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Diffraction experiments with infrared remote controlsJochen Kuhn and Patrik Vogt
Citation: The Physics Teacher 50, 118 (2012); doi: 10.1119/1.3677292 View online: http://dx.doi.org/10.1119/1.3677292 View Table of Contents: http://scitation.aip.org/content/aapt/journal/tpt/50/2?ver=pdfcov Published by the American Association of Physics Teachers Articles you may be interested in Novel cases of diffraction of light from a grating: Theory and experiment Am. J. Phys. 80, 972 (2012); 10.1119/1.4737854 Light intensity enhancement by diffracting structures in solar cells J. Appl. Phys. 104, 034502 (2008); 10.1063/1.2960586 Revealing the blaze angle: A simple experiment for visualizing diffraction effects using microscopic andmacroscopic gratings Am. J. Phys. 74, 649 (2006); 10.1119/1.2198890 A simple experiment on diffraction of light by interfering liquid surface waves Am. J. Phys. 73, 725 (2005); 10.1119/1.1870032 Wire Diffraction Gratings Phys. Teach. 42, 76 (2004); 10.1119/1.1646480
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118 The Physics Teacher ◆ Vol. 50, February 2012 DOI: 10.1119/1.3677292
iPhysicsLabsJochen Kuhn and Patrik Vogt, Column Editors, Department of Physics, University of Kaiserslautern (University of Technology), Rhineland-Palatinate, Germany; [email protected]
Diffraction experiments with infrared remote controlsJochen Kuhn and Patrik Vogt, Department of Physics, University of Kaiserslautern (University of Technology), Rhineland-Palatinate, Germany; [email protected] In this paper we describe an experiment in which radiation emitted by an infrared remote control is passed through a diffraction grating. An image of the diffraction pattern is captured using a cell phone camera and then used to deter-mine the wavelength of the radiation.1
The CCD chips used in digital cameras are also sensitive to electromagnetic waves in the near infrared. This property can be used to demonstrate interesting diffraction phenom-ena with simple apparatus. In addition to a cell phone with a camera function, the objects required for this experiment are an infrared remote control and a diffraction grating with a suitable line spacing (50 lines per millimeter, or so—low-cost transmission grating film works well, or even a CD used as a reflection grating).
Qualitative experimentsThe experimental setup is very simple: The user shines the
remote control onto the camera lens while holding the grating directly in front of the lens.
The diffraction pattern can be photographed using the cell phone camera (see Fig. 1) and exported to a computer to be printed and inserted into students’ lab reports. In Fig. 2 the image on the left was produced by a transmission grating hav-ing 50 lines per millimeter, and the image on the right by a cross-grating film with 900 lines per millimeter.2
Quantitative experimentsIn order to determine the wavelength of the infrared radia-
tion produced by a remote control device, the experimental setup is adjusted as in Fig. 3(a). A ruler, oriented perpendicu-lar to the grating lines and placed just above or below the ra-diation source, serves as a measuring scale.
The grating and cell phone must be positioned so that the infrared radiation hits the grating and the diffraction pattern can be seen, together with the ruler, on the cell phone screen [Fig. 3(b)]. After the photograph is taken, the wavelength of the infrared radiation can be determined using the diffraction grating equation, d sin a = nλ ,where d is the grating spacing, n
Column Editors’ Note: A number of recent papers in this journal have described the use of new mobile media technology (cell phones with cameras, smart phones, tablets, and the like) as laboratory tools for introductory physics experiments. With this issue of TPT we introduce a new column, “iPhysicsLabs,” devoted to this topic. The column will feature short papers (gener-ally less than 1000 words) describing experiments that make use of the sophisticated features of mobile media devices produced by various manufacturers. Each month, in this space, we will present examples of how students can use (often their own) devices to investigate interesting and important physical phenomena. We will publish “iPhysicsLabs” on a trial basis for a number of months; depending on reader response it may evolve into a regular TPT column.We invite readers to submit manuscripts to the column editors. The contributions should include some theoretical back-ground, a description of the experimental setup and procedure, and a discussion of typical results. Submissions should be sent to the email address given above. We look forward to hearing from you.
Fig. 1. Image of the diffrac-tion pattern on the cell phone display.
Fig. 2. Diffraction patterns produced with an infrared remote control and transmission grat-ings, recorded with a cell phone camera.
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The Physics Teacher ◆ Vol. 50, February 2012 119
Jochen Kuhn and Patrik Vogt, Column Editors, Department of Physics, University of Kaiserslautern (University of Technology), Rhineland-Palatinate, Germany; [email protected]
is the order number, and λ is the wavelength. Since the angle a is small, we can write sin a ≈ tan a = S/L (see Fig. 4).
A typical result, using a BenQ Model CT050606055 remote control, a grating having 80 lines/mm (d = 1.25 310-5 m), and L = 0.77 m, is S = 11.5 cm (for n = 2), which results in a wave-length λ = 930 nm. This value lies within the usual wavelength range for the infrared diodes used in remote controls (900 nm–1200 nm).
References1. Corresponding ideas were previously published in J. Kuhn,
P. Vogt, and S. Müller, “Neue Experimente mit dem Handy im Physikunterricht” (translated as “New Experiments with Cellphones in Physics Classroom Education”), edited by D. Höttecke, “Naturwissenschaftliche Bildung als Beitrag zur Gestaltung partizipativer Demokratie: GDCP-Jahrestagung in Potsdam 2010” (translated as “Science Education as Contribu-tion of Ideas for Creating Participative Democracy: GDCP-Annual Conference Proceedings, Potsdam/Germany 2010") (LIT-Verlag, Münster/Germany, 2011); J. Kuhn, P. Vogt, and S. Müller, “Handys und Smartphones – Einsatzmöglichkeiten und Beispielexperimente im Physikunterricht” (translated as “Cellphones and Smartphones – Capabilities and Examples of Experiments in Physics Classroom Education”), Praxis der Naturwissenschaften – Physik in der Schule (translated as "Practice of Sciences – Physics in School”), 7, 60, 5–11; F. Catel-li, O. Giovannini, and V. D. A. Bolzan, “Estimating the infrared radiation wavelength emitted by a remote control device using a digital camera,” Phys. Educ. 46, 219–222 (March 2011).
2. Cross-grating films with 900 lines per millimeter (and others) could be ordered for example from Urhammer (a German com-pany for teaching materials; see www. urhammer.de).
Fig. 3. Determining the wavelength of infrared radiation of a remote control: (a) experiment setup; b) image of diffraction pattern and ruler.
S
L
α
camera
α
grating
ruler
Fig. 4. Geometry of the experimental setup.
(a) (b)
iPhysicsLabs
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