Concept:Moving coil instruments are classified into two main types based on their construction and operating principle.
They include the permanent magnet moving coil type and the dynamometer type.
Explanation:The permanent magnet moving coil instrument uses a fixed permanent magnet and a movable coil.
It can measure only direct current and direct voltage.
The dynamometer type instrument uses fixed and movable coils instead of a permanent magnet.
It can measure both direct and alternating current and voltage.
Both types work on the principle that a current-carrying conductor placed in a magnetic field experiences a mechanical force.
The resultant magnetic field produced by the movable current-carrying coil tries to align with the main field.
This produces a deflecting torque that moves the pointer over the scale.
Answer:Thus, moving coil instruments are both permanent magnet and dynamometer types.
The correct option is A.
