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Regenbögen, Halos, Koronen, Himmelsfarben – es gibt eine Vielzahl farbenprächtiger Phänomene in der Natur, verursacht durch Reflexion, Brechung oder allgemein gesprochen durch Streuung des Lichts an Wassertropfen, Eiskristallen oder Aerosolen. Das farbige Glitzern einer Schneeschicht scheint zunächst anderer Natur zu sein, lässt sich aber auf analoge Weise erklären.
Ein einfacher physikalischer Zaubertrick besteht darin, eine Kette über den Handrücken zu legen und danach von unten einen Ring über die Kette zu schieben. Der Ring kann entweder von der zweiten Hand oder der die Kette haltenden Hand gehalten werden. Er wird sodann losgelassen und soll (mit einem Knoten) in der Kette hängen bleiben.
The content of a student lab course is described which deals with characterization of the most important parameters governing the performance of infrared cameras. In detail, the parameters describing the temperature resolution, spatial resolution and time resolution of commercial IR cameras are analysed using simple lab experiments. Understanding the respective performance of the system is the prerequisite for applying infrared thermal imaging to quantitative measurements in physics and technology.
The physics behind the sometimes strange effects and 'unnatural' appearance of near-infrared (NIR) photographs is discussed in terms of reflection, absorption and transmission of NIR radiation with the respective objects. Besides discussing how NIR cameras work, several visible and NIR photograph pairs are presented, which include vegetation, natural water, clouds, the sky, and humans. In addition, some physics-oriented experimental NIR images are presented which clearly demonstrate some of the basic physics behind some of these awesome sights.
nfrared spectrometry is one of the most important tools in the field of spectroscopic analysis. This is due to the high information content of spectra in the so-called spectroscopic fingerprint region, which enables measurement not only of gases, but also of liquids and solids. Today, infrared spectroscopy is almost completely dominated by Fourier transform infrared (FTIR) spectroscopy. FTIR spectroscopy is able to detect minute quantities in the ppm and ppb ranges, and the respective analyses are now standard tools in science as well as industry. Therefore FTIR spectroscopy should be taught within the standard curriculum at university to physicists and engineers. Here we present respective undergraduate laboratory experiments designed for students at the end of their third year. Experiments deal first with understanding the spectrometer and second with recording and analysing spectra. On the one hand, transmission spectra of gases are treated which relate to environmental analytics (being probably the most prominent and well-known examples), and on the other hand, the focus is on the transmission and reflection spectra of solids. In particular, silicon wafers are studied—as is regularly done in the microelectronics industry—in order to characterize their thickness, oxygen content and phonon modes.
Infrared
(2013)
A cone of light appears in a tank of water when a laser pointer shines through the water onto a white piece of paper upon which the tank is sitting. We describe how students can understand the origins of this cone by constructing multiple explanations, then proposing and designing experiments to test their explanations. This process is the foundation of the Investigative Science Learning Environment (ISLE) framework, designed to engage students in the reasoning activities similar to those that physicists use to construct and apply new knowledge. We describe typical student ideas and provide a list of equipment and suggestions for facilitating student exploration relating to optics. We also explain the formal physics behind the phenomena that are involved in the experiment. Finally, we suggest how the ISLE framework can be used to help instructors find problems and experiments that engage students in devising and testing multiple explanations.
Rohe Eier oder wassergefüllte Christbaumkugeln platzen beim Eindringen des Projektils einer Luftpistole. Dieser Vorgang lässt sich einfach durch die sehr geringe Kompressibilität des Wassers und eine damit verbundene starke Druckerhöhung erklären (Physik in unserer Zeit 2013, 44(5), 251). Eine genaue Analyse aller Vorgänge sollte aber auch Fragen beantworten wie: Spielen vorhandene Luftblasen in der Flüssigkeit eine Rolle? Wie lange dauert es bis zum Aufplatzen, und muss die wassergefüllte Kugel eigentlich fest verschlossen sein?
Abstract
The brilliant visible colors of various hot springs and pools in Yellowstone National Park are explained with a combination of scattering from the water and from microbial mats that coat the bottoms of these thermal features. A simple 1D radiative transfer model was used to simulate the colors recorded in visible photographs and the spectrum of light making up these colors. The model includes attenuation in water by absorption and molecular scattering as well as reflection characteristics of the microbial mats and surface reflection of the water. Pool geometries are simulated as simple rough cones scaled to have depths and widths that match published data. Thermal images are also used to record the spatial distribution of water skin temperature. The measurements and simulations confirm that colors observed from shallow-water features arise primarily from the spectral properties of the microbial mat, which is related to the water temperature, while colors observed from deeper water arise primarily from the wavelength-dependent absorption and scattering in the water.
Abstract
Simultaneous visible and long-wave infrared (IR) images of the Moon were used with a simple energy-balance model to study the spatial pattern of lunar surface temperatures. The thermal images were obtained with a radiometrically calibrated, compact, low-cost, commercial IR camera mounted on a small telescope. Differences between the predicted and measured maximum Moon temperatures were used to determine the infrared optical depth (OD), which represents the path-integrated extinction of an elevated layer of wildfire smoke in the atmosphere. The OD values retrieved from the IR Moon images were combined with simultaneous OD measurements from a ground-based, zenith-pointing lidar operating at a wavelength of 532 nm to determine an IR-to-visible OD ratio of 0.50±0.18 for moderately aged wildfire smoke aerosol.
© 2014 Optical Society of America
Visible and invisible mirages: comparing inferior mirages in the visible and thermal infrared
(2015)
Abstract
Visible (VIS)-light and thermal infrared (IR) inferior mirages in the 8–14 μm waveband have been observed simultaneously for the takeoff and landing of various airplanes at distances of several kilometers. Similarities as well as differences between the VIS and IR mirages are discussed.
© 2014 Optical Society of America
abstract
A large part of photonics research and development, as well as commercial applications such as optical data transmission or infrared thermal imaging, occurs in the infrared spectral range between 0.8 μm and 15 μm. However, relatively little material is so far available for experimentally teaching the physics and optics of this spectral range. We report a respective new approach in the near infrared (NIR) range between 0.8 μm and 1.7 μm that allows visualization of a number of fascinating physics phenomena. First, we use the near-infrared sensitivity of silicon-based detectors in rather inexpensive video cameras and digital single-lens reflex cameras by removing the infrared-blocking filter and replacing it with a visible-radiation blocking filter. Second, we utilize modern NIR cameras based on InGaAs detectors. With both camera types we illustrate and explain a number of physics concepts that are especially suitable for curricula in optics and photonics. Examples include the strangely bright appearance of vegetation, contrast enhancement between clouds and sky, the initially surprising differences of optical material properties between the VIS and NIR range, the possibilities of visualizing buried hidden structures and texts, and recent medical applications to locate blood vessels below the skin. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
abstract
Nature provides many beautiful optical phenomena that can be used to teach optical principles. Here we describe an interdisciplinary education project based on a simple computer model of the colors observed in the famous thermal pools of Yellowstone National Park in the northwestern United States. The primary wavelength-dependent parameters that determine the widely varying pool colors are the reflectance of the rocks or the microbial mats growing on the rocks beneath the water (the microbial mat color depends on water temperature) and optical absorption and scattering in the water. This paper introduces a teaching module based on a one-dimensional computer model that starts with measured reflectance spectra of the microbial mats and modifies the spectra with depth-dependent absorption and scattering in the water. This module is designed to be incorporated into a graduate course on remote sensing systems, in a section covering the propagation of light through air and water, although it could be adapted to a general university optics course. The module presents the basic 1-D radiative transfer equation relevant to this problem, and allows them to build their own simple model. Students can then simulate the colors that would be observed for different variations of the microbial mat reflectance spectrum, skylight spectrum, and water depth. © (2015) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Bouncing Poppers
(2015)
Abstract
Toys are known to attract interest in physics and they are therefore often used in physics teaching of various topics. The present paper deals with a simple toy, the so-called “hopper popper,” which, similar to superballs, can be used when teaching mechanics. We suggest some experiments and describe the basic physics of this toy, also providing background information for teachers.
Abstract
A very old and well-known magical trick is the so-called tablecloth pull. A table is covered with a tablecloth, on top of which are certain objects. The task is to remove the tablecloth while the objects—which must not be touched—stay on top of the table. This article describes the physics behind the experiment, and presents examples recorded with high-speed cameras.
Flickering lamps
(2015)
Abstract
Many processes in electromagnetism vary with time. Some of them are well known, in particular those related to line frequencies of 50 Hz or 60 Hz such as fluctuating light output of discharge and incandescent lamps. The flickers of discharge and incandescent lamps have quite different physical principles involved, which are investigated experimentally using high-speed cameras and theoretically using simplified models. The topic is related to other phenomena such as the transient behaviour of phosphor layers covering the screen of oscilloscopes and the time-varying Lorentz force acting on the filament of light bulbs. All studies are well suited for teaching selected aspects of electromagnetism and light at undergraduate level at university.
Light-emitting pickles
(2015)
Abstract
We present experiments giving new insights into the classical light-emitting pickle experiment. In particular, measurements of the spectra and temperatures, as well as high-speed recordings, reveal that light emission is connected to the polarity of the electrodes and the presence of hydrogen.