Explain that cathode ray tubes allowed the manipulation of a stream of charged particles
  • A Cathode Ray Tube (or a Discharge Tube) is an evacuated glass tube with electrodes at the ends of the tube.
  • Geissler and Plucker discovered that an evacuated tube could conduct electricity with a high potential difference in this method in 1855.
  • They also found that, the glass at the positive end (anode) glowed a green colour.
  • This discovery led to investigations on these tubes and what they were capable of.
  • Eugene Goldstein determined that the "ray" came from the negative end(Cathode), and coined the name.
  • Through various experiments (described here and here), it was shown that this ray was actually a stream of electrons.
  • What happened was that:
    • As a high Voltage is inputted, a filament in the cathode gets heated up and this excess of energy is enough to set the electrons free. (thermionic emission)
    • The free electrons are then attracted to the positive anode on the other end of the tube.
    • This stream of electrons flowing is the cathode ray.
  • These electrons can be manipulated with electric and magnetic fields as they are (obviously) electrically negatively charged.