Difficulty: Easy
Correct Answer: A speaker
Explanation:
Introduction / Context:
Loudspeakers convert electrical audio signals into acoustic pressure waves. The classic electrodynamic speaker uses a flexible cone (diaphragm) that moves air in response to current through a voice coil situated in a static magnetic field.
Given Data / Assumptions:
Concept / Approach:
An audio signal through the voice coil produces a force F = B * I * L that moves the coil. The coil is attached to a cone suspended by a surround and spider, allowing axial motion. As the cone vibrates, it compresses and rarefies air, producing sound corresponding to the input waveform. None of the other listed devices use a flexible cone in their operation.
Step-by-Step Solution:
Identify unique mechanical part: flexible cone.Associate with device: electrodynamic loudspeaker.Exclude alternatives: DC generator (commutator and brushes), relay (contacts and armature), solenoid (plunger).Select: “A speaker.”
Verification / Alternative check:
Exploded diagrams of speakers show cone, dust cap, voice coil former, spider, surround, and permanent magnet assembly.
Why Other Options Are Wrong:
DC generator: rotating armature and commutator, no cone.Relay: switches contacts; no diaphragm for acoustic output.Solenoid: linear actuator; no flexible acoustic radiator.
Common Pitfalls:
Confusing “speaker” with “microphone”; although related by transduction, microphones usually do not use large flexible cones except in some dynamic designs, and their purpose is opposite (sound to electricity).
Final Answer:
A speaker
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