The Nature of Electricity

STATIC ELECTRICITY

• show that things can be electrified.

• understand fluid models of electricity. • describe the concept of an electric charge.

KEY WORDSElectrified Electrostatic Static

Positive charge Negative charge

Electrostatics:Study of static electricity – static means “at rest.”• electricity that is at a point, not moving.

Ancient Greece philosophers noted; Amber rubbed with fur attracted small bits of paper and dust.

Electric, electricity and electron come from the Greek term elektron - means amber.

Charles Dufay and Benjamin Franklin (1700s)

• Rubbing objects together caused them to repel or attract materials – charged.• Electric charge on an object came from a

transfer of invisible fluid from one object to another.

Dufay - two kinds of electric fluids.Franklin – one kind of fluid.

*Atoms (protons, neutrons, electrons) were not discovered yet.

first to use positive and negative to describe charges.

Two fluids• Equal amount – neutral

Two fluids• More blue – negative

Two fluids• More red – postive

Attracted objects • trading fluids

Just enough fluid.

TOO little fluid

TOO much fluid

• Static is a stationary electric charge built up on a material – usually temporary.

• Different materials can be electrified by contact.

• Charges give forces of attraction and repulsion.

• There exist two kinds of charge – (+) and (-)

• Like charges repel, unlike charges attract.

• Neutral object is attracted to both types of charges.

• Describe how friction can create an electrical charge on a material

• Describe conductors and insulators

KEY WORDSFriction Conductor Insulator

Triboelectric

Charges were described based on behaviour of objects - operational definition.

Positive charge – repels a glass rod that has been rubbed with silk.

(+) charge

Negative charge – repels a plastic straw rubbed with wool.

(-) charge

Static charge - result of charges transferred from one object to another by friction.

Atoms contain 3 subatomic particles:The dense center (nucleus) of the atom contains:

Neutron - a particle with no charge. Proton - a particle with a positive charge.

Electrons move around the nucleus. - negative electrical charge.

- same # of positive and negative charges = neutral.

Atoms: electrostatically neutral – same # p+ and e-.

Strong forces hold protons in nucleus – no move.Electrons are weakly held - easily removed.

Friction (rubbing) provides enough energy to cause electrons to transfer to new material.

Negative and positive static charges result from the addition or removal of electrons only.

Objects can exist in three states electrically:

1. Neutral: positive and negative charges on the object are balanced – net charge is zero.

2. Positive charge: object has lost negative charges (electrons) – net charge is positive.

3. Negative charge: object has gained negative charges (electrons) – net charge is negative.

Different materials have different strength of attraction for electrons.

The stronger one will take electrons away from weaker one and static charges build up.

Hair with comb:• plastic comb has stronger attraction to electrons,

so it removes some from hair.• Hair (+) charged, silk (-) charged.

Triboelectric charging – process of electron transfer by friction ('tribo' means 'to rub’)

Most Positive (+)Human Skin

+++  

 +

Rabbit FurGlass

Human HairNylonWoolSilk

Paper

Cotton  Wood

- 

- - -

AmberRubberNickelCopperSilver

PolyesterPlastic

Most Negative (-)

+

+

+

+

+++- -

-

--

-

- --

-

+

+

+

• Electrons can be made to move from one atom to another.

• Moving electrons creates a current of electricity.

Electricity is not a fluid, it is the movement of the charged particles between the objects... the two

objects are really exchanging electrons.

Insulators:• Do not allow an electrical charge to move around.• Electrons stay in one place until removed.

Rubber, plastic, cloth, glass, wood.

Conductors:• Electrons move easily through the material.• Electrical charge is spread out and weakened.

Most metals are good conductors.