Foundations of Physical Science Unit 3: Electricity and Magnetism

Chapter 6: Electricity and Electric Circuits 6.1 What is a Circuit? 6.2 Charge

Learning Goals Build simple circuits. Trace circuit paths. Interpret the electric symbols for battery, bulb, wire, and switch. Draw a circuit diagram of a real circuit. Explain why electrical symbols and circuit diagrams are useful. Explain how a switch works. Identify open and closed circuits. Charge pieces of tape and observe their interactions with an electroscope. Identify electric charge as the property of matter responsible for electricity. List the two forms of electric charge. Describe the forces electric charges exert on each other. Describe how lightning forms.

Vocabulary circuit diagram closed circuit coulomb electric circuits electrically charged electric charge electrically neutral electroscope electrical symbols natural world negative charge open circuit positive charge static electricity versorium

What is a Circuit? Something that provides a path through which electricity travels Electricity: the flow of electric current in wires, motors, light bulbs, and other devices Electric current: flow through solid metal; can carry energy over great distances Can be powerful and dangerous!

Circuits Are All Around Us! Wiring that lights your house Nerves in your body Lightning, clouds, and the planet Earth Car battery, ignition switch, and starter Electric circuits are like water pipes and hoses, except electricity cannot flow if a wire is cut (but water can!) Switches turn circuits on and off

Circuit Diagrams Circuit are made up of wires, electrical parts (batteries, light bulbs, motors, or switches) Circuit diagrams are used as a shorthand method to describe a real circuit Resistor: an electrical component that uses energy (example: light bulbs)

Circuit Diagrams

Open and Closed Circuits Open circuit: a circuit with a switch turned to the off position of a circuit with any break in it Closed circuit: a circuit with the switch(es) turned to the on position, without any breaks in the wire. If attached to a light bulb, the light will be on! Short circuit: an accidental extra path for current to flow

Charge Electric charge is a fundamental property of matter. Flows through a circuit There are two types of charge: positive negative

Charge The terms positive and negative to describe the opposite kinds of charge were first used by Benjamin Franklin (1706-1790). In 1733, French scientist Charles DuFay had published a book describing how like charges repel and unlike charges attract.

Atoms Same number of electrons as protons Ion: a charged atom Positive ion: lost electrons Negative ion: gained electrons

Conservation of Charge No electrons are created or destroyed They are transferred from one material to another Charge is conserved

Example If you walk across a rug and scuff electrons from your feet, are you negatively or positively charged? You have fewer electrons and are thus positively charged (the rug is negatively charged)

The Coulomb The unit of electric charge (C) Named after Charles-Augustin de Coulomb, a French physicist

The Electroscope Tool used to measure charge in objects Versorium: the first electrical instrument The earliest version of today’s electroscope

Coulomb’s Law Electrical force has a pattern like gravitational force Discovered by Charles Coulomb in the 1700s Like charges: repelling force Unlike charges: attractive force

Coulomb's Law in Summary Newton’s law of gravitation for masses is similar to Coulomb's law for electrically-charged bodies The important difference: electrical forces may be either attractive or repulsive, whereas gravitational forces are only attractive