UNIT 3

A HAIR RAISING EXPERIENCE

Electrons and the nucleus

• Electrons in atoms are attracted to the

positive nucleus

– But they can be pulled away from the nucleus

3+ 3+ +

3 electrons and 3 protons

Charge= neutral 2 electrons and 3 protons

Charge = 1+

1 electron

Charge = 1-

Science 9: Chapter 7- Key Words to Know

Acetate

Action-at-a-distance

force

Charging by conduction

Charging by induction

Conductors

Contact forces

Coulomb

Electric force

Electrons

