For the Love of Physics: From the End of the Rainbow to the Edge of Time - a Journey Through the Wonders of Physics by Walter Lewin

Author:Walter Lewin
Language: eng
Format: mobi
Tags: Science, Science & Technology, General, Astrophysics, Biography & Autobiography, Essays, Physics
ISBN: 9781451607130
Publisher: Simon and Schuster
Published: 2012-02-07T21:24:57+00:00

CHAPTER 8

The Mysteries of Magnetism

For most of us magnets are just fun, partly because they exert forces that we can feel and play with, and at the same time those forces are completely invisible. When we bring two magnets close together, they will either attract or repel each other, much as electrically charged objects do. Most of us have a sense that magnetism is deeply connected to electricity—nearly everyone interested in science knows the word electromagnetic, for instance—but by the same token we can’t exactly explain why or how they’re related. It’s a huge subject, and I spend an entire introductory course on it, so we’re just going to scratch the surface here. Even so, the physics of magnetism can lead us pretty quickly to some eye-popping effects and profound understandings.

Wonders of Magnetic Fields

If you take a magnet and put it in front of an older, pre-flat-screen television when it’s turned on, you’ll see some very cool patterns and colors across the screen. In the days before liquid crystal display (LCD) or plasma flat screens, beams of electrons shooting from the back of the TV toward the screen activated the colors, effectively painting the image on the screen. When you take a strong magnet to one of these screens, as I do in class, it will make almost psychedelic patterns. These are so compelling that even four-and five-year-olds love them. (You can easily find images of these patterns online.)

In fact, children seem to discover this on their own all the time. Anxious parents are all over the web, pleading for help in restoring their TVs after their children have run refrigerator magnets across the screens. Fortunately, most TVs come with a degaussing device that demagnetizes screens, and usually the problem goes away after a few days or a few weeks. But if it doesn’t, you’ll need a technician to fix the problem. So I don’t recommend you put a magnet near your home TV screen (or computer monitor), unless it’s an ancient TV or monitor that you don’t care about. Then you might have some fun. The world-famous Korean artist Nam June Paik has created many works of art with video distortion in roughly the same way. In my class I turn on the TV and pick out a particularly awful program—commercials are great for this demonstration—and everyone loves the way the magnet completely distorts the picture.

Just as with electricity, magnetism’s history goes back to ancient times. More than two thousand years ago the Greeks, the Indians, and the Chinese apparently all knew that particular rocks—which became known as lodestones—attracted small pieces of iron (just as the Greeks had found that rubbed amber would collect bits of leaves). Nowadays we call that substance magnetite, a naturally occurring magnetic mineral, in fact the most magnetic naturally occurring material on Earth. Magnetite is a combination of iron and oxygen (Fe3O4) and so is known as an iron oxide.

But there are lots of different kinds of magnets, not only magnetite. Iron has played

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