What Is Solenoid And How It Works?


Before we dive in deep into the principles of a  solenoid, let’s get a basic understanding of what an electromagnet is.

An electric current flowing through a coiled wire creates a magnetic field. When this wire is wound around a ferromagnetic or ferrimagnetic material, a magnet is created  known as an electromagnet. Since a magnetic field is produced as long as the current exits in the wire, the subsequent electromagnet has a temporary magnetic effect. When the current decreases to zero, there will be no magnetic effect.


Derived from two Greek words: Solen (pipe) and Eidos (coil), the solenoid is a type of an electromagnetic device that converts electrical energy into mechanical energy. It is generally made by tightly wounding wires in a helix shape around a piece of metal. Whenever an electric current passes through it, a magnetic field is created.

As previously stated, the power of the magnetic field depends on the electric current. Therefore, by varying the current as per our need, we can easily magnetise and demagnetise the electromagnet, enabling us to control the magnetic fields for different requirements.

Courtesy: Wikipedia

Working Principle

A solenoid works on electromagnetism and electromagnetic force. It consists of a round cylindrical coil that has several number of wire turns, and a metal rod inside the coil that is free to move. When an electric current is provided to the coil, a magnetic field is generated due to which the metal core or rod inside the coil gets attracted due to towards the drection where the magnetic flux is high. This electromagnetic effect in a solenoid enables any connected plunger or armature to move as per our need. 

In this way, we can control the magnetic field of a coil by controlling and in turn use it for controlling the mechanical movement of metal core.

The formula for the magnetic field in a solenoid is:


where B= Magnetic field

         µ= Permeability

               N = number of turns

         I = current of coil

      L= length of coil

Turns density, n= N/L (Number of turns per unit length)

So from this formula we can see that to increase the magnetic force produced in a solenoid coil, we will have to increase the number of turns, N and the current, I.

Types Of Solenoid

AC Laminated Solenoid

It has a very high initial attracting force and very short closing time. It is made with a laminated metal or insulated thin sheets that are individually ,assembled.

DC-C Frame Solenoid

As its name states, this solenoid is constructed in such a way that it has a letter ‘C’ like frame cover around the coil. This type is widely used in gaming machines.

DC-C Frame Solenoid
DC-C Frame Solenoid

DC-D Frame Solenoid

As its name says, this solenoid has a coil that is covered by two ‘D’ frames on two sides. This types is generally used in AC power applications.

DC-D Frame Solenoid

Linear Solenoid

This type of solenoid has a freely movable steel or iron rod called plunger inside a round cylindrical shaped coil. The iron rod is allowed to freely move in or out of the cylindrical coil depending on the current applied.

Linear Solenoid
Linear Solenoid

Rotary Solenoid

It is a special type of solenoid where the magnetic force is converted into a rotational force or a rotary motion. It consists of an armature core mounted on a flat disk.
When a current is provided, the armature gets attracted towards the stator and the flat disk rotates.


Solenoid Valve

The solenoid valve is a simple device in which a solenoid is used for controlling and regulating the flow of fluid. It has a coil with free movable plunger or an iron rod with a spring inside it. When we energise the coil, the plunger moves from its position due to magnetic attraction and when we cut the power to coil, the plunger comes back to its original position with the help of a spring. As soon as the plunger comes in the path of the flowing fluid, its flow stops.

Solenoid Valve
Solenoid Valve

Solenoid Lock

Here we use the movement of solenoid plunger for the locking and unlocking mechanism. These solenoid locks are widely used in electronic and biometric password-based locks. It consists of a strong metal plunger that can move. When the coil gets magnetised due to an electric field, the plunger moves to perform the lock and unlock mechanism.

Solenoid Lock
Solenoid Lock

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