How to find direction of mangetic field created by current

[sparkle123]

how to find direction of magnetic field created by toroid

I don't understand how to find the direction of B resulting from a toroid. In the following example from my textbook, the direction of B is found by symmetry arguments are used. (I highlighted this in yellow). Could someone please explain?
Thanks!

 

[Delphi51]

The symmetry argument does not address direction; it merely means the field is the same all around the loop because rotating the loop a few degrees does not change the situation.

The direction is determined by the hand rule. This page has it in the very first diagram:
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/magfie.html#c1
I urge you to find a piece of wire and make a toroid. Then choose a spot on it and wrap your hand around it with your thumb in the direction of the current. Your fingers indicate the direction of the B field. It will go one way inside the coil, the opposite way outside it.

 

[sparkle123]

Thanks! :)