# Electromagnetism: find the laplace force

1. Mar 23, 2014

### jasmine-

Hi every one.
1. The problem statement, all variables and given/known data
in french,the problem says:"déterminer la force de laplace qui s'exerce entre deux fils de courants réctilignes,indéfinis,parraléles d'intensités I et I' de meme sens".maybe in english it means:"find the laplace force that is applied between two threads of straight currents,undefined,parallel of intenisties I and I' of the same direction"

2. Relevant equations
the problem is that in class,we have learned what is the magnetic force that is applied by a thread in a certain point M ,but what about the force applied by a thread on a thread,I think that there will be probably some integrals or some sommations bt I don't know how to do it.

3. The attempt at a solution
i tried first to find the magnetic field that each one of these two threads creats in a point of the other thread appling the biot-savart rule,then nafter finding these two forces I will apply the laplace rule,that says that there is a force applied to a conductor in the presence of a magnetic field.the one i was supposed to find before.thanks.

2. Mar 23, 2014

### Staff: Mentor

Welcome to the PF.

You are on the right track. That is how you find the force on a wire from the magnetic field created by another parallel wire. Can you show us your work on the equations?

3. Mar 23, 2014

### jasmine-

I actually did not develop any of the equations.all I have is the biot savart eqation ,and laplace équation as they were,

4. Mar 23, 2014

### jasmine-

Each wire creats a magnetic field in a point M of the other wire,as the number of the points if infinite,how could we find the whole mahnetic field?

5. Mar 23, 2014

### Staff: Mentor

Write the Biot-Savart equation for the B-field generated by wire 1, at the position of wire 2.

That gives you the "B" part that you need for the Lorentz Force. What is the equation for the Lorentz Force, in terms of the B-field and the charge and velocity?

How can you define current I in terms of charge and velocity...?

(Thats a lot of hints!)

6. Mar 23, 2014

### jasmine-

7. Mar 23, 2014

### Staff: Mentor

Here is a tutorial post about how to write LaTeX equations, which will make your posts much easier to read and reply to:

https://www.physicsforums.com/showpost.php?p=3977517&postcount=3

And the 2nd link you posted does show an equation with the current I instead of having to work the original equation which deals with charge density and drift velocity. Those two links with their equations should be what you need to solve this problem. Check out the LaTeX tutorial, and post your equations here to work toward the solution...

8. Mar 23, 2014

### jasmine-

thank you so much. :)