Electricity & Magnetism

Glow Discharge Tube

GLOW DISCHARGE TUBE demonstrates electrical effects in a low-pressure gas. The visitor can vary the voltage and air pressure in a large cylindrical tube. If gas is leaked into the tube up to atmospheric (or almost atmospheric) pressure, all glowing ceases. As the vacuum pump reduces the pressure in the tube, it begins to glow pinkish-orange. As the pressure further decreases, the glow breaks up into light and dark spaces (Crooke's dark spaces). After this phenomenon, the orange glow disappears completely, leaving behind a blue violet glow which slowly gets dimmer until the tube is once again dark, except this time at a low pressure. A magnet hangs from the exhibit which allows the visitor to demonstrate that moving charges can be deflected by a magnetic field. Meters are provided which give an indication of the current flowing in the tube as well as the gas pressure.