Solenoid

Some Solitary Facts about Solenoid

The term solenoid is one to be commonly found in the study of physics as well as in connection with electrical appliances. Basically, solenoid is the name given to a tightly wounded coil in the shape of a helix. To be more technical, it refers to a thin loop of wire circling a metallic nucleus.

An electromagnet is produced when current is supplied to the wire. Solenoids are commonly used for the purpose of creating controlled magnetic fields. In fact, solenoid is synonymous with a magnet used for the purpose of creating a uniform magnetic field, in which experiments are to be carried out.

Solenoid and Magnetic Fields

The magnetic field inside a solenoid is radially homogenous in nature and is independent of the distance from the axis or the cross-sectional area of the solenoid. However, it should be borne in mind that the longitudinal magnetic field is free to vary.

Similar to the magnetic field inside of the solenoid, the outside magnetic field is also uniform radially. However, this is true only in case of the magnetic field near to the centre of the solenoid.

Towards the outside of the field, the flux density will be almost equal to zero, resulting in the radii of the field approaching towards infinity. The magnetic flux density of a solenoid is calculated by the formula  where μ0 is the magnetic constant, N the number of turns, i the current and l the length of the coil.


A table showing the inductance of solenoids of various lengths has been made by Dellinger, Whittmore and Ould. Inductance of solenoids that have a more complicated structure can be calculated by Maxwell’s Equation. Within certain restrictions, the same rule can also be applied to calculate the inductance of solenoids that have magnets in their cores instead if metals.

Uses of Solenoids

A solenoid can be used in a variety of ways depending on its type. While electrochemical solenoids are mostly used in paintball markers, pinball machines, dot matrix printers and fuel injectors, rotary solenoids are used to rotate a ratcheting mechanism when power is applied.

This type of solenoid was also used for making the bomb shackles during the Second World War. Besides these, solenoids are also used for controlling pneumatic and hydraulic valves, making disk drives as well as starter equipments of automobiles.

The last mentioned item can either have a separate solenoid connected to it or have the solenoid built within the system.