Static electricity

 

I’m a little nervous as I word-process this column about static electricity, because every computer owner knows (and usually learned the hard way), that static electricity is a Bad Thing.

Static electricity, however, has been around longer than computers:  like, forever.  The first time anybody noticed, though, was around 600 B.C., when the Greeks found that rubbing a piece of amber with a piece of fur gives the amber the ability to attract feathers and bits of other materials.  This was thought to be unique to amber, for which the Greek word was “elektron,” so this property became known as “electricity.”

In the 16th century, William Gilbert proved that other substances are also “electric,” and that there are two kinds of electricity.  Rubbing amber with fur produced “resinous electricity,” while rubbing glass with silk produced “vitreous electricity.”  Objects with different electricity attracted each other and objects with the same kind repelled.

In 1747, Benjamin Franklin in America and William Watson in England realized that all objects possess an electrical “fluid” which can be transferred by friction.  Franklin called objects with more of the fluid “positive,” while those lacking the fluid were “negative,” the first use of those terms for electrical charges (although Franklin thought charge flowed from positive to negative, and it actually flows the other way).

Franklin thought lightning was a form of electrical discharge, and tested his idea by flying a metal-tipped kite in a thunderstorm in 1752.  He attached a metal key to the wet hemp kite-line, held on to a non-conducting silk string, and during the storm, drew sparks from the key with his knuckles.  (He also almost vacated his prominent place in the history of the United States:  the next two people who tried this were killed.)

Today we know that all objects are made up of atoms.  Each atom has a nucleus made up of positively charged protons and chargeless neutrons.  Around the nucleus orbit negatively charged electrons.  Normally, there are just as many electrons as protons, giving a net charge of zero.

However, friction can dislodge some electrons.  Objects that lose electrons become positively charged and objects that gain electrons become negatively charged.

Shuffle your feet across a carpet, then touch a metal doorknob.  Your body picks up electrons from the carpet, gaining a powerful negative charge.  When you approach the doorknob, your negative charge repels the negatively charged electrons near the knob’s surface.  They retreat, leaving the surface positively charged.  This attracts the extra electrons in your body, which leap across the intervening distance.

Or try rubbing a balloon in your hair and sticking it to the wall (the balloon, that is, not your hair).  The balloon’s negative charge pushes away the negatively charged electrons in the surface of the wall, resulting in a positively charged surface that then attracts the balloon.

Sparks result from air’s resistance to having electrons shoved through it:  it gets white-hot.  The “crack!” is miniature thunder:  the white-hot air expands, creating a partial vacuum along the spark’s path.  When surrounding air rushes back into that vacuum, the molecules crash together with an audible snap.

Under ideal conditions, you can accumulate a charge of more than 20,000 volts just by rubbing your shoes on the carpet.  Although it can be painful, it’s not harmful, because low current is involved.

“Ideal conditions” might mean it’s a cold mid-winter’s day, because cold air can’t hold as much moisture as warm air.  Moisture reduces improves electrical conductivity, allowing electrical charges to bleed off before they reach noticeable levels.

Clothes build up static in dryers because of the different materials rubbing against each other.  Fabric softeners coat cloth with a thin layer of soapy chemical, which hampers the exchange of electrons, reducing static cling.

Although static electricity is mostly a nuisance, it does have some uses:  the “scrubbers” in many industrial smokestacks, for instance.  Most smoke particles are electrically charged, and can therefore be attracted to charged plates, then forced into a collector.  Televisions also use charged plates to deflect the beam of electrons that sweeps over the phosphorescent inside of the screen every few seconds, painting a constantly changing picture of Oprah.

Amazing!  A whole column on static electricity, and my computer remains “unzapped.”

Frankly, I’m shocked.

Permanent link to this article: https://edwardwillett.com/1993/12/static-electricity/

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