No abstract

In this work, a simple photoluminescent technique for visualization of the velocities of carts moving on a dynamics track is described. The main advantage of the method is its clear principle. It provides an intuitive visualization of the velocity at its place of incidence that is unique, especially for introductory classroom demonstrations.

Bulbs are considered to be very inefficient sources of light. Bulbs give light and heat. As we use them for a long time, especially in winter, a large part of the heat produced by bulbs lowers the power consumption of the heating system.In this paper the problem of the real efficiency of a bulb is solved when both the lighting and heating effects of illumination of the interior of buildings are taken into account. It is analysed from the viewpoints of the energy consumed and the price of that energy. The real efficiency of bulbs and the savings obtained by replacing them with fluorescent lamps are calculated for various locations.

A pair of galvo mirrors reflecting light from a laser pointer is suggested for use as a school demonstration of Lissajous figures. The device is small, cheap and easy to assemble. Combined with a two-channel waveform generator, a full spectrum of excellently stable Lissajous figures can be generated (concerning frequency ratio, amplitude ratio and initial phase angle difference). The operation at frequencies faster than the vision persistence allows us to draw the figures on a normal projection screen or on a wall. When operated with a violet laser pointer and a thermoluminescent foil, the frequencies can be decreased and the advance in figure drawing can be followed. The memory effect of the thermoluminescent foil also enables us to record and observe several Lissajous figures simultaneously.