ELECTRIC CIRCUITS 20.1

Chapter Twenty: Electric Circuits

20.1 Charge20.2 Electric Circuits20.3 Current and Voltage20.4 Resistance and Ohm’s Law

Chapter 20.1 Learning Goals

Define static electricity and discuss its causes.

Explain what it means when an object is electrically charged.

Discuss the relationship between like and unlike charges.

Investigation 20C

Key Question:What is static electricity?

Electric Charge

20.1 Electric chargeElectric charge, like

mass, is also fundamental property of matter.

Inside atoms found in matter, attraction between positive and negative charges holds the atoms together.

20.1 ChargeVirtually all the matter

around you has electric charge because atoms are made of electrons and protons (and neutrons).

Because ordinary matter has zero net (total) charge, most matter acts as if there is no electric charge at all.

20.1 Electric and magnetic forcesWhether two charges

attract or repel depends on whether they have the same or opposite sign.

A positive charge attracts a negative charge and vice versa.

Two similar charges repel each other.

20.1 Electrical forcesThe unit of charge is the coulomb (C). The name was chosen in honor of

Charles Augustin de Coulomb (1736-1806), the French physicist who performed the first accurate measurements of the force between charges.

20.1 Electrical forcesElectric forces are incredibly strong.

A millimeter cube of carbon the size of a pencil point contains about 77 coulombs of positive and negative charge.

20.1 Electrical forcesLightning is caused by a

giant buildup of static charge.

The cloud, air, and ground can act like a giant circuit.

All the accumulated negative charges flow from the cloud to the ground, heating the air along the path (to as much as 20,000°C) so that it glows like a bright streak of light.