The magnitude of the magnetic field at a distance R from a long,
straight wire carrying a current I is given by:
π
0
2
I
B
R
µ
=
The field lines are circles concentric with the wire 8 The magnitude of the field B inside a long solenoid carrying a current
I is
B = m0nI
where n is the number of turns per unit length where N is the total number of turns and r is the average radius