Which of the following best describes a current coil in a meter?

• A. Small number of turns of large wire
• B. Large number of turns of small wire
• C. Large number of turns of large wire
• D. Small number of turns of small wire

Answer: (B)

The essential idea is that a meter’s sensitivity depends on how effectively the coil converts current into a magnetic moment. In a moving-coil meter, the torque on the coil is proportional to the number of turns times the current (N × I) in the fixed magnetic field. To detect small currents, you want many turns so that even a tiny current creates a large magnetic moment and a noticeable deflection. Using many turns of fine (small-gauge) wire lets you pack more turns into a compact coil, increasing N without requiring a large current, while the fine wire helps keep the coil’s resistance manageable and the heat drop acceptable. If you had only a few turns or used thick wire, the magnetic effect would be too small for the same current, making the meter far less sensitive.