Physics Notes

Physics 9.3 - From Ideas to Implementation

1. Increased understandings of cathode rays led to the development of television.

1. Explain that cathode ray tubes allowed the manipulation of a stream of charged particles.

A cathode ray tube is a glass tube with an electrode attached to each end, and by use of a vacuum pump, most of the air evacuated to create a low atmosphere system. When a high voltage is passed through the electrodes, a current is produced and mysterious pale green lights are seen on the glass – thus we know ‘cathode rays’ are passing from the cathode to the anode.
Light caused by cathode rays striking air particle in the tube that becomes excited and releases a photon of visible light, which forms in strips or striations depending on the pressure. The gas type changes the colour of the striations.

A cathode ray tube allows the manipulation of the cathode ray because:
The pressure and voltage can be varied, and objects can be placed around the tube (electric and magnetic plates) or inside (Maltese cross, paddle wheel.)
In everyday life, cathode ray tubes are used in neon signs. A small amount of gas is in the tube, which, when excited by a high potential, glows with a certain colour (neon = red)

PRAC 1: Perform an investigation and gather first-hand information to observe the occurrence of different striation patterns for different pressures in discharge tubes.

• A set of glass discharge tubes at different pressures are arranged on a board
• Each tube contains an electrode at each end to allow the application of a large voltage, provided by the induction coil. High voltage causes an electrical discharge through the air in the tube, causing the air to glow.
• Different discharge patterns are formed at different pressures
• Under normal conditions of temperature and pressure, air is an insulator, but at reduced pressure, air and all other gases conduct electricity.

• At 5% atmospheric pressure,...