Physics. Two current carrying wires are parallel to one another and...?

Question

separarted by 1cm., If the distance between them is increased to 2 cm the new force will be what factor times the original force....?

i was thinking either 1/2 or 1/4. please help =]

Answer 1

You will be looking at the inverse square law for the strength of the force that is F varies as 1/d^2.

So if you double the distance from 1 to 2cm then the force will be 1/2^2 = 1/4.

Answer 2

It is 1/2.  The force between parallel wires varies with 1/r.

*******Addendum******

Even though force from a point source varies with 1/r^2, it only varies with 1/r from a line source.  This is because you have to integrate the field over the line.  You need to applying Gauss's law.  ref: http://hyperphysics.phy-astr.gsu.edu/hba...

The easy way to think of it is that the force radiates out from a line charge as a cylinder --unlike a point charge where the force radiates out as a sphere.  The surface area of a cylinder varies with r, whereas the surface area of a sphere varies with r^2.

Here is a confirming textbook cite:  http://142.132.30.225/physics/mag/node10...