If you have kids, then you are probably familiar with this toy. Here's a quick description: A Magna Doodle is a drawing toy. It has a white screen and a "pen" that allows you to draw on the screen. As you draw, a very nice, dark black line forms within the white screen (this is weird and amazing to see in action -- check it out next time you pass a toy store). There is a slider at the bottom of a Magna Doodle, and by sliding it back and forth once or twice you erase the screen instantly and completely (also amazing).
Little kids love Magna Doodle, I think, because the drawn line is very bold. However, no pressure on the pen is required to create the line -- a light touch draws the same line as pressing hard does (unlike crayons). Parents love Magna Doodle because the pen contains neither ink nor paint to spill. The tip of the pen is a blunt piece of metal, so if the artist tries to write on a wall, nothing happens.
So how does a Magna Doodle work? There are four basic parts:
- There are two sheets of plastic, laid one on top of the other. The top one is translucent and forms the surface that the pen touches when drawing.
- Between these two sheets is a honeycomb lattice that acts as a separator. The lattice is visible when you look at the screen. It keeps the two sheets spaced apart at a uniform thickness and also divides the interior between the sheets into cells.
- In the cells between the sheets, there is an opaque white liquid (think of thick milk).
- Mixed with the liquid are very fine black magnetic particles of iron oxide.
When you apply a small magnet -- the blunt metal tip of the pen -- to the front screen, it draws the black magnetic particles through the liquid to the surface, and they become visible. They don't sink back into the liquid because of the thickness of the liquid, and because the particles and liquid are matched to have the same density. To erase the screen, the slider moves a long magnet across the back of the screen. This magnet drags the magnetic particles toward the back screen, and the white liquid covers them!
These links will help you learn more: