# What is a magnetic field? How were they formed?

Jun 13, 2016

I am not sure that my answer will satisfy you but...

#### Explanation:

A magnetic field is a region of space where, in every point, is present a magnetic force odf the type:
$\vec{F} = q \left(\vec{v} \times \vec{B}\right)$
where $\vec{B}$ is our magnetic field (vector).

Here you can see a similarity with Electric Field where you have:
$\vec{F} = q \vec{E}$

The difference is that the first has the velocity term in it!

We can resume all saying that:
A charge produces around itself an Electric Field $\vec{E}$; if it moves it will also produce a Magnetic Field $\vec{B}$. Both fields will be sensed by the presence of a force.

We can summarize mathematically by writing (for a charge $q$):
$\vec{F} = q \left(\vec{E} + \vec{v} \times \vec{B}\right)$
If the charge is at rest it is ok you get only a E field...if it also moves we add the Magnetic one!

Basically, every time you have a moving charge you have the formation of a magnetic field; for example:
1) around a wire carrying electricity;
2) in a magnetic material; this time caused by the electrons "moving" around in the atoms;
3) in and around a solenoid carrying a current (as in a transformer).

Hope it helps!