Solenoid and Toroid

What is a Solenoid?

A solenoid is nothing but a coil of wire that adopts magnetic properties when electricity passes through it. A solenoid wire is wrapped around a metallic core. To clarify solenoid meaning further, consider that electricity changes to magnetism, which again transforms to electricity. 

The diagram shows how a solenoid functions when electricity flows through it.

Since solenoid has immeasurable length, the magnetic field when current passes through it is equal along this element. Therefore, a solenoid allows even a very small electrical components to do a tremendous amount of work. One can calculate the magnetic field using a simple mathematical formula.

F = µ0nI

Here, n refers to the number of wire turns per unit length. I is the amount of current that flows through the solenoid wire. You can derive the direction of magnetic field flow using the right hand-thumb rule.   

Different Types of Solenoid

After understanding solenoid meaning, you must venture to learn more about the various types of a solenoid. Although electric principles remain the same for all solenoids, their design, function and material tend to differ. Some of the common solenoids in use are:

  • DC D-Frame Solenoid

  • AC Laminated Solenoid

  • DC C-Frame Solenoid

  • Rotary Solenoid

  • Linear Solenoid

What is Toroid?

A toroid has a similar shape when compared to a solenoid, but is bent into a ring structure. This doughnut-shaped structure is wound with copper wire. Generally, one can create toroids using ferrites or powdered iron. Toroid definition in physics states that it can generate a magnetic field based on the permeability of the ring’s material.

Figure 2.0 depicts a toroid, where B represents the magnetic field flowing inside the closed-loop.

The magnetic field, both outside and inside a toroid, is zero. The direction of magnetic field inside the turn of a toroid is always clockwise, according to the right-hand thumb principle. The equation of magnetic field inside a toroid can be calculated from the equation – 

B = µNI/2πr

You can derive this equation using Ampere’s law. N is the number of times the coil of a toroid turns, while r refers to the toroidal radius. Lastly, I is the amount of current flowing through this device.

Simply understanding toroid and solenoid meaning are not sufficient. Here is a look at some of their differences.

Difference Between Solenoid and Toroid



Cylindrical shape

Circular shape

Magnetic field forms outside 

Magnetic field forms within

Magnetic field is uniform inside it. 

Non-uniform magnetic field

Magnetic field B = µ0nI

Magnetic field inside is 0

Magnetic field outside is 0

Magnetic field within or B = µNI/2πr

Similarities Between Toroid and Solenoid

Apart from solenoid and toroid differences, these devices are also similar in a few ways. These are as follows – 

  • Both rely on the principles of electromagnetism to function properly.

  • Magnetic fields created by a solenoid and within a toroid are always equal.

  • With the passage of electricity, both of these acts like electromagnets

Applications of Solenoid

Solenoids are used in a variety of modern-day applications. Some of these are listed below – 

  • Inside locking mechanism for office doors, controlled electronically. These doors remain locked until current continues to flow in the mechanism. However, if you switch the electricity off, the door swings open.

  • Solenoids are crucial parts of some medical devices. For instance, a solenoid is a vital portion of a dialysis machine, effectively controlling blood flow. 

  • It is also commonly found in industrial operations as well, especially in devices used for pinching, rotating, holding and more.

If you are still unclear about toroidal meaning, you can clear your doubts by attending our online classes. Our experienced teachers are well versed in physics. Furthermore, now you can also download our Vedantu app for easier access to study materials and interactive online sessions.

FAQ (Frequently Asked Questions)

1. What is the Nature of Magnetic Field Inside a Solenoid?

Ans. A magnetic field inside a solenoid is always uniform, meaning that it exhibits the same magnetic force throughout all parts of the coil.  

2. Is a Magnetic Field Inside a Solenoid Uniform or Non-Uniform?

Ans. Magnetic field inside a solenoid is uniform. However, this is not the case for toroids, where the magnetic field is usually non-uniform in nature.

3. What is a Solenoid in Physics?

Ans. A solenoid is a cylindrical device with copper wires wound around it. Solenoids assume magnetic properties when an electric current passes through it.