# Magnetic Field of a Coil w/ N Spire: Determining Off-Axis Fields

• cataldo
In summary, the conversation discusses the possibility of determining the magnetic field of a coil at a point that is not on the central axis of the coil. This topic is covered in advanced textbooks such as "Classical Electromagnetism" by Franklin, which uses methods such as expanding the magnetic scalar potential in Legendre polynomials and using elliptic integrals.
cataldo
Hi everybody. I have a question on a magnetic field of a coil with N spire . I know the magnetic fields on point P that it has a about distance form coil center and staies on the central axis of the coil. Is possibile to determinate the magnetic filed of the coil on point P that does not stay on central axis of the coil? For example the point P staies on axis that has a distance above o below from central axis of the coil.
Sorry if i do not write a perfect english...
Best regards

That is done in advanced textbooks.
The simplest is to expand the magnetic scalar potential in Legendre polynomials.
Another method leads to elliptic integrals.

Hi clem. tanks for your replay..
Can you suggest some advanced textbook where i found this topic?

"Classical Electromagnetism" by Franklin does this in Sec. 7.10.1 using Legendre polynomials.

## 1. What is a magnetic field?

A magnetic field is an invisible force created by moving electric charges or magnetic materials. It exerts a force on other magnetic materials and can be visualized using field lines.

## 2. How is the magnetic field of a coil with N spires determined?

The magnetic field of a coil with N spires can be determined by using the equation B = μ0 * N * I / L, where B is the magnetic field strength, μ0 is the permeability of free space, N is the number of spires, I is the current flowing through the coil, and L is the length of the coil.

## 3. What is an off-axis magnetic field?

An off-axis magnetic field is a magnetic field that is not aligned with the axis of the coil. This can occur when the magnetic field is measured at a point that is not directly in line with the center of the coil.

## 4. How does the number of spires in a coil affect the magnetic field?

The number of spires in a coil directly affects the strength of the magnetic field. As the number of spires increases, the magnetic field strength also increases.

## 5. What are some applications of understanding off-axis magnetic fields?

Understanding off-axis magnetic fields is important in many industries, such as in the design of electric motors, generators, and transformers. It is also crucial in medical imaging technologies such as MRI machines and in research and development of new magnetic materials.

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