Measuring instruments — match each instrument in List I with its correct classification/use in List II. List I (Instrument) A. Tangent galvanometer B. Moving-coil instrument (PMMC) C. Household energy meter D. Electrostatic instrument List II (Classification / Use) 1. Can be used for DC only 2. Integrating instrument (measures energy over time) 3. Used for voltage measurement only (high-voltage capable) 4. Absolute instrument (primary standard)

Introduction / Context:
Instrument classification clarifies what quantity an instrument measures and whether it serves as a primary standard or a secondary indicating device. Correct mapping is vital for calibration labs, power metering, and electrical measurements courses.

Given Data / Assumptions:

• Tangent galvanometer uses the tangent law to relate current to deflection in Earth’s magnetic field.
• PMMC (permanent-magnet moving-coil) instruments are inherently DC devices unless rectified for AC.
• An energy meter integrates power over time to register watt-hours or kilowatt-hours.
• Electrostatic instruments respond to electric field energy and are suited to voltage measurement, even at high voltage.

Concept / Approach:

Identify whether each instrument is absolute (primary standard), DC-only, integrating, or voltage-only. The tangent galvanometer is an absolute instrument because current can be determined from geometry and field constants. PMMC is accurate for DC. Energy meters are integrating instruments by design. Electrostatic instruments measure force proportional to V^2, ideal for high-voltage measurement and essentially limited to voltage.

Step-by-Step Solution:

Verification / Alternative check:

Textbook classifications: PMMC needs rectifiers for AC; induction-type meters integrate power over time; electrostatic voltmeters measure potential difference with negligible current draw; tangent galvanometer can be used to derive absolute current based on known Earth's field and coil geometry.

Why Other Options Are Wrong:

• Assigning PMMC to AC would ignore its magnetic flux dependency and rectification need.
• Labeling the energy meter otherwise than integrating contradicts its function.
• Electrostatic instruments are not general-purpose ammeters or power meters.

Common Pitfalls:

Confusing “absolute” with “precision.” Absolute refers to principle of operation not requiring prior calibration against another meter (within limits), unlike many secondary instruments.

Final Answer:

A-4, B-1, C-2, D-3