# Magnetic Fields

Gold Member
Hi. Im having a little trouble grasping the concept of a magnetic field. My book doesnt explain it very well.

I understand that any magnet has a magnetic field, which is the space around it in which other magnets are subject to a force due to the magnet.

What im having trouble with is concepts of magnetic flux and magnetic flux density. From what ive read, magnetic flux density is a number of field lines per unit area (where the field lines are perpendicular to the area). What im not understanding is how a number can be assigned for the number of field lines passing through an area. I thought the idea of field lines were invoked for the simplicity in graphically representing magnetic fields. I would have though that in an actual magnetic field, the number of actual field lines would be infinite for any given area.

Is somebody able to clear up this misconception?

Dan.

Hi Dan,

You're right. The concept of field lines and flux density is all really abstract. Its not meant to be literal when they say flux density B is the number of field lines per unit area. (Since you don't really measure field lines in numbers; its measured with units tesla). Its just so that when we're looking at a diagram, we can say that a particular spot has greater B when the density of lines is greater. Sort of like the closer the lines are together, the stronger the field.

Does that help?

Kurdt
Staff Emeritus