Application of the Force on a Current Carrying Conductor in a Magnetic Field - Moving Coil Meter

Light Indicator

A light indicator which has lower inertia  is used to increase the sensitivity of the meter.

Linear Scale

  1. Due to the radial magnetic field and the cylindrical soft-iron core, a linear scale is produced.
  2. A linear scale is more accurate and easier to be read.


  1. A mirror is used to prevent parallax error.
  2. When the observer's eye is exactly above the indicator, the indicator will cover its own image on the mirror. 
  3. This can used to prevent parallax error.

Curved Permanent Magnet

  1. A curved permanent magnet is used to produce a radial field.
  2. A radial field is a magnetic field where the field lines are either pointing away or toward the center of the field.
  3. A radial can be focused by a cylindrical soft-iron core.

Rectangular Coils

  1. When a current flows through the coils, a force will be generated due to the interaction between the magnetic field of the permanent magnet and the coil.
  2. The force will turn the coils, which in turn move the indicator.

Cylindrical Soft-Iron Core

  1. A cylindrical soft iron core is placed inside the radial field produced by the curved magnet.
  2. A soft-iron core can focus the magnetic field of the permanent magnet.

Hair Spring

  1. The deflection of the coil and the indicator stops when the force is balanced by the opposing force from the hair spring.
  2. The angle of deflection is directly proportional to the magnitude of the current in the coil.