A teltron tube (named for Teltron Inc., which is now owned by 3B Scientific Ltd.) is a type of cathode ray tube used to demonstrate the properties of electrons. It usually contains two electron guns, which can project two thin electron beams at right angles. The beams can be bent by applying voltages to various electrodes in the tube. The electron beams are visible as fine bluish lines. This is accomplished by filling the tube with low pressure helium gas. A few of the electrons in the beam collide with the helium atoms, causing them to fluoresce and emit light.
They are usually used to teach electromagnetic effects because they show how an electron beam is affected by electric fields and by magnetic fields.
Charged particles in a uniform electric field follow a parabolic trajectory, since the electric field term (of the Lorentz force which acts on the particle) is the product of the particle's charge and the magnitude of the electric field, (oriented in the direction of the electric field). In a uniform magnetic field however, charged particles follow a circular trajectory due to the cross product in the magnetic field term of the Lorentz force. (That is, the force from the magnetic field acts on the particle in a direction perpendicular to the particle's direction of motion. See: Lorentz force for more details.)
The 'teltron' apparatus consists of a Teltron type electron deflection tube, a Teltron stand, EHT power supply (0 - 5000 V DC, variable).