Crookes tube

This is an in depth review of the Crookes discharge tube.

4 Experiments with Crookes tubes
4.1 Maltese cross
4.2 Perpendicular emission
4.3 Deflection by electric fields
4.4 Deflection by magnetic fields
4.5 Paddlewheel
4.6 Charge
4.7 Canal rays
4.8 Doppler shift
4.9 Lenard window

Let me make it perfectly clear, the Jacaranda text book has so many errors in it, it is very clear the people writing it have not performed experiments or done even basic research.

Crooke built a basic vacuum tube with two electrodes. The word tube refers to glass bulb that is is connected to a vacuum pump. It is pumped out and put in an oven. The heat means any dirt is turned in to vapour and is pumped out. When the desired pressure is reached the glass tube connected to the vacuum pump is heated, atmosperic pressure closses the soft tube and it forms a sealed vacuum chamber.

This the closest image to heat sealing a tube

The syllabus say the pressure is 10-4 atm. I can tell you from making these devices the pressure is 10-7 atm and this the figure quoted in Wikapeadia

You can see clearly that the rays are emerging from a point in the centre of flat plate. The text book says this was taken as evidence of the wave rays emerging from the metal like a sound wave. However Wikipeadia states the if it was thought to be waves like light it would radiate like light in all directions light a electric light filament. Instead the particles followed the field lines. So they leave radially from a sphere, and straight out of a flat plate.

Why do the electrons leave from a single pit in the center of the flat electrode? The student who decided to sit at the back of the class and not look because it was boring is locked into a do loop.

I can answer this from my experiance working with Laser electrodes. Positive ions will pit the electrodes and this local curvature will create a local high field. If you want the entire electode to emit it has to be heated. This is exactly what you see in the demostration Cathode ray tube. When the metal heats up, it emits a uniform flow of electrons, but as before perpendicular from the surface. If you want an analogy the electrons flying the electric field are like rain falling down.

The emission of electrons from a hot metal is called "Thermionic" emission.

The fact that the shadow has crisp edges and is larger than the maltese cross shows also that the source of light is from a single point.

The process of glass or crystals glowing is called flouresence. The phosphor has a crystal stucture. When it is hit by an electron it emits light rather than heat. Glass and other disordered substance trap electrons in the random voids of the structure. There are not a large number of configurations of the matterial to rattle down and convert to heat, so the electrons inside the matterial change shape in a single leap emitting light. The process of the electrons moving in the voids of the glass shifts the voids creating path ways for the electrons to rattle down without creating light.

The blue glow in the Crookes space is from positive atom ions that recombine.

Why don't the electrons make a bee line to the positive electrode? They would if the vacuum tube was at really high vacuum the small amount of gas, become positively charged making it really a positive electrode just milimeters from the surface of the negative electrode.