0 ×10–5 T and the direction of the field is from
the geographic south to the geographic north A very long straight
conductor is carrying a steady current of 1A What is the force per
unit length on it when it is placed on a horizontal table and the
direction of the current is (a) east to west; (b) south to north Solution  F = Il × B
F = IlB sinq
The force per unit length is
f = F/l = I B sinq
(a) When the current is flowing from east to west,
q = 90°
Hence,
f = I B
  = 1 × 3 × 10–5 = 3 × 10–5 N m–1
This is larger than the value 2×10–7 Nm–1 quoted in the definition
of the ampere