Is there an equation relating electromagnetic force and the distance over which it can attract an object?

Question

I.e. like how those electromagnets in scrap yards pick up junk, i was wondering if there is any kind of relationship that governs the strength of the magnet and how far away it can be from the object its attracting so that it will jump up to attach itself to the magnet. any suggestions?

Answer 1

Theoretically a magnet attracts an object over an infinite distance. The attraction drops off as the square of the distance and the attraction is directly proportional to the strength of the magnet, usually defined in "gauss" units. Whether an object will move and attach itself will depend on its weight, its ferritic iron content and how much it is interfered with by other objects so yes there is a relationship. Say that a particular object will attach itself to a particular magnet from a distance of 1 inch. Make the magnet twice as strong and it will move it from 1.414 inches (square root of 2 is 1.414)

Answer 2

A magnet attracts ferrous material by inducing an opposite pole in it. Using this concept, you can compute the force between two unit poles using the inverse-square law. Then given a piece of scrap of weight Mg, you can compute the work to move it by a distance S ( = F x S). Using this knowledge, you can back-calculate how much of amperage you need in your electromagnet to do a quanta of work.

Regarding the question by one of the answerers, an electromagnet regains its magnetism by virtue of the current flowing thru the coils. You can whallop it or heat it: this will only impact the "residual magnetism". But on turning on the current int he coils of the electromagnet, you will have the rated strength again.

Answer 3

hey i have a related question: i was taught that if you strike a magnet against a hard object, it loses its magnetism. if this is true, how do those magnets in junkyards work after being struck so much by cars being pulled up forcefully against it?

Answer 4

See http://en.wikipedia.org/wiki/Magnet