Production of cathode rays

Cathode rays are streams of electrons produced in a discharge tube containing gas at very low pressure. The tube has two electrodes: a negative cathode and a positive anode. A high potential difference between them creates an electric field.

Electrons released from the cathode are accelerated by the electric field towards the anode. The low gas pressure means there are few gas particles in their path, so the electrons undergo fewer collisions and can travel through the tube.

Some electrons collide with the remaining gas particles and ionise them, producing positive ions. The electric field drives these positive ions towards the cathode. When they strike it, they can release further electrons, helping to sustain the discharge.

If the anode has a suitably positioned opening, some electrons pass through it and continue beyond the anode as a cathode-ray beam.