# Electro-magnet calculation

#### kosoniscs

How can I calculate a electric-magnet? I mean, I want to built a electric-magnet to raise for example 1kg. I know that the atractive force depends on the current and the number of wires in the coil, as well the quality of the steel in the middle of the coil. But I don't know how can I associate this parameters to an attractive force like 10 Newonts.
Can anybody help?

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#### Nereid

Staff Emeritus
Gold Member
Welcome to Physics Forums, kosoniscs.

#### shyboy

The magnetic force depends on the gradient of the magnetic field:

$$F=m\frac{dB}{dx}$$

(For simplicity I use only one dimension),
here m is a magnetic moment. The magnetic moment itself may be proportional to the external magnetic field strength.
The magnetic field far from the magnet may be considered as a field from dipole. It is more difficult to consider the attraction of two attached magnet. One trick may help. Let's make a small air gap between two magnets. If we find out how much energy we can gain by reducing the air gap, we will find out the force, because
$$F=dE/dx$$

#### kosoniscs

Hi Shyboy...
Could you send me an example?

#### shyboy

A commonly used equation to estimate holding force is:
$$F=0.577B^2 A$$
where B is flux density in kilogauss, and A is the area of a pole face in square inches
http://labcontrol.pqui.utfsm.cl/~wally/Manuals/General/Magnetic/magnetic.htm [Broken]

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"Electro-magnet calculation"

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