Electricity Chapter 13

Section 1

Electric Charge

Positive and Negative Charge

• There are two types of electric chargeo Protons have positive electric chargeo Electrons have negative electric chargeo What happens if an atom has an equal number of protons and

electrons? No net electrical charge Electrically neutral

o Do neutrons have an electric charge? No...neutrons are uncharged particles

• The strength of the attraction between electrons and the nucleus can vary between different types of atoms and molecules

• For Exampleo Electrons are more attracted to atoms in the soles of your shoes than

the atom in carpeto Electrons will transfer from the carpet to your shoes

What is the charge of the carpet now? Positive

o What is the charge of the soles of your shoes? Negative

o An accumulation of excess electric charge is called STATIC ELECTRICITY

Transferring Charge

When an object becomes charged Electrons usually moved from one object to another Charge cannot be created or destroyed Charge is transferred The Law of Conservation of Charge

Charge cannot be created or destroyed, but can be transferred from object to object

Conservation of Charge

The forces that exist between charges are dependent on two things The type of charge

Like charges repel Opposite charges attract

The distance between charges Force decreases as objects move apart

What do you think causes clothes in your dryer to be attracted to one another? Some clothes gain electrons (negatively charged) Some clothes lose electrons (positively charged) Clothes of opposite charge stick together

Charges Exert Forces

An electric field surrounds every electric charge The field exerts a force causing other electric charges to be repelled or

attracted Any charge in the field will be pushed or pulled Electric fields are represented by arrows that show how the field would

make a positive charge behave

Electric Fields

Remember…all objects are attracted on one another by gravitational forces

Electric forces are much stronger The electric forces between electrons and protons are what keep atoms

together

The Strength of Electric Forces

A material in which electrons are able to move easily is a conductor What type of material make the best conductors?

Metals A material in which electrons are not able to move easily is an insulator

Can you think of some examples? Wood, plastic

Thermal insulators and conductors are not always electrical conductors Can you think of a thermal conductor that is also an electrical conductor?

Metals Can you think of thermal conductor that is not an electrical conductor?

Glass

Conductors and Insulators

Rubbing objects together can result in a transfer of electrons One material has a positive charge and the other has negative charge This type of transfer is charging by contact

When a charge object comes near a neutral objects, the electrons of the neutral object will rearrange The neutral object becomes charges This type of transfer is charging by induction

Charging Objects

Lightning is the sudden discharge of charges built up in thunderclouds.

The collisions of atoms and molecules as they move through air cause air to emit light.

Lightning also produces powerful sound waves due to the large amount of heat that causes the surround air to expand rapidly and produce thunder.

To protect objects from being stuck by lighting, they are often “grounded” to Earth. Grounding provides a path for lightning to travel to the ground.

How It Works: Lightning

Lightning and Thunder

Electric charge can be detected using an electroscope

Detecting Electric Charge