Question

Find the force per unit length between two infinite, parallel, current-carrying wires with currents i1; i2 respectively and separated by a distance d

Answer 1

magnetic field due to wire 1 on 2 is. B1=u i1/ 2pie d
Force on 2 due to 1 = i2×B1× l acting towards 1
F/l = u × i1 × i2/ 2 ×pie× d.
u= magnetic const= 4 pie