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Properties of cathode rays

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To determine some of the properties of the rays which come from the cathode of a discharge tube.


  • two power packs
  • two plug-plug leads
  • one pair of magnets
  • induction coil
  • four plug-clip leads
  • discharge tubes (maltese cross, electric plates, rotating wheel, screen display)


  1. Connect the power pack to the induction coil and set it at 6 volts. Adjust the points on the induction coil so that a strong steady spark is being produced.
  2. Connect the terminals of the induction coil to the discharge tube containing the maltese cross (Crooke’s tube). Observe the end of the tube containing the cross when the cross is down and when it is up.
  3. Replace the Crookes’ tube with the tube containing the electric plates and connect the terminals of the plate to its high DC voltage supply.
...read more.


  • In Crookes’ tube, the upright cross produced a shadow in the green glow on the end of the tube opposite the cathode, showing the path of the beam was blocked by the metal cross. It was observed from this that cathode rays travel in straight lines.
  • Using the tube with the metal plates, these plates were positively charged and so the beam would flow from the cathode and into the plates and it was concluded that these cathode rays were negatively charged.
  • As the cathode rays were projected on to the fluorescent screen, I could see that the rays were in a straight line on the screen, by bring magnets next the tube it could be seen that this beam is deflected by magnetic fields.
  • Finally the tube with the paddle wheel is connected, the paddle wheel is originally at the cathode. When the power is switched on the paddle wheel rolls from the anode to the cathode, from this I observed that these cathode rays had momentum.
...read more.


though an electric field. It was observed that the cathode ray was attracted to the positive plate. This suggested that cathode rays were negatively charged particles as waves cannot be charged.



In this experiment cathode rays were shone though a phosphorus screen. This allowed for their path to be observed. It was noticed that the path of the cathode rays was affected by a magnetic field, such as when magnets were placed near it.



In this experiment cathode rays were shone onto a glass wheel that was free to move. It was observed that the glass wheel moved. Meaning that the cathode rays must have mass (in order to have the momentum to make the wheel move), this meant that cathode rays must be particles as waves cannot have mass.


...read more.

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