Cathode Rays

• What is a cathode?

  A negatively charged electrode
• What is an anode?

  A positively charged electrode
• What are the components of a discharge tube?

  • Glass chamber
  • Low pressure gas
  • Anode at one end
  • Cathode at the other
  • Connected to a high voltage supply
• What happens when a potential difference is applied in a discharge tube?

  The gas glows due to cathode rays

  
• What are cathode rays hypothesized to be caused by?

  Emissions from the cathode
• What do cathode rays consist of?

  Negatively charged particles
• How does the discharge tube conduct electricity?

  • Electric field ionizes gas particles
  • Forms positive ions and electrons
  • Electrons move to the anode
  • Positive ions move to the cathode
• Why can charged particles travel in a discharge tube?

  The gas pressure is low enough
• What happens to electrons emitted from the cathode?

  They travel towards the anode
• Why does the gas glow in a discharge tube?

  • Electrons and positive ions travel in opposite directions
  • They gain energy due to low pressure
  • Collisions lead to recombination in an excited state
  • Electrons de-excite, emitting visible photons

  
• Why must the gas be at low pressure to emit light?

  • Particles are widely spaced
  • Fewer obstacles for charged particles
  • Allows for high-energy collisions
  • Enables excitation of atoms
• What is the effect of a high potential difference in a discharge tube?

  It causes the cathode to emit electrons
• What is the result of positive ions and electrons colliding at high speed?

  They recombine, emitting photons
• What is the first step in explaining how gas conducts in a discharge tube?

  Recall the need for charged particles
• How does the electric field affect the movement of charged particles?

  It accelerates electrons and positive ions
• What is the significance of the distribution of particles in low pressure gas?

  It allows easier excitation of atoms
• Why do fewer obstacles in low pressure gas matter?

  They allow for high-energy collisions