The metal filament heats up and its electrons escape in the form of thermionic emission. Now can you see a spot?Ī spot is only visible on the fluorescent screen when the cathode is connected. Reconnect the voltage lead to the cathode and repeat the previous step.Can you see a spot on the fluorescent screen? Connect the power unit to a source of electricity.Set the voltage of the anode to 30–50 V.Set the voltage of the auxiliary anode – the anode of the control grid or Wehnelt cylinder – to 10 V.On the CRT power supply unit, disconnect the lead that supplies the voltage to the cathode (see the circuit diagram in the attached worksheet).See the list of the necessary materials in the downloadable document w1 Procedure For all activities, the particle accelerator needs to be set up as outlined in the worksheet that can be downloaded w1. All four activities could occupy a class for at least half a day, but they could also be used separately in individual lessons. The activities described below enable students to control the same parameters in a CRT as scientists do at the LHC: creating a particle beam, changing the path of the particles and altering their speed. To collide the beam of particles with a second beam and observe the result To cause a beam of particles to form an image on a fluorescent screen Strong magnetic fields achieved using superconducting electromagnets (4 T in strength) Protons produced by ionisation of hydrogen atomsĪ potential difference between the anode and cathodeĮlectronic fields and radio frequencies, synchronised with particle speed.Pressure (For comparison, a vacuum cleaner has a pressure of 1‒10 -3 atm, and outer space has a pressure of <10 -15atm)ĭistance travelled by a particle between collisionsĮlectrons produced by thermionic emission at the cathode (a heated filament) Photo courtesy of CERN Table 1: A comparison of the classroom particle accelerator (the CRT) and CERN’s LHC Characteristic The image could be, for example, electrical waveforms (on an oscilloscope), radio wave echoes of aircraft or ships (on a radar screen) or pictures on an old-fashioned television screen or computer monitor
The electrons can then be deflected by a magnetic (or in the case of oscilloscopes, an electrical) field (D) before they strike the phosphorescent screen (E), creating an image. Starke observed the differences in the mechanical reaction for strong and weak electrical currents, changes in vacuum pressure, metallic and non-metallic surface materials, and different angles of incidence of the beta rays on the surface, and concluded that thermal effects were greater than the mechanical impulse imparted by the electrons.Figure 1: The cathode ray tube is a vacuum tube in which electrons are produced by a heated filament (the cathode, A), focused into a beam as they pass through the aperture of the control grid (Wehnelt cylinder, B) and accelerated by the voltage (VA) between the cathode and the anode (C). Starke "Notiz über die mechanische Wirkung der Kathodenstrahlen" Annalen der Physik 3, (1900) pages 101-107. Thomson "Conduction of Electricity Through Gases" Cambridge University Press 1903 p.501ģH.
The tube is only about 12" long and the paddle wheel a few centimeters in diameter, so video projection should be used when presenting to a large audience.ġSir William Crookes "On Radiant Matter" Popular Science Monthly, London 1880 p.158ĢJ. Great care must be taken to make sure the tube is level and the frictional forces on the axle of the paddle wheel can be overcome. Use the same 6V battery and induction coil used for the Maltese Cross and Cathode Ray Deflection Crookes tubes. Please use gloves and safety glasses when handling this fragile vacuum tube. Starke, showed that momentum transfer of the electrons was not enough to account for the observed motion of the paddle wheel, and concluded that the kinetic energy of the electrons only indirectly leads to movement of the paddle wheel via radiometric effect.
Thomson, citing the experimental work of H. In 1880 Sir William Crookes argued that the mechanical impulse of the electrons hitting the vanes caused the observed motion-similar to how flowing water turns the arms of a turbine. Flourescent material on the vanes glow green when subjected to the energetic electrons. When 40kV is applied across the tube, the lower vanes directly between the cathode and anode pivot away from the cathode, causing the wheel to move.
#CATHODE RAY TUBE EXPERIMENT IN HIGH SCHOOL FREE#
A beam of cathode rays (electrons) impinging on a paddle wheel cause it to spin and travel down the vacuum tube.Ī paddle wheel is suspended by its axle inside a Crookes tube so that when the paddle vanes spin the entire wheel is free to travel the length of the tube.
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