Solenoid

A solenoid is an electromagnetic device made out of a coil of wire wound around a cylindrical or elongated core, usually comprised of ferromagnetic material like iron or steel. When an electric current flows through a wire coil, it generates a magnetic field surrounding it, which can exert force on objects in the field or cause mechanical motion. In this article, we will learn in detail about solenoid, its working and application.

Electromagnets are magnets that use electric current to generate magnetic fields. Unlike permanent magnets, which produce a steady magnetic field, electromagnets may be turned on and off by regulating the flow of electricity through a wire coil. They are commonly utilized in applications that demand changeable and regulated magnetic fields. A coil of wire twisted around a magnetic core, usually made of iron or steel, is what makes up an electromagnet. When electric current travels through a wire coil, it produces a magnetic field surrounding it in accordance with Ampère’s law.

A solenoid is a type of electromagnet that consists of a coil of wire wrapped around a ferromagnetic or ferrimagnetic core. When an electric current is passed through the wire, it creates a magnetic field around the core, which results in various applications in industries and everyday devices.

To make a solenoid we need following materials

• Insulated copper wire (preferably enamel-coated)
• Power source (battery or DC power supply)
• Iron or steel rod (optional, as a magnetic core)
• Insulating material (e.g., cardboard tube or plastic pipe)
• Electrical tape
• Wire cutters

The steps to make a solenoid are mentioned below:

• Take a length of insulated copper wire and use wire cutters/strippers to remove any insulation from both ends.
• Make sure the wire is long enough to wrap many layers around the core material you’ve chosen.
• If you’re using a core material (such as an iron or steel rod), place it in the center of the insulating layer.
• Begin winding the wire around the core material, ensuring that each turn is close to the preceding one without overlapping.
• Continue wrapping until there are multiple layers of wire surrounding the center. The magnetic field becomes stronger as the number of turns increases.
• To secure the wire ends to the insulating material, apply electrical tape.
• Turn on the power source to pass current through the wire coil.

When the power is turned on, magnetic field is created which can be tested using iron fillings.

When an electric current is passed through a circular wire, a magnetic field is generated around it. We know that magnetic field is directional, in simpler terms, if we place another circular wire with electric current passing in the opposite direction to that electric current of the first wire, the magnetic fields of both wires will cancel out each other.

However, if the wires have currents passing in the same direction, the magnetic fields around both wires will sum up. Now, a solenoid is like a collection of multiple circular wires, all of which have current passing in the same direction. Its helix-like structure allows for summing up of all the magnetic fields. As a result, a strong magnetic flux is generated when an electric current is passed through this wire.

Can we control the amount of magnetic force? Yes, we can increase the magnetic field in two ways:

1. Increase the current passing through the coil.
2. Increase the number of turns.

This relationship can be given as:

F = ?₀nl

Where ‘n’ is the number of turns of the wire per unit length, ‘I’ is the current flowing through the wire, and the direction can be determined using the right-hand thumb rule.

The magnetic field inside the solenoid is parallel to the axis of the core. Beyond the solenoid, the magnetic field is very weak.

The magnetic field inside the solenoid is parallel to the axis of the core. Beyond the solenoid, the magnetic field is very weak. The purpose of solenoid is to generate a magnetic field, so studying it is very important to understand how magnetic field are distributed around a current carrying solenoid.

Inside the current carrying solenoid, magnetic field are parallel to axis of a solenoid. That is another way of saying that magnetic field is same at all the points inside a current carrying solenoid, that is uniform inside a solenoid. Beyond the solenoid, at very large distance magnetic field is nearly zero.

Formula of Magnetic Field inside a current carrying solenoid

The magnetic field inside a current-carrying solenoid can be calculated using the formula:

[Tex]B = \mu \cdot n \cdot I[/Tex]

Where:

• B is the magnetic field strength inside the solenoid (in Tesla, T),
• [Tex]\mu[/Tex] is the permeability of the material inside the solenoid (in Henry per meter, H/m),
• n is the number of turns per unit length of the solenoid (unitless), and
• I is the current flowing through the solenoid (in Amperes, A).

The derivation of this formula involves considering the magnetic field created by each individual turn of the solenoid and summing up the contributions from all the turns. However, I’ll provide a simplified explanation here.

Consider a solenoid with N turns per unit length, carrying a current I. Each turn of the solenoid acts like a circular current loop, producing a magnetic field at the center of the loop. The magnetic field at the center of a single turn of radius R carrying a current I is given by Ampère’s law as:

[Tex]B_{\text{loop}} = \frac{\mu_0 \cdot I \cdot R^2}{2 \cdot (R^2 + x^2)^{3/2}}[/Tex]

Where:

• [Tex]\mu_0[/Tex] is the permeability of free space (constant, [Tex]4\pi \times 10^{-7}[/Tex] H/m),
• x is the distance from the center of the loop along its axis.

