Chapter Twenty: Electric Circuits 20.1 Charge 20.2 Electric Circuits 20.3 Current and Voltage 20.4 Resistance and Ohm’s Law

20.1 Electric charge Electric 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 Charge Virtually 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 forces Whether 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 forces The 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 forces Electric 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 forces Lightning 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.