# Electromagnetism: find the laplace force

• jasmine-
In summary, the problem states that the force between two threads of straight currents, undefined, parallel of intensities I and I' of the same direction, must be determined. The student attempted to find the magnetic field that each thread created in a point of the other thread, applying the biot-savart rule, and then applying the laplace rule to find the force applied to a conductor in the presence of a magnetic field. Once they had the equations for the magnetic and laplace forces, they were able to solve for the current I.
jasmine-
Hi every one.

## Homework Statement

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"

## Homework 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.

## 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.

jasmine- said:
Hi every one.

## Homework Statement

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"

## Homework 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.

## 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.

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?

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

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?

jasmine- said:
I actually did not develop any of the equations.all I have is the biot savart equation ,and laplace équation as they were,

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!)

jasmine- said:
I did not understand why velocity?;I have two éqations,the first:http://upload.wikimedia.org/math/7/4/6/7463d12e92a79b39f6b3ac7d44dfe1be.png
the second: the one mentionned here http://fr.wikipedia.org/wiki/Force_de_Laplace
i am sorry,I added links because I don't Know how to write those equations,frthermorenI feel that I have a language problem,

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...

1 person
thank you so much. :)

## 1. What is electromagnetism?

Electromagnetism is a branch of physics that deals with the interaction between electrically charged particles and magnetic fields. It is one of the four fundamental forces of nature, along with gravity, strong nuclear force, and weak nuclear force.

## 2. What is the Laplace force?

The Laplace force is the force that is exerted on a moving charged particle by a magnetic field. It is perpendicular to both the direction of motion and the direction of the magnetic field.

## 3. How is the Laplace force calculated?

The Laplace force can be calculated using the formula F = q(v x B), where F is the force, q is the charge of the particle, v is the velocity of the particle, and B is the magnetic field.

## 4. What is the importance of the Laplace force?

The Laplace force plays a crucial role in many technological applications, such as electric motors and generators, particle accelerators, and magnetic resonance imaging (MRI) machines. It also helps us understand the behavior of charged particles in various natural phenomena, such as the Earth's magnetic field and the auroras.

## 5. How is the Laplace force related to the Lorentz force?

The Lorentz force is the sum of the electric force and the magnetic force acting on a charged particle. The Laplace force is a special case of the Lorentz force, where the electric field is zero, and the particle experiences only the magnetic force due to its motion.

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