.
References
C, Vogel. Diffraction and Interference. Advanced Lab Handout. April 3, 2012.