Solenoids- A versatile device with multiple uses

Solenoids are a coil of wire wound into a tight helix. The term Solenoid was coined by the French Physicist Andre-Marie Ampere. The term solenoid may have different meanings in different fields of science. In physics, a solenoid often refers to a tightly wound coil whose length is greater than that of the diameter of the coil. There is a core of soft iron inside the coil, and when current passes through the coil, it produces a uniform magnetic field around the solenoid. Here, the solenoid is working as an electromagnet, creating a controlled magnetic field.


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In engineering, the term solenoid usually refers to a transducer device that converts energy into motion (linear). The term solenoid may also refer to an integrated appliance- the solenoid valve of solenoid switch. In the above devices, a solenoid actuates a pneumatic or hydraulic valve or a switch, thus helping us control the device. Examples include the automobile starter solenoid and the solenoid bolts.

Types of Solenoids

There are two types of solenoids:-

  1. Infinite continuous solenoid

  2. Finite continuous solenoid

Infinite continuous solenoid

An infinite continuous solenoid, as the name implies has an infinite length, but a finite diameter. The word continuous here refers to a sheet of conducting material rather that separate coils.

Finite continuous solenoid

A finite continuous solenoid, in contrast with an infinite continuous solenoid, has a finite length and diameter. The term continuous here also refers to a sheet of conducting material rather than different coils.

Uses of solenoids

Solenoids have many uses in physics, engineering, and in everyday life. Following are some uses of solenoids:-

  1. Electromechanical solenoids– Electromechanical solenoids consists of a helical coil of wire with a movable core. The movable core or the armature is free to move in and out of the coil. The armature usually provides mechanical force to another object, for example, a pneumatic valve. The force applied to the armature depends on the inductance of the coil and the current flowing through the coil. Thus, by altering the current flowing through the coil, we can modulate the force applied to the armature. Some examples of electromechanical solenoids include electronic paintball markers, pinball machines, dot-matrix printers and fuel injection systems.

  2. Rotatory solenoids– A rotary solenoid is an electromechanical device that can rotate a ratchet mechanism when power is applied to the solenoid. Rotatory solenoids were first invented during WW II to control the release of bombs from aircraft accurately. However, they are still used in many modern devices.

  3. Pneumatic solenoid valve– A pneumatic solenoid valve is a switch that can route air into any pneumatic device.

  4. Hydraulic solenoid valve– The hydraulic solenoid valve is similar in construction to a pneumatic solenoid valve. The only difference is that these devices control the flow of hydraulic fluids instead of air.

  5. Automobile starter solenoids– As the name implies, these devices are used to start the car. Here, the solenoid receives a large current from the car battery and a small current from the ignition switch. When we turn the ignition switch, a low current pass to the solenoid and the starter solenoid closes a pair of heavy contacts, thus, allowing the larger current from the car battery to start the starter motor.

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