Glow discharge tube

When you start the experiment, a vacuum is formed in the tube and an electrical charge is placed across the ends of it. The ends are known as the “anode” (+) and the “cathode” (-). Charged particles that collect at each end of the tube start to emit light: positive charges gather at the cathode and negative charges at the anode.

When the electrons collide with gas molecules in the tube they gain some energy. When they subsequently relax to their normal energy state, they emit light. The electrons that collide with contaminants in the glass emit a blue colour.

A magnet is hanging beside the tube. Move it close to the glass tube. You see that the pathways of the charges can be bent by a magnetic field.