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When a voltage is applied across a semiconductor crystal, in which direction do the free electrons move?

Difficulty: Easy

Correct Answer: towards positive terminal

Explanation:


Introduction / Context:
Direction of carrier flow in semiconductors is a fundamental concept that underlies all device physics, from diodes to transistors. The drift motion of electrons and holes under an applied electric field determines current direction and polarity.


Given Data / Assumptions:

  • Electrons carry negative charge.
  • Voltage is applied across a semiconductor crystal.
  • Conventional current is defined in the direction of positive charge flow.


Concept / Approach:
Electrons, being negatively charged, are attracted to the positive terminal of the applied voltage. Holes (if considered) move toward the negative terminal. This bidirectional movement results in a net current consistent with conventional direction.


Step-by-Step Solution:

Apply an electric field across the semiconductor.Electrons experience force opposite the field, i.e., drift toward the positive terminal.Therefore, free electron motion is toward the positive terminal.


Verification / Alternative check:

For copper wires: electron flow is toward the positive battery terminal. The same holds in semiconductors.


Why Other Options Are Wrong:

Negative terminal: would be true for holes, not electrons.Alternating 1 μs reversal: irrelevant and incorrect.Random: only true with no field.


Common Pitfalls:

Confusing conventional current with electron current.


Final Answer:

towards positive terminal
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