73.1 ppt. v.1

1. Analysis of Intensity of CD
Diffraction Pattern using
Fraunhofer Single Slit Diffraction
Karl Arwen Cereno1, Leomark Responde1, Mark Joshua Salvacion2 and Jan
Carlo Frayre3
1 Institute of Civil Engineering, College of Engineering
2 Department of Geodetic Engineering, College of Engineering
3Department of Curriculum and Instruction, College of Education
University of the Philippines, Diliman, Quezon City 1101 Philippines

2. Abstract
In this experiment, the consistency of the
formula for intensity will be analyzed. The
method to be used includes calculating the
angle of diffraction given that there is a prior
value for a given intensity. The intensity is then
plotted and the graph is compared to the
theoretical plot of the Fraunhofer Single Slit
Diffraction. The result shows that the data
follows the theory. Because of the
approximation method used in calculating for a
given intensity, errors and deviations will be
accounted accordingly.

3. Introduction
The wave nature of light can be demonstrated
clearly by observing the interference and diffraction of
light as it passes through slits. Diffraction manifests
itself in the apparent bending of waves around small
obstacles and the spreading out of waves past small
openings. (Include fraunhofer equation, and graph)
For single-slit diffraction, the slit width can be
measured using the measurements of the diffraction
pattern. If a monochromatic light approaching the
diffracting object is parallel and the image plane is at a
distance large enough compared to the diffracting
object, the situation is of the Fraunhofer Diffraction. The
intensity of the mth fringe can then be calculated.

4. METHODOLOGY
Materials:
1. Laser Source
2. Blank CD
3. Light sensor
4. Vernier LabProTM
5. Optical Bench
6. Meter stick

5. METHODOLOGY
 This experiment was conducted to verify the
functionality of the Franhoufer diffraction
equation that relates the intensity of light on the
mth order bright band and its angular distance
from the central bright band.
 Figure 1 shows the experimental set up

6. METHODOLOGY
Figure 1

7. METHODOLOGY
 The angle of incidence of the incoming light is roughly
normal to the CD.
 The plane of the screen is set parallel to the plane of the
CD.
 The intensity of the bright bands on the diffraction
pattern was measured using a light sensor.
 Measurements are recorded in Data Table 1.

8. RESULTS
Data Table 1
y
m
(cm)
-2 - - - -
-1 345 30.8 26.42
0 1361 (Gauge the ‘D’ value. Does it fit the Fraunhofer
equation????)
1 273 30.8 26.42
2 - - - -
D = 62 cm a = 1.67 μm
λ = 650 nm Io = 1361 lux

9. RESULTS
 There is a significant difference between the
measured Intensity on the m=1 band and the m=-1
band.
 The 2nd order bright bands are observable but the
intensities are not measurable using the light
sensor.

10. CONCLUSION
 The behavior of the plotted graph follows the theoretical
behavior of the I/Io vs β (figure 3).
 The function that will best fit the data points cannot be
derived due to the limits of the graphing tool (Microsoft
Excel).

11. Conclusion
(Use the measurements
to generate a plot
following the Fraunhofer
equation)
Figure 3 Intensity of the Single slit
Fraunhofer diffraction pattern

12. RESULTS
 Graph of the ratio of the mth intensity/maximum
intensity versus β/2 (phase difference)
1.2
 (Superimpose the
1
Experimental and
0.8 Theoretical graphs)
0.6
I/Io
0.4
0.2
0
-2 -1.5 -1 -0.5 0 0.5 1 1.5 2 (Factor: π)
-0.2
mπ
Figure 2

13. CONCLUSION
The values of the measured intensity was highly
affected by the following errors.
 Instrument error
 Procedural error
 Human error

14. Acknowledgements
The researchers would like to express utmost
gratitude to the National Institute of Physics of the
University of the Philippines – Diliman for the academic
support and the privilege that they have
given, especially on the use of the laboratory and the
Lab Manuals that were provided. And ultimately, the
researchers would like express gratitude to Professor
Gerold Pidemonte for his support, encouragement and
assistance in this experiment.
(Change ‘Pidemonte’ to ‘P-E-demonte’ and Add Romy
Abaniel)

15. References
1. Lab Manual Authors, Physics 72.1 Laboratory Manual, 2007
2. Young, H., Freedman, R., “Sears and Zemansky’s University
Physics: with Modern Physics” 12th ed, Chapter 36, Pearson
Addison-Wesley, 1301 Sansome St., San Francisco, CA
94111, 2008
3. Nave,C.R., “HyperPhysics”, hyperphysics.phy-astr.gsu.edu, 2010
4. Department of Physics and Astronomy, “Fraunhofer Diffraction
with a Laser Source”, The University of
Sheffield, Sheffield.ac.uk, 2008
5. Tippie, A., Lee, T., “Experiment with Diffraction”, 2008