Maltese Cross Electron Tube

maltese1maltese2maltese3maltese4

 

 

 

 

 

Equipment: 

  • Maltese cross electron tube
  • Electron tube stand
  • 5000V DC Power Supply with 6.3V AC (shown in picture)
  • Bar magnet
  • banana cables ( 2 red, 2 black)

Demo:

  1. Place the electron tube securely on the stand
  2. Follow the diagram above to hook up the tube to the power supply properly.
  3. Turn on 6.3V AC first to heat the cathode of electron gun, then slowly increase HV to 4000V
  4. Use the bar magnet to distort the shadow cast on the the screen
  5. Before turning off the apparatus, reduce HV to zero (otherwise the cathode can be damaged)

Explanation:

This demonstration emphasizes the particle properties of electrons. A metal cross inside of an electron tube blocks off an electron beam, forming a dark shade on the fluorescent screen. The screen produces a green glow when the electrons collide with it. If you increase the voltage, the electrons will gain more energy and move faster when they hit the screen. This makes the glow much brighter. The increased brightness is also because the electron gun is producing more electrons. If you touch the front of the screen the image will move because you are grounding it, and the electrons collected on the screen will flow through you to the ground. Using a bar magnet, the instructor can show electron beam deflection by distorting the shadow cast on the screen.Holding a magnet near the tube will distort the picture, showing that electron beams are affected by magnetic fields.The shadow moves the same way according to the magnetic field, which shows that all particles in the stream are being deflected by the same amount. This means they have the same ratio of charge to mass. Electrons are also likely to have the same charge and same mass (though, from this experiment alone we cannot be sure).

Written by Nick McCabe