Measurement basics: Is a galvanometer primarily a device for measuring very small voltages? Differentiate between galvanometers, ammeters, and voltmeters in terms of the quantity they sense directly.

Introduction / Context:
Analog meters share similar moving-coil mechanisms but differ in how they are configured to measure current or voltage. This question clarifies that a galvanometer is fundamentally a sensitive current-measuring device, not a voltage meter per se.

Given Data / Assumptions:

• Classic D’Arsonval (PMMC) galvanometer mechanism is assumed.
• “Very small” refers to microampere-level sensitivity.
• No external multipliers or shunts unless explicitly added.

Concept / Approach:

A bare galvanometer measures current through its coil by magnetic torque proportional to coil current. To measure voltage, a high-value series resistor (multiplier) is added, creating a voltmeter whose input current remains within the galvanometer’s safe microampere range. Conversely, to measure larger currents, a shunt resistor is used to bypass most current, turning the system into an ammeter.

Step-by-Step Solution:

Verification / Alternative check:

Instrument datasheets specify movement sensitivity in microamperes per full-scale deflection (e.g., 50 μA FSD), confirming current as the primary measurand. Voltage ranges are derived from added series resistance.

Why Other Options Are Wrong:

• “True” misidentifies the primary quantity.
• “Only if a series multiplier is used” describes a voltmeter made from a galvanometer, but the original statement claims the galvanometer itself measures voltage.
• AC microvolt claims are inappropriate for PMMC movements without rectification; galvanometers are DC devices.

Common Pitfalls:

Equating the presence of voltage terminals on a commercial meter with the internal sensing principle. The core mechanism always responds to current.

Final Answer:

False