18.1 Static electricity and charge: conservation of charge

Learning objectives

By the end of this section, you will be able to:

• Define electric charge, and describe how the two types of charge interact.
• Describe three common situations that generate static electricity.
• State the law of conservation of charge.

The information presented in this section supports the following AP® learning objectives and science practices:

• 1.B.1.1 The student is able to make claims about natural phenomena based on conservation of electric charge. (S.P. 6.4)
• 1.B.1.2 The student is able to make predictions, using the conservation of electric charge, about the sign and relative quantity of net charge of objects or systems after various charging processes, including conservation of charge in simple circuits. (S.P. 6.4, 7.2)
• 1.B.2.1 The student is able to construct an explanation of the two-charge model of electric charge based on evidence produced through scientific practices. (S.P. 6.4)
• 1.B.3.1 The student is able to challenge the claim that an electric charge smaller than the elementary charge has been isolated. (S.P. 1.5, 6.1, 7.2)
• 5.A.2.1 The student is able to define open and closed systems for everyday situations and apply conservation concepts for energy, charge, and linear momentum to those situations. (S.P. 6.4, 7.2)
• 5.C.2.1 The student is able to predict electric charges on objects within a system by application of the principle of charge conservation within a system. (S.P. 6.4)
• 5.C.2.2 The student is able to design a plan to collect data on the electrical charging of objects and electric charge induction on neutral objects and qualitatively analyze that data. (S.P. 4.2, 5.1)
• 5.C.2.3 The student is able to justify the selection of data relevant to an investigation of the electrical charging of objects and electric charge induction on neutral objects. (S.P. 4.1)

What makes plastic wrap cling? Static electricity. Not only are applications of static electricity common these days, its existence has been known since ancient times. The first record of its effects dates to ancient Greeks who noted more than 500 years B.C. that polishing amber temporarily enabled it to attract bits of straw (see [link] ). The very word electric derives from the Greek word for amber ( electron ).

Many of the characteristics of static electricity can be explored by rubbing things together. Rubbing creates the spark you get from walking across a wool carpet, for example. Static cling generated in a clothes dryer and the attraction of straw to recently polished amber also result from rubbing. Similarly, lightning results from air movements under certain weather conditions. You can also rub a balloon on your hair, and the static electricity created can then make the balloon cling to a wall. We also have to be cautious of static electricity, especially in dry climates. When we pump gasoline, we are warned to discharge ourselves (after sliding across the seat) on a metal surface before grabbing the gas nozzle. Attendants in hospital operating rooms must wear booties with aluminum foil on the bottoms to avoid creating sparks which may ignite the oxygen being used.