The magnitude of the magnetic field is,
–7
2
0
–1
4
10
10
1
2
2
10
NI
B
µR
π ×
×
×
=
=
×
4
2
10−
=
π ×
4
6 28
10
T −
=
×
4 6  AMPERE’S CIRCUITAL LAW
There is an alternative and appealing way in which the
Biot-Savart law may be expressed Ampere’s circuital law
considers an open surface with a boundary (Fig