Chocolate, Microwaves and the Speed of Light

Microwaves have become indispensable in research work and industry. They are used for sample preparation, extractions and for synthesis. Commercially available “kitchen microwaves” can also be used for experiments: To measure the speed of light, for example.

How is that possible?

Microwaves – like visible light – are electromagnet waves which move at a speed of 299,710 km/s. The inside of the household microwave is constructed so that a standing wave is formed. This wave is characterized by the fact that its junctions and wave crests are always in the same position. The oscillation is strongest in the wave troughs and it is here that the food in the microwave becomes particularly warm. To heat a meal uniformly it is turned continuously.

The microwave experiment

To measure the speed of light with a conventional microwave oven we need a bar of chocolate, a ruler and a microwave. In our experiment we want to determine the exact distance between two wave crests and to do this we need to take the turntable out of the microwave. The chocolate is left in the microwave under full power until you see that it melts at two or three points. For milk chocolate this will take around 15 to 20 seconds. These melted areas represent the wave crests of the standing wave.

The distance between two neighboring wave crests can be measured with the ruler. This distance is half of a wavelength. The exact frequency of a microwave is given on the type plate at the back of the device. Usually it is 2450 MHz. The wave therefore oscillates 2.45 billion times per second. The speed of light can therefore be determined using the following formula:

Speed of light = wavelength x frequency

In the experiment shown on the photo the measured distance between two points on the chocolate was seven centimeters. This gives a wavelength of 14 centimeters.

Speed of light = 0.00014 km x 2,450,000,000 Hz = 343,000 km/s

The speed of light is calculated here as being 343,000 km/s.

Microwaves in research and industry

As is the case with kitchen microwaves, microwave devices in research and industry are used for quick heating. In contrast to kitchen microwaves, however, these industrial microwaves are designed to work with extremely high pressures and temperatures. The corresponding vessels are also specially constructed to meet these requirements. These microwaves are used for sample preparation in numerous fields, for example to digest food, soil or water samples, e.g. to extract heavy metals from foods and make it possible to exactly determine the concentration of these contaminants. Another field of application is the production (synthesis) of new active ingredients in the pharmaceutical industry. Here chemical reactions are carried out inside microwaves in a controlled way under high pressure and at the highest temperatures. This results in better yields and high purity of the desired substance.

Excellent sample preparation is the prerequisite for subsequent analysis and in trace analysis in particular it is decisive in order to determine the low concentrations of contaminants and toxins present. The microwave reaction system Multiwave GO allows the analysis of even the most demanding samples. This system can also be used for chemical synthesis, i.e. to produce new reaction products. Multiwave PRO provides a comprehensive list of accessories which allows digestion, leaching, oxygen combustion, solvent extraction, drying, evaporation, UV digestion and synthesis reactions in different scales.

  Learn more @ Anton Paar

Literature: “How to Fossilize Your Hamster: And Other Amazing Experiments for the Armchair Scientist” Mick O’Hare, Holt Paperbacks, January 2008, ISBN-10: 0805087702

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