Which electromechanical device is best described as a coil that produces linear motion of a movable iron plunger or core when energized?

Introduction / Context:
Coils can convert electrical energy into mechanical motion in several ways. Identifying the correct device by its construction and motion is important for applications such as valves, latches, and actuators.

Given Data / Assumptions:

• The device has a wound coil.
• It contains a movable iron core or plunger.
• When energized, it produces a linear push–pull motion.

Concept / Approach:
A solenoid consists of a coil and a ferromagnetic plunger that is drawn into the coil when current flows, producing linear motion. Relays also use coils but operate contacts via a pivoted armature; reed switches are magnetically actuated contacts sealed in glass and lack a moving iron plunger as described. An “armature” is a component inside machines and relays, not a complete device. Voice coil actuators are similar in function but are built differently and usually do not use an iron plunger; they employ a coil in a magnetic gap for precise motion.

Step-by-Step Solution:
Match description: coil + movable iron core = solenoid.Exclude relay: coil actuates contacts via lever/armature, not a plunging core as the main motion.Exclude reed switch: no iron plunger; uses magnetic fields to close reed contacts.Exclude armature: that is a component, not the full device.

Verification / Alternative check:
Component catalogs list solenoids specifically for linear actuation with plunger strokes and force ratings, confirming the definition.

Why Other Options Are Wrong:
Reed switch: passive magnetically actuated contacts; no plunger motion.

Relay: primarily an electrical switch; movement is of an armature, not a sliding iron core inside the coil as the actuator itself.

Armature: not the complete device.

Voice coil actuator: typically lacks an iron plunger and uses different geometry.

Common Pitfalls:
Calling any coil-driven motion a relay. Relays switch contacts; solenoids create linear force and displacement.

Final Answer:
solenoid