Properties of cathode rays

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AIM

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

APPARATUS

  • 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)

METHOD

  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. Observe the effects of the electric field on the cathode rays.
  4. Connect the tube with the fluorescent screen display to the induction coil and record the effect of placing a set of bar magnets around the cathode rays.
  5. Finally, attach the tube containing the paddle wheel on tracks to the induction coil and observe the effects that the cathode rays have on the wheel when the tube is horizontal.
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RESULTS

  • 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 ...

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