Chapter 20, Section 1Electric Charge and Static Electricity

Wednesday, January 6, 2010

Pages 643 -- 670

Objectives

Describe the interaction of like and unlike electric charges.

Define and describe static electricity and state how it differs from electric current.

Describe lightning and other forms of static discharge.

Vocabulary Words

Electric field Static electricity Conduction

Induction Conservation of

charge Static discharge Electroscope

Types of Electric Charge

Charged parts of atoms are electrons and protons.

Proton = positive (+)Electrons = negative (-)

Interaction Between Charges

Charges that are the same repel each other.

Charges that are different attract each other.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Electric Fields

An electric field surrounds the charge -- it extends outward from every charged particle. It is either pushed (if

the 2 charges are the same) or pulled (if the two charges are different).

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Electric Fields Around Single Charges

Electric field lines are drawn with arrows to show the direction of the force on a positive charge.

The EF is strongest where the lines are closest together (near the charged particle).

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Electric Fields Around Multiple Charges

The EF is altered when there are two or more charges.

The EF due to the individual charges combine.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Static Charge

Electrons are carried up a rubber belt and transferred to the metal sphere.

The charge built up on the sphere is enough to send a spark several meters through the air.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Van de Graaf generator

Charged Objects

The buildup of charges on an object is called static electricity. Charges build up but they DO NOT flow.

Atoms in insulators hold their electrons tightly.

Atoms in conductors hold some of their electrons loosely -- able to move freely.

Transferring Charge

There are 3 methods by which charges are transferred: Friction -- transfer of electrons from one object

to another by rubbing. Conduction -- transfer of electrons from one

object to another by direction contact. Induction -- movement of electrons to one part

of an object caused by the electric field of another object.

Conservation of Charge

Charges are not created.Charges are not destroyed.If one object gives up electrons, another

object gains those electrons. Electrons are only transferred from one location

to another.

Static Discharge

Defined as the loss of static electricity as electric charges move off an object. When a negatively charged object and a

positively charged object are brought together, electrons move until both objects have the same charge.

Electroscope

This special instrument can detect electric charge.

QuickTime™ and aTIFF (Uncompressed) decompressor

are needed to see this picture.

Homework

Workbook 20.1 (due 1/8)Worksheet 20.1 (due 1/7)Vocabulary quiz 20.1 (due 1/8)