Class 12 Physics Semiconductor Electronics Introduction


We know that earlier electronic devices were made up of vacuum tubes or valves

Vacuum tubes or Valves:

  • The evolution of vacuum tubes started with diode and proceeded to triode, tetrode and pentode
  • Valves control the flow of electrons; In diodes, there were two electrodes – cathode and anode
  • Similarly, triode had three electrodes – cathode, grid and anode; tetrode had four electrodes – anode, two grids and cathode; pentode had five electrodes –anode, three grids and cathode
  • Generally in vacuum tubes, the electrons are produced by heating the cathode using low tension battery; The vacuum helps in electron not losing its energy by collision with air molecules in the way
  • However, the vacuum tube devices had some disadvantages and they are
    • Bulky
    • Operate at high voltages
    • Consume more power
    • Have limited life
    • Low reliability

  Diodes and transistors

  • Next came the discovery of semiconductor junction, namely, junction diode and transistors
  • These replaced the vacuum tubes or valves

  • The advantages of semiconductor devices are
    • Small in size
    • Operate at low voltages
    • Consume small power
    • Long life
    • High reliability
  • Though the above advantages are present, the circuits consisting of transistors were still bulky, less shock proof
  • Hence, it led to the discovery of integrated circuits which is a major revolution in the electronic industry

Example – The earlier generation television and computer monitors were very bulky as they were based on the principle of vacuum tubes; now days, we have LCD (Liquid Crystal Display) monitors which support solid state electronics

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