Question 6A519

The D'Arsonval type meter, also known as a Permanent Magnet Moving Coil (PMMC) meter, operates on the principle of electromagnetism. It utilizes a **permanent magnet** to create a fixed magnetic field. Within this field, a **movable coil** is suspended, typically on low-friction **jewel bearings**, and has a **pointer** attached. When current flows through the coil, it generates its own magnetic field, which interacts with the permanent magnet's field, producing a torque that causes the coil and pointer to rotate. To ensure the deflection is proportional to the current and the pointer returns to zero, **two spiral springs** are attached to the movable coil. These springs provide the necessary restoring force, opposing the magnetic torque and allowing the pointer to settle at a specific position corresponding to the current being measured. Therefore, both the permanent magnet and the assembly of the movable coil, pointer, jewel bearings, and spiral springs are essential components for a functioning D'Arsonval meter.