A PN junction diode that ____ when activated is called a/an _______.

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RRB ALP Electronics Mechanic 23 Jan 2019 Official Paper (Shift 2)
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  1. emits photons; LCD
  2. emits electrons; diode
  3. emits electrons; regulator
  4. emits light; LED

Answer (Detailed Solution Below)

Option 4 : emits light; LED
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The correct answer is option 4.

Light Emitting Diode (LED)

  • It is a PN junction diode that emits light when it is forward-biased.
  • When forward current is passed through the light-emitting diode, carriers (electrons and holes) move.
  • The holes in the p-type region move to the n-type region and the electrons in the n-type region move to the p-type region.
  • The injected carriers recombine, and the energy difference before and after recombination is released as light. 
  • The color of the light is determined by the energy required for electrons to cross the band gap of the semiconductor.
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