Which of the following meter movements can measure both DC and AC without requiring a rectifier?

The correct answer is that electrodynamic, moving-vane, hot-wire, and thermocouple meter movements can measure both direct current (DC) and alternating current (AC) without the need for a rectifier.

Electrodynamic meters utilize two coils; one coil is fixed while the other moves in response to the magnetic field created by the current passing through them. This allows them to respond effectively to both AC and DC signals due to their design, which does not require rectification for operation.

Similarly, moving-vane meters operate based on the interaction of magnetic fields and can measure both AC and DC by the rotation of a vane. Hot-wire ammeters measure current based on the heating effect of the current flowing through a wire, which can apply to both AC and DC. Thermocouples generate a voltage proportional to temperature differences, and while they are typically used for temperature measurements, they can also respond to current in AC applications.

In contrast, other types of movements mentioned—like galvanometers—primarily measure DC and would require additional circuitry to measure AC. Analog needle movements can refer to typical galvanometer action, which generally evaluates DC; digital display movements often utilize analog signal processing that can require rectification for AC measurements, thus making