# How Do Magnetic Fields Affect Levitating Conductors and Current-Carrying Wires?

• Mspike6
In summary, the first question asks to calculate the magnetic field strength for a levitating copper wire in a strong magnetic field. The solution is given as B=mg/IL, and the question of why the magnetic force and gravitational force are equal is explained. The second question asks whether two parallel wires carrying opposite currents would attract or repel, and the answer is determined using the right hand rule and a relativistic explanation. The conversation concludes with a thank you for the helpful response.
Mspike6
Hi..
I have 2 questions ( simple once i assure you :D) in Electromagntics.

1) ""A 0.120 m long copper wire has mass of 9.02 g and is carrying a current of 5.10 A perpendicular to a uniform magnetic field. This apparatus is placed in a strong magnetic field and the wire is found to levitate. Calculate the magnetic field Strength (B)"

Solution :

I actually solved this one right,
Fm=fg
I L B = Mg
B= mg/I L

What i don't understand is, why do we say that Fm=Fg if the wire Levitate ? i mean... if the why Levitate, it make sense that Fm is bigger (in magnitude) then Fg... why do we equalize them ??

My second questions

"Would two parallel wires carrying a current in opposite directions repel or attract one another?"

I think they would repel. but i don't know why :P

Thank, any help is really appreciated.

As for why |magnetic force| = |gravitational force|-- Simple, if the magnetic force were bigger, the loop would accelerate upwards. Of course, if it did that, it would eventually leave the region of uniform magnetic field. (I think your issue may be with the word 'levitate.' I interpret that as 'hovering at a constant height.')

As for the two wires: If the current is going in opposite directions, the wires would repel. I figured that out by first drawing the wires, then doing the right hand rule to find the magnetic field at the second wire due to the first, then doing the right hand rule again to find the magnetic force on the second wire.

You can also think about it relativistically. An electon in one wire is moving in, say, the positive x direction. The other wire is lorenz contracted, but the electrons in that wire (moving in the negative x direction) are Lorenz contracted more than the stationary protons. The wire appears to have a negative net charge to the electrons in the first wire, and so they repel.

Last edited:
Thanks a lot Maxl..

and ya, i thought levitate means that it has a constant V > 0

Thanks

Thank you for the great question. I love it when people finish their homework but still have questions!

## What is a conductor?

A conductor is a material that allows electricity to flow through it easily due to its high number of free electrons.

## What is a magnetic field?

A magnetic field is a region in space where magnetic forces can be detected. It is created by moving electric charges and can exert forces on other electric charges and magnetic materials.

## How do conductors interact with magnetic fields?

When a conductor is placed in a magnetic field, a force is exerted on the free electrons in the conductor, causing them to move. This movement of electrons creates an electric current in the conductor.

## What is the concept of electromagnetic induction?

Electromagnetic induction is the process of generating an electric current in a conductor by moving it through a magnetic field or by changing the magnetic field around it. This is the principle behind generators, motors, and other electrical devices.

## What factors affect the behavior of conductors in magnetic fields?

The behavior of a conductor in a magnetic field is affected by the strength and direction of the magnetic field, the velocity of the conductor, and the amount of current flowing through the conductor. The material and shape of the conductor also play a role in its interaction with the magnetic field.

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