http://www.ck12.org Chapter 15. Magnetism Version 2
Sometimes, it is necessary to represent such three dimensional fields on a two dimensional sheet of paper. The
following example illustrates how this is done.
In the example above, a current is running along a wire towards the top of your page. The magnetic field is circling
the wire in loops that are pierced through the center by the current. Where these loops intersect this piece of paper,
we use the symbol
⊙
to represent where the magnetic field is comingout of the pageand the symbol⊗
to represent
where the magnetic field is goinginto the page.This convention can be used for all vector quantities: fields, forces,
velocities, etc.