Magdeburg Hemispheres 1003208

® 3B SCIENTIFIC PHYSICS

Instruction Sheet 05/18 ALF

1 Hose nipple 2 Stopcock or ventilation valve 3 Hemisphere 4 Handle

1. Safety instructions 3. Technical data  Do not try to pry the two evacuated Vacuum connection: 8 mm hemispheres apart using tools. Diameter: 120 mm  Do not try to separate the hemispheres using Hose length: 110 mm ropes or similar, because when they do

separate they can turn into projectiles.

 When ventilating the hemispheres hold on tight to the apparatus so that you can avoid 4. Operating principle any damage from the hemispheres falling. A protective mantle of air called the atmosphere  Ample space should be left behind the surrounds the earth. The air molecules like all persons trying to separate the Magdeburg other materials are subject to the force of gravity plates. and thus become concentrated at the earth’s surface. The atmospheric pressure, which is exerted by the air mass, is highest at sea level and gradually decreases with increasing distance 2. Description from the earth’s surface. Air pressure like any The Magdeburg hemispheres are used to liquid exerts equal and constant pressure on all demonstrate the effect of atmospheric pressure sides of an object. In an open object equilibrium (historical experiment according to Otto von always prevails between internal and external Guericke). pressure. If the internal pressure drops more than the external pressure, the state of equilibrium is Two plastic hemispheres with handles and inlaid reestablished by letting air in. Conversely, if the rubber sealing rings can be joined vacuum tight. internal pressure becomes greater than the One hemisphere is equipped with stopcock or prevailing external pressure, there is the same ventilating valve and hose connection. A short tendency to escape. In an enclosed object the hose completes the apparatus. force resulting from the difference between the internal and external pressures affects the object’s surface either causing it to compress or in the latter case causing the object to explode.

1 The physicist and mayor of Magdeburg Otto von  Before starting the experiment check ensure Guericke was the first to demonstrate the effect of that the rubber seal ring is correctly situated atmospheric pressure. His vacuum experiments and that it is undamaged. commenced around 1650 and reached their  Connect the hemisphere with stopcock to a zenith in 1654 in a spectacular experiment pump and open the valve. attended by Kaiser Ferdinand III in the town of  Place the second hemisphere on the first one Regensburg: the famous Magdeburg and press the two of together. hemispheres. To do this von Guericke evacuated the air out of two copper hemispheres of 42 cm  A second person starts the evacuation diameter and sealed with an oil and wax process. saturated leather lining. The air pressed the  After a short time (depending on the pump’s hemispheres together with such force that even pumping power) stop the pump, close the 16 horses were unable to pull them apart. stopcock and loosen the hose connection.  Demonstrate the effect of atmospheric pressure by trying to pull the hemispheres 5. Operation apart.  After completing the experiment ventilate the Additionally required: sphere by opening the valve. Make sure you 1 Vacuum pump e.g. hold on to the hemispheres to avoid any Vacuum hand-operated pump 1012856 damage from them falling down.