# Find the magnitude of force per unit length exerted by one wire on the other

1. Jul 4, 2009

### mba444

1. The problem statement, all variables and given/known data

Two long straight wires in the xy plane are
parallel to the x axis. One wire is at y =
−8 cm and the other wire is at y = 8 cm. The
current in each wire is 24 A and the currents
are in the negative x direction.
The permeability of free space is 4 π ×
10−7 T · m/A.

Find the magnitude of the force per unit
length exerted by one wire on the other. An-
swer in units of μN/m.

2. Relevant equations

F/L= Uo*ia*ib/(2*pi*d)

3. The attempt at a solution

what i did is that i assumed that one of the wires is at point zero , so i used the equation aboove plugging in these values
F/L= (4*pi*10^-7*24*24)/(2*pi*.08) = i got 1440
which is wrong !!

is there what im doing wrong or is it just a calculation mistake

2. Jul 4, 2009

### Staff: Mentor

What's the distance between the two wires?

3. Jul 4, 2009

### mba444

if i add both the (-8+ 8) i will get zero .. unless i take the magnitude of the of the first so that i get 16

im really not sure =S

4. Jul 4, 2009

### mba444

i used the 16 and i got it right .. therefore thanx for your help DOC AL

5. Jul 4, 2009

### Staff: Mentor

One wire is at -8, the other is at +8. How far apart are they?