Meldesche tube
The Meldesche tube (also known as Meldesches capillary barometer) is an instrument that is used in physics to determine the relationship between the volume and the pressure of gases ( Boyle-Mariotte's law ) and the relationship between the volume and the temperature of Measure gases ( Charles's law ).
Today, the Meldesche tube is almost completely replaced by the similarly functioning gas thermometer , as this has a larger enclosed volume and accordingly has a higher measurement accuracy.
functionality
The Meldesche tube consists of a glass tube with a capillary inside diameter that is partially filled with mercury. The glass tube is fused shut at one end and marked with a millimeter-precise scale. The lower phase consists of air , the upper phase of mercury .
The weight of the mercury column creates a pressure which , in addition to the air pressure, also acts on the trapped air column . The mercury column must be long enough to build up such a strong pressure that the measurement can be read precisely. If you vary the pressure while keeping the temperature and the amount of substance constant, you can use the Meldesches tube to determine the functional relationship between the pressure and the length of the air column and thus indirectly the relationship with the volume.
To determine the relationship between temperature and volume, the Meldesche tube is heated at constant pressure and a constant amount of substance. Due to the higher temperature of the air column, it expands, so that one can determine the functional relationship between the length and, indirectly, the relationship between the volume and the temperature.
Didactic importance
The Meldesche tube is mainly used today in physics lessons (it is part of the physics collection of KRÖNCKE Dr. H. OHG.), As it delivers precise and evaluable measurements with relatively little effort. With the help of the Meldesches tube, the students can easily be introduced to scientific methods (measurement evaluations, determining functional relationships, etc.).
Individual evidence
- ↑ Carl Fischer: The Melde's capillary barometer . Universitäts-buchdruckerei (R. Friedrich), 1889 ( limited preview in Google book search).
- ↑ F. Heywang, E. Nücke, J. Timm, W. Timm: Physics for Technicians Hamburg 1984231.
- ↑ EXPANSION ON WARMING, GAS LAWS
- ↑ Physical student experiments card index 2000, Dr. H. Kröncke OHG, Hanover, June 1, 1968.