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Semiconductor Electronic: Material, Devices And Simple Circuits — Physics STD 12 Science — Question

Gujarat BoardEnglish MediumSTD 12 SciencePhysicsSemiconductor Electronic: Material, Devices And Simple Circuits1 Mark
MCQ
Two statements are given $-$ one labelled Assertion $(A)$ and the other labelled Reason $(R)$. Select the correct answer to these questions from thecodes $(a), (b), (c)$ and $(d)$ as given below.
Assertion: Light Emitting Diode $(\text{LED})$ emit spontaneous radiation.
Reason: $\text{LED}$ are forward $-$ biased $p - n$ junction.
  • A
    Both $A$ and $R$ are true and $R$ is the correct explanation of $A$.
     
  • ✓
    Both $A$ and $R$ are true but $R$ is not the correct explanation of $A$.
     
  • C
    $A$ is true but $R$ is false.
     
  • D
    $A$ is false and $R$ is also false.
✓

Answer

Correct option: B.
Both $A$ and $R$ are true but $R$ is not the correct explanation of $A$.
 
In semiconductor there may be energy bands due to donor impurities $(E_D)$ near the conduction band or acceptor impurities $(E_A)$ near the valence band.
When electron falls from higher to lower energy level containing holes, the energy is released in the form of radiation.
The energy of radiation emitted by $\text{LED}$ is equal or less than the band gap of the semiconductor used.
The radiation released lies in range of visible light whose colour depends on the semiconductor used.

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