# Induced magnetism

Both N and S poles exert an attractive force on non-magnetized iron. How does that square with just 2 kinds of poles?

### Differences between E and M

It is quite possible to give an object just one kind of charge.

But magnets always come as a package deal: if there's a N pole on one end of a magnet, there's bound to be a S pole on the other end. If you break a magnet in half...

A thing that has a north pole but no south pole is called a monopole, but such an object has never been found.

### Induced magnetism

Or if the other pole is brought close:

Now, if you take away the magnet the material is still *kinda* magnetized. There is some remnant magnetization. Notice that most of the little magnets have their dark ends pointing right.

Could mention here: Curie temperature

This is the basis for computer hard disk drives...

### Current going in circles

We examined the field around a coil of wire, where the current goes around in circles.

The field looks the same as the field around a magnet:

The modern picture is that all magnetism is caused by small currents--electrons running in circles around their atoms. Sorta like planets orbiting the sun.

### Magnetic recording

An electro-magnet moves about a surface coated with some magnetic material, and gives it a remnant magnet field point one way or the other (these are the '1's and '0's of binary coding).

### Static cling

A rubbed (statically charged) balloon sticks to a wall (which hasn't been rubbed!)

We understand this in terms of an induced charge [PhET]:

The positively charged nuclei of atoms cannot move--they are locked in bonds with their neighbors. But a few of an atom's electrons are free to move.

The electrons will move towards a positively charged object nearby, so the positive object is attracted towards the buildup of negative charge.

The electrons will move away from a negatively charged object, leaving behind a more positive region...which attracts the negative object.

So, either way, there's an attraction!