JFET carrier flow directions: In a junction field-effect transistor, do charge carriers move from source to drain in a p-channel device and from drain to source in an n-channel device?

Difficulty: Easy

Correct Answer: Incorrect

Explanation:


Introduction / Context:
Understanding current and carrier flow directions in junction field-effect transistors (JFETs) is foundational in electronics. The statement mixes up conventional current with actual charge-carrier motion for p-channel and n-channel JFETs. Clarifying this distinction helps prevent sign and polarity mistakes when biasing or analyzing JFET circuits.


Given Data / Assumptions:

  • N-channel JFET uses electrons as majority carriers; p-channel JFET uses holes.
  • Standard terminal naming: gate (G), drain (D), source (S).
  • Biasing is such that the gate-channel junctions remain reverse-biased in normal operation.
  • Conventional current direction is defined as positive charge flow.


Concept / Approach:
In an n-channel JFET, conventional drain current (ID) flows from drain to source, but electrons (negative carriers) physically move from source to drain—opposite to conventional current. In a p-channel JFET, holes are the carriers and move from source to drain; conventional current also flows from source to drain. The statement claims carriers move source→drain in p-channel (true) and drain→source in n-channel (false; electrons move source→drain).


Step-by-Step Solution:

Identify the device: n-channel or p-channel.Recall carrier type: electrons (n-channel), holes (p-channel).Relate carrier motion to conventional current: carrier motion is opposite to conventional current for electrons and the same for holes.Evaluate claim: p-channel portion is consistent; n-channel portion is not—hence the overall statement is incorrect.


Verification / Alternative check:
Use the sign of VDS and the established symbol conventions: for an n-channel device, typical operation has the drain at a higher potential than the source. Electrons flow toward the drain terminal internally from the source side, confirming source→drain carrier motion for electrons.


Why Other Options Are Wrong:

Depends only on VDS: channel type and carrier charge determine direction, not VDS alone.Correct: contradicts n-channel carrier motion.Undefined: carriers absolutely move in the channel under bias.Always drain→source: true only for conventional current in n-channel, not for carrier motion.


Common Pitfalls:
Confusing conventional current with electron flow; assuming both channel types share the same carrier direction; forgetting that diagrams typically show current arrows, not carrier drift direction.


Final Answer:
Incorrect

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