For a solenoid with N turns per unit length and length L, the total number of turns in the solenoid is [Tex]N \cdot L[/Tex]. By symmetry, the magnetic field at the center of the solenoid due to all the turns will be the sum of the magnetic fields from each turn, which gives:

[Tex]B_{\text{sol}} = N \cdot B_{\text{loop}} = \frac{\mu_0 \cdot N \cdot I \cdot R^2}{2 \cdot (R^2 + x^2)^{3/2}}[/Tex]

For a long solenoid [Tex]( L \gg R )[/Tex], the magnetic field at the center of the solenoid can be approximated as constant along the length of the solenoid and is given by:

[Tex]B = \mu_0 \cdot n \cdot I[/Tex]

Where [Tex]n = N/L [/Tex] is the number of turns per unit length of the solenoid.

Here are the differences between a solenoid and a bar magnet.

There are different types of solenoid for different purposes. Following are the major types of solenoid along with a small description for each.

AC-Laminated Solenoid

An AC-Laminated solenoid is like a small, powerful magnet that can turn on and off really quickly. It’s made up of a special metal core surrounded by a coil of wire. This coil is made of many thin layers, or laminations, of metal. These layers help control where the electric current flows, making the solenoid work efficiently. AC-Laminated solenoids are often used in things like doorbells and buzzers.

DC-C Frame Solenoid

It is a C-shaped frame wrapped around with a coil of wire. When electricity flows through the coil, it creates a magnetic field that moves a metal piece inside the C-shape. This type of solenoid is great for things that need a quick and strong push or pull, like in some machines and tools.

DC-D Frame Solenoid

The DC-D Frame solenoid looks a bit like the letter “D.” It’s made of two pieces of metal frames that are put together to form a D-shape around the coil of wire. When electricity flows through the coil, the magnetic field moves a metal piece inside the D-shape. This type of solenoid is also used for strong pushes and pulls, just like the C-frame solenoid.

Linear Solenoid

A linear solenoid is a bit different. It has a coil of wire wrapped around a metal core that can move back and forth. When electricity flows through the coil, it creates a magnetic field that pushes or pulls the core. This type of solenoid is used in things like car door locks and valves, where you need something to move in a straight line.

Rotary Solenoid

The rotary solenoid is special because instead of moving back and forth, it can turn like a wheel. It still has a coil of wire and a core, but the way it’s built allows it to rotate. This type of solenoid is used in things like electric locks and valves, where you need something to turn automatically.

Each type of solenoid has its own special job to do, but they all work in a similar way by using electricity to create a magnetic field that can move things.

The applications of solenoid are mentioned below:

• Door locking mechanisms: Mechanical model in which circuit of solenoid is completed when correct combination of keys are aligned.
• MRI machines: Function of solenoid in MRI machines is to generate magnetic field required for imaging process.
• Mechanical or fluid control valves: With help of its magnetic property, solenoids are used to control opening and closing of mechanical and fluid valves.
• Motors and Generators: Solenoid act like initiating-mechanism for motors and generators. They are used to create magnetic fields in solenoid.

In short, electromagnets and solenoids are crucial in lots of things we use every day, like electric motors and magnetic locks, as well as in important medical technologies like MRI machines. We learnt the functionality of solenoids and how we can create our own. Further we looked at different types of solenoids and various kind of applications of them. Understanding functionality of solenoid is important milestone in understanding of both – physics and engineering.

Also, Check

• Magnetic Field due to Current carrying Conductor 
• Bar Magnet as an Equivalent Solenoid
• Magnetic Field Due to Solenoid and Toroid

What is Solenoid?

A solenoid is a type of electromagnet which consist of a coil of wire wrapped around a ferromagnetic or ferrimagnetic core. When an electric current is passed through the wire, it creates a magnetic field around the core, which result in various applications in industries and everyday devices.

What kind of material is used for the core of electromagnets?

The core of electromagnets is made up of Ferromagnetic or Ferrimagnetic material.

Can we control magnetic force generated from solenoid?

Magnetic force generated from a solenoid can be controlled in two ways

1. Increase electric current :- Electric current in coil is directly proportional to Magnetic force.
2. Increase the number of turns of the wire per unit length :- The number of turns is also directly proportional to magnetic force.

What is relation of magnetic field and electric current in solenoid ?

The relation between magnetic field and electric current in solenoid is given by the formula F = ?₀nl

What are applications of solenoid?

Solenoids have various applications across different industries. Some common applications are:

• Door locking mechanisms
• MRI machines
• Mechanical or fluid control valves
• Motors and generators.