5.64. Static Electricity and Static Discharge http://www.ck12.org
Q:You’re more likely to get a shock in the winter when the air is very dry. Can you explain why?
A:When the air is very dry, electric charges are more likely to build up objects because they cannot travel easily
through the dry air. This makes a shock more likely when you touch another object.
Static Discharge
What happens when you have become negatively charged and your hand approaches the metal doorknocker? Your
negatively charged hand repels electrons in the metal, so the electrons move to the other side of the knocker. This
makes the side of the knocker closest to your hand positively charged. As your negatively charged hand gets very
close to the positively charged side of the metal, the air between your hand and the knocker also becomes electrically
charged. This allows electrons to suddenly flow from your hand to the knocker. The sudden flow of electrons is
static discharge. The discharge of electrons is the spark you see and the shock you feel. Watch the animation “John
Travoltage” at the following URL to see an example of static electricity and static discharge.
http://www.cabrillo.edu/~jmccullough/Physics/Electric_Forces_Fields.html
How Lightning Occurs
Another example of static discharge, but on a much larger scale, is lightning. You can see how it occurs in the
following diagram (Figure5.150) and animation as you read about it below.
http://micro.magnet.fsu.edu/electromag/java/lightning/index.html
FIGURE 5.150
During a rainstorm, clouds develop regions of positive and negative charge due to the movement of air molecules,
water drops, and ice particles. The negative charges are concentrated at the base of the clouds, and the positive
charges are concentrated at the top. The negative charges repel electrons on the ground beneath them, so the ground
below the clouds becomes positively charged. At first, the atmosphere prevents electrons from flowing away from
areas of negative charge and toward areas of positive charge. As more charges build up, however, the air between
the oppositely charged areas also becomes charged. When this happens, static electricity is discharged as bolts of
lightning.
At the URL below, you can watch an awesome slow-motion lightning strike. Be sure to wait for the real-time