# Homework Help: Magnetic Force Formula

1. May 18, 2005

### ccflyer

Hi everyone, I am trying to learn about electromagnets for a project I am working on and I need to know how much magnetic force (in Teslas) that I would need to lift a given weight. Would anyone be able to point out a formula that I would be able to use?

Any help would be greatly appreciated!

-ccflyer

2. May 19, 2005

### HallsofIvy

First, a Tesla is NOT a unit of magnetic force- it is a unit of magnetic flux density- the flux density that will result in a 1 Newton force acting on a one coulomb charge moving at one meter per second perpendicular to the magnetic flux direction.

So no one can tell you "how many Teslas" you need to lift a given weight- it depends on much more than weight. Of course, you would start by expressing your weight in Newtons- that's the force you need. Now you would need to figure in the magnetic properties of the material you are lifting- that's going to be the hard part. The same magnetic field will result in different forces on different kinds of metals.

3. May 19, 2005

### ccflyer

alright, I get what you are saying, and I guess that makes sense, but would you be able to point me in the direction of a formula?

Last edited: May 19, 2005
4. May 19, 2005

### Pyrrhus

Well magnetic force is defined as

$$\vec{F}_{b} = q \vec{v} \times \vec{B}$$

where q is the charge, B is the magnetic field, and v is the velocity of the charge.

5. May 19, 2005

### dextercioby

No,no,big confusion.The Tesla (apud Nicolo Tesla) is a unit for MAGNETIC FIELD INDUCTION,commonly noted by $\vec{B}$,which is a pseudovector.

See post #7.

Daniel.

Last edited: May 20, 2005
6. May 20, 2005

### HallsofIvy

This is what I found at http://www.answers.com/topic/tesla
"The unit of magnetic flux density in the International System of Units, equal to the magnitude of the magnetic field vector necessary to produce a force of one newton on a charge of one coulomb moving perpendicular to the direction of the magnetic field vector with a velocity of one meter per second. It is equivalent to one weber per square meter. "

7. May 20, 2005

### dextercioby

It's not called "magnetic flux density",but "magnetic induction".

$$\Phi_{mag}=:\iint_{S} \vec{B}\cdot d\vec{S}$$

,so indeed the magnetic induction is the magnetic flux density.But the first name is the correct SI one.

Daniel.