2pr We find that the magnetic
field at a distance r outside the wire is tangential and
given by
B × 2pr  =  m0 I,
B = m0  I/ (2pr)
(4 18)
The above result for the infinite wire  is interesting
from several points of view ANDRE AMPERE (1775 –1836)
Andre Ampere (1775 –
1836) Andre Marie Ampere
was a French physicist,
mathematician and chemist
who founded the science of
electrodynamics