C5 Electronics

    Cards (6)

    • Thermionic emission is the emission of free electrons from a hot cathode.
    • Cathode Ray: high velocity electron beam produced using thermionic emission in a vacuum tube.
    • Production of cathode ray:
      • cathode is heated by passing current until it gets hot
      • hot cathode emits free electron through thermionic emission
      • free electrons accelerates with a high velocity towards positively charged anode in vacuum tube
      • beam of high velocity electrons known as cathode rays
      • cathode rays complete the EHT circuit and milliammeter reading shows current on EHT circuit
    • Characteristics of cathode ray:
      • travel in straight line in vacuum tube
      • have momentum
      • have kinetic energy
      • negatively charged
      • produces fluorescence when hit phosphor
      • can be stopped by Maltese Cross
      • can be deflected by electric and magnetic field
    • Deflection of cathode rays
      • not deflected in absence of electric field - travels straight line
      • has electric field - deflects toward positively charged plate in a parabolic path
    • Effects of magnetic field on the direction of the cathode rays with a Maltese Cross:
      • with torchlight - opaque Maltese Cross blocks light passing in a straight line
      • electron gun with both switches on - shadow of Maltese Cross forms when cathode rays are blocked - fluorescent effect on cathode rays due to momentum and kinetic energy
      • North pole placed near cathode ray - Maltese Cross deflects downwards following Fleming LHR - cathode rays are deflected by magnetic field