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Diffraction revisited : position of diffraction spots upon rotation of a transmission grating
(2005)
The question of how the line spectrum of atoms is transformed into the continuous spectrum of thermal radiation of a gas by repeated absorption and emission of photons is addressed. We consider a simple model of a hydrogen-like gas in thermal equilibrium where only the Lyman-α transition is allowed and calculate the spectra for increasing thickness of the gas. The transition from line spectra for optically thin samples to the spectra of thermal radiation for optically thick samples is demonstrated. We estimate the emissivities for hot gases and study the line width of spectral lines due to self-absorption processes.
Don't put metal objects in the microwave' is common safety advice. But why? Here we describe demonstration experiments involving placing household metallic objects in a microwave oven. These allow a better understanding of the interaction of microwaves with materials. Light bulbs and discharge lamps can also be used in instructive demonstrations.
Microwave ovens can be used to perform exciting demonstrations that illustrate a variety of physics topics. Experiments discussed here show superheating, visualize the inhomogeneous heating that takes place in a microwave and also show how to use a mobile phone to detect radiation leaking from the oven. Finally eggs can give some spectacular (though messy) explosions. In all cases please note the safety advice given.
This article forms the second of two papers on the subject of microwave cookers. In the first paper Michael Vollmer describes the physics behind the production of microwaves in the magnetron of the oven, the waveguide and the interaction between the microwaves and the food. This article looks at the physics of cooking, and how the appliance and the food industries have developed products which are now part of many of our students' lifestyles. We include many interesting demonstrations that illustrate this history and which could be used to teach many principles of physics.
This is the first of two articles about the physics of microwave ovens. This article deals with the generation of microwaves in the oven and includes the operation of the magnetrons, waveguides and standing waves in resonant cavities. It then considers the absorption of microwaves by foods, discussing the dielectric relaxation of water, penetration depths of electromagnetic waves in matter and, in considering the possible chemical changes during the microwave heating, multi-photon ionization or dissociation.
An inquiry among national experts on physics education research and teaching has been carried out using a questionnaire that deals with the organization of physics teacher training and the main tasks and research activities of professionals in physics education. The goal was to collect data on a European scale on physics teacher training at universities by professionals as well as on research activities by professionals in the field of physics education. Results are presented based on answers from 22 European countries.
Twice in a blue moon
(2009)
The surface to volume ratio in thermal physics: from cheese cube physics to animal metabolism
(2008)
Measurements of illuminance during a solar eclipse are presented. The data are compared to theoretical predictions, based on a geometrical model for obscuration. The model assumes a straight and uniform motion of the sun and moon as well as a spherical shape of both, i.e. it neglects any effects of limb darkening. Furthermore, the sun's disk is assumed to have homogeneous luminosity, i.e. any luminosity variations due to sun spots are neglected. Input parameters are the duration of the eclipse, the duration of totality, the impact parameter, i.e. the distance between the two trajectories of sun and moon, and the sizes of sun and moon. The model applies to all types of eclipses, partial, annular and total.