Two long straight vertical wires X and Y pass through a horizontal card, as shown in the figure below.
The current in each wire is in the upward direction. The top view of the card, seen by looking vertically downwards at the card, is shown in the figure below.
The magnetic flux density 
at a distance 
from a long straight wire due to a current 
in the wire is given by the expression
where 
is the permeability of free space. The current in wire X is 
and that in wire Y is 
. The separation of the wires is 
.
Calculate the force per unit length on wire Y due to the current in wire X.
The currents in the wires are not equal. State and explain whether the forces on the two wires are equal in magnitude.
.
