Analog Electronics
The extremely high input impedance of a MOSFET is primarily due to the

  extremely small leakage electric current of its gate capacitor.
  absence of its channel.
  negative gate-source voltage.
  depletion of electric current carriers.

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Analog Electronics
Optocouplers combine

  Infrared light emitting diode and a silicon photo transistor.
 SITs and BJTs.
 IGBTs and MOSFETs.
 Power transistor and silicon transistor.

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Analog Electronics
Pinch-off voltage in a JFET is

 the drain voltage that gives zero drain current.
 the gate to source voltage that gives zero drain current.
 the drain voltage that gives infinite drain current.
 the gate to source voltage that gives unity drain current.

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