Electromechanical meter movement identification: Which electromagnetic device consists of a light coil that rotates in a permanent magnetic field on jeweled bearings to indicate current or voltage?

Introduction / Context:
Analog panel meters and galvanometers use precise electromagnetic mechanisms to display current and voltage. Recognizing the specific movement type helps with calibration knowledge, scaling, and interpreting meter response characteristics such as sensitivity and damping.

Given Data / Assumptions:

• Device has a coil that can rotate in a permanent magnetic field.
• It uses jeweled bearings for low friction and high sensitivity.
• Used for indicating electrical quantities on a scale.

Concept / Approach:
The classic moving-coil meter is the d’Arsonval (or Weston) movement. Current in the coil generates torque in the magnetic field, causing rotation proportional to the measured current (or proportional to voltage via series resistance). The core features—moving coil, permanent magnet, jeweled bearings—clearly identify this movement.

Step-by-Step Solution:

Verification / Alternative check:
Any analog multimeter teardown or galvanometer description confirms the moving-coil d’Arsonval structure with jeweled pivots and restoring springs.

Why Other Options Are Wrong:

• Permanent-magnet speaker: Uses a voice coil and cone to produce sound, not a metering mechanism.
• SPDT relay: An electromechanical switch, not a precision indicating movement.
• Crankshaft position sensor: Typically magnetic/inductive or Hall-effect, not a jeweled moving coil.

Common Pitfalls:
Confusing any “coil + magnet” device with a meter movement; the jeweled pivot and calibrated pointer are key identifiers.

Final Answer:
d’Arsonval movement