Permeability (electromagnetism) facts for kids
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Gyrator-capacitor model variables
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Permeability is a way to describe how easily a material lets a magnetic field pass through it. Think of it like how easily water flows through a sponge. Some materials let magnetic fields pass through them very easily, while others resist them.
What is Permeability?
Imagine you have an electric current flowing through a wire. This current creates a magnetic field around the wire. If you put different materials near this wire, the magnetic field inside those materials will change. Permeability tells us how strong or "dense" that magnetic field becomes inside a material.
Materials with high permeability can concentrate magnetic fields. Materials with low permeability don't let magnetic fields pass through them easily.
Measuring Permeability
Permeability is measured in units called henries per metre (H/m). Its special symbol is 
(pronounced "myoo").
Empty space, or a vacuum, has a fixed permeability. This is called the permeability of free space and its symbol is 
. Its value is very small, about 0.0000004 times π.
Relative Permeability
Because the permeability of empty space is a constant, we often talk about a material's relative permeability. This is shown by the symbol 
.
Relative permeability compares a material's permeability to the permeability of empty space. You can find it by dividing the material's permeability () by the permeability of free space (). So, 
.
For most everyday materials, their relative permeability is very close to 1. This means they behave almost like empty space when it comes to magnetic fields. Because of this, we often just use the permeability of free space for many calculations.
Special Materials
There are some important exceptions to this rule. These are materials called ferromagnetic materials. These materials are very good at concentrating magnetic fields.
Examples of ferromagnetic materials include iron and nickel. Iron can have a relative permeability of 5000, and nickel around 600. This means they can make a magnetic field thousands of times stronger than in empty space.
Scientists and engineers have even designed special materials. These materials can have a permeability more than a million times larger than empty space. They are very useful in things like transformers and electromagnets.
