15.1. Static Electricity http://www.ck12.org
- Rub your hand against animal fur (ex. pet a cat) in dry weather, as inFigure15.1. Your cat may get an
unwelcome electric shock! - Use a plastic comb on your hair in a dark room and you may see electric sparks.
- Rub an inflated balloon against your shirt and then place it against a wall in your home. The balloon will
“stick” to the wall. - Plastic shrink wrap from the casing of a CD or DVD sticks to your hands after you open it.
- In cold or dry weather, you may get a painful shock when you reach for a doorknob after walking on a carpet.
FIGURE 15.1
Warning: On dry days your cat may take
issue with being petted.The intrinsic property of objects that helps describe all these and many other phenomena is known aselectric
charge. Electric charge is a fundamental property of matter, because every atom is composed of bothpositive
chargeandnegative charge. If enough positive and negative charges attract one another, an electric discharge
may occur. In an electric discharge, negative charge moves rapidly to an area of excessive positive charge and the
separate charge distributions neutralize. We will describe below how the properties of electric charges.
Static Electricity
An imbalance of one kind of charge is calledstatic electricity, and it can be caused by friction between two materials
or simply placing two objects in contact. If enough static electricity builds up, then it can discharge, resulting in a
shock or spark as the electric charge jumps to another object.
The American statesman and scientist Benjamin Franklin (1706-1790) assigned the termspositiveandnegativeto
the two different kinds of electrical charges. We will describe a demonstration below which aids in substantiating
the Law of Charges, which states that opposite charges attract, but like charges repel.
Franklin correctly believed that during an electrostatic interaction between two objects, an apparent increase of one
form of charge (say, positive charge) on one of the objects meant there must be an apparent increase of the other
form of charge (negative charge) on the other object. The number of both positive and negative charges remained
the same, but their distribution was altered. Today, we call this principle the law ofconservation of electric charge
and state it as:
The total charge remains constant in a closed system.