Factors Affecting the Magnetic Field of a Coil

Electrons flow in a wire or conductor, whenever this happen, a magnetic field is present. A way to strengthen the magnetic field is by bending the wire to form a loop and stronger when these loops of wire are wound close together forming a coil or solenoid. Unlike bar magnets, the magnetic field in a coil can be turned on and off and its magnetic field strength may be changed due to some factors. These factors include the following:

  1. current in the coil;
  2. number of loops in the coil; and
  3. types of core material.

Current in the Coil

When electrons flow through the coil, magnetic field will be present in the surrounding, this means to say that, the magnetic field strength varies directly as the current through the coil. The greater the current, the greater also the magnetic field strength. If the field will be represented by magnetic field lines, the greater the current, the magnetic field lines will be closer to each other.

Number of Loops

Magnetic field is produced in every loop of wire. Since a coil is a group of loops of wire, it then follows that the magnetic field in a coil is the total magnetic field of each loop. Thus, the more number of loops, the stronger the magnetic field will be. The magnetic field strength is directly proportional to the number of loops.

Type of Core Material

The type of material used as core in a coil also affects the magnetic field strength. The atomic dipoles of the core material align with the coil’s magnetic dipole, and will become an induced magnet making an increase in the magnetic field strength. The factor by which the core material increases the magnetic field strength is called as magnetic permeability, \mu. It is obtained by the ratio

\mu = {\text{magnetic field strength in material} \over \text{magnetic field strength in vacuum}}.

The magnetic field strength is directly proportional to the permeability of the core material.

Core materials are grouped into three based on their permeability, they are – ferromagnetic, paramagnetic, and diamagnetic materials.

Ferromagnetic materials have very high permeability. These materials become very strong induced magnets when used as core materials in a coil. Some examples of ferromagnetic materials are cobalt, iron, nickel, and their alloys.

Paramagnetic materials cause very slight increase in the magnetic field of a coil when used as core. Their permeabilities are only slightly greater than 1. Oxygen and aluminum are examples of this kind of material.

Diamagnetic materials have permeabilities slightly less than 1. As core, they cause a slight decrease in the coil’s magnetic field. copper, silver, and water are considered as diamagnetic.