A moving iron type ammeter has few turns of thick wire so that

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Resistance is less

Explanation: A moving iron ammeter is connected in series with the load to measure current, meaning it must have negligible internal resistance to avoid affecting the circuit current. By using a few turns of thick wire, the meter achieves a low resistance while maintaining sufficient Ampere-turns to produce the required deflecting torque.

Working Principle: The deflecting torque in a moving iron instrument is given by $T_d = \frac{1}{2} I^2 \frac{dL}{d	heta}$. To measure current without altering the circuit conditions, the instrument must act as a near-perfect short circuit. Thick wire reduces the DC resistance $R = ho \frac{l}{A}$, where area $A$ is large, keeping power dissipation $I^2R$ minimal and preventing excessive voltage drops across the meter.

Key Formulas: $T_d = \frac{1}{2} I^2 \frac{dL}{d	heta}$ — Deflecting torque based on rate of change of inductance; $R = ho \frac{l}{A}$ — Relation between resistance, cross-sectional area, and length

Key Points: Moving iron ammeters are always connected in series with the load.; Thick wire decreases resistance, minimizing the voltage drop across the instrument.; Few turns are used because the current to be measured is large, providing sufficient ampere-turns (NI).; High resistance would cause significant power loss and inaccuracies in circuit operation.

Advantages: Cheap and robust construction.; Can be used for both AC and DC measurements.; Less susceptible to stray magnetic fields compared to PMMC.

Disadvantages: Non-linear scale (cramped at the beginning).; Frequency errors due to changes in reactance.; Hysteresis and eddy current errors.

Applications: Industrial grade AC ammeters and voltmeters.; Switchboard instrumentation.

Additional Info: If the wire were thin, the resistance would be high, leading to a significant voltage drop and potential overheating of the instrument coil.. Option B (Sensitivity) is incorrect because sensitivity is typically defined as Ohms per Volt for voltmeters, not a primary objective for ammeter design.. Option C (Damping) is usually achieved via air friction using a vane attached to the moving system.

Answer: A is correct — A moving iron ammeter requires very low internal resistance to ensure minimal interference with the circuit current when connected in series.

Exam Tip: Always remember: Ammeters should have near-zero resistance (connected in series), while Voltmeters should have near-infinite resistance (connected in parallel).

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