# Buiding an electromagnetic field

#### baby_1

Joined Jun 3, 2011
39
Hello
i want to create an electromagnetic filed that can move a object with a a weight.could you explain me how can i do that and what is the formula?

#### panic mode

Joined Oct 10, 2011
1,865
piece of cake, you are going to need:
F=ma

and Maxwell's equations:

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#### panic mode

Joined Oct 10, 2011
1,865
you may find these useful too
(Physics I)

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#### panic mode

Joined Oct 10, 2011
1,865
and this can't hurt either (sorry, can't find one for electromagnetics II)

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#### pilko

Joined Dec 8, 2008
213
The force you are looking for is called the MAGNETOMOTIVE FORCE or MMF.
MMF = Current X Number of turns.

pilko

#### baby_1

Joined Jun 3, 2011
39
Thanks panic mode
but i can understand what should i do?
for example i want to move a 1kg object and now that the diameter of wire.how can i calculate the number of round , core and formula that show me the relationship between this formula and the weight of object

#### pilko

Joined Dec 8, 2008
213
There are several factors effecting the force required.
- Distance from magnet to load
- Material of load
- Shape of load
- Atraction or repulsion?

pilko

#### Wendy

Joined Mar 24, 2008
22,176
Electromagnetic radiation is not going to be of much help I'm afraid, though magnetic forces could get you there (as in electromagnet).

#### baby_1

Joined Jun 3, 2011
39
Thanks mr.Marsden
could you help me on magnetic force?how can i do it with a dc voltage

#### panic mode

Joined Oct 10, 2011
1,865
force developed by magnetic field must exceed force of gravity (weight of object) in order to cause lift. But this means that target object must have own magnetic field in order to interact with field you create externally.
W=m*g

where
m=mass of object (kilograms)
q=acceleration due gravity (9.8m/s^2)
W=weight (Newtons)

Btw, everything you need is in (or can be derived from) equations I posted.

in general, force on conductor in magnetic field is:
F=I*LxB (this is direct result of F=q*vxB)

where 'x' is cross product
I is current in a conductor
L is length of conductor
B is magnetic field vector in region where conductor is
q is charge
v is velocity vector (note that his is VECTOR, it has magnitude and direction).

or simply

F=B*I*L*sin(θ) (here using magnitudes only)

where
θ is angle

this is for single conductor, normally you would use coil with multiple turns where N is number of turns of wire. using multiple turns we can increase magnetic field of repelling coil.

Btw
B=μH (so using ferromagnetic core with high μ helps)
from Ampere's Law we get
Integral H*dL = I
and as mentioned before using multiple turns your effective current increases to N*I

DC voltage is nothing. it is only needed to exceed resistance of the wire in your coil so you get current you want. Current is everything.

#### ceidas

Joined Dec 26, 2011
50
But this means that target object must have own magnetic field in order to interact with field you create externally.
What? You want to say that when I am taking a magnet and lift in the air some iron needles, the needles already had some magnetic field of their own?

#### panic mode

Joined Oct 10, 2011
1,865
no, that is attractive force.

it was never specified that objects to be lifted are ferromagnetic and if lift has to be gentle or if it is ok to result in collision.

btw. if those needles never develop their own magnetic field (such as induced magnetic field), you will not be able to pick them with a magnet. there... ;p

#### Brownout

Joined Jan 10, 2012
2,390
@baby1,

I think I understand your question. All of the answers that have been given are great for calcualting MMF and so forth, but I think you want to know what force would act on an object that results from the MMF or magnetic field. Unfortunatly, I don't have the answer. Once or twice I tried to find out, but always came up short. That best answer I can give is to use the equations given to maximize the field strength, MMF, and the experiement with different objects. Please report your results. I have an interest in this too.

#### ceidas

Joined Dec 26, 2011
50
no, that is attractive force.

it was never specified that objects to be lifted are ferromagnetic and if lift has to be gentle or if it is ok to result in collision.

btw. if those needles never develop their own magnetic field (such as induced magnetic field), you will not be able to pick them with a magnet. there... ;p
Firstly, I know four forces in the nature. Gravity, electromagnetic and nuclear. I dont know that "attractive force" of yours.

Secondly, you said "that target object must have own magnetic field in order to interact with field you create externally". If you take two metals and bring them together, will you observe any magnetic interaction? No. But if you bring them close to a magnet and then force an interaction between them, will you see any difference? Yes, because now their magnetic domains are not messed up.

So, the needles didnt have any magnetic field, they got it after the interaction with the magnet.

#### panic mode

Joined Oct 10, 2011
1,865
"target must have field to interact" so what?
where does it say that own field has to exist before object is excited?

you may want to recount those four forces.

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#### ceidas

Joined Dec 26, 2011
50
"target must have field to interact" so what?
where does it say that own field has to exist before object is excited?

you may want to recount those four forces.
You said that a field has to exist in order for the object to interact and I am saying that this is not correct.

Why do I want to recount the four forces?

#### Wendy

Joined Mar 24, 2008
22,176
Firstly, I know four forces in the nature. Gravity, electromagnetic and nuclear. I dont know that "attractive force" of yours.

Secondly, you said "that target object must have own magnetic field in order to interact with field you create externally". If you take two metals and bring them together, will you observe any magnetic interaction? No. But if you bring them close to a magnet and then force an interaction between them, will you see any difference? Yes, because now their magnetic domains are not messed up.

So, the needles didnt have any magnetic field, they got it after the interaction with the magnet.
Electric force and magnetic forces can be combined to make electromagnetic, but they also exist separately.

#### ceidas

Joined Dec 26, 2011
50
Electric force and magnetic forces can be combined to make electromagnetic, but they also exist separately.
Actually, when I said electromagnetic I meant the force an electric field and a magnetic field can cause, but since they are closely related to each other I simply mentioned them as electromagnetic force.

#### WBahn

Joined Mar 31, 2012
26,301
Generally the four fundamental forces that act at a distance are given as the gravitational, the electromagnetic, the strong nuclear and the weak nuclear forces.

I recall in E&M II when, after nearly a semester of calculating magnetic fields, the professor came in and said, "Today I will show you that there is no such thing as a 'magnetic field'." and then proceeded to prove it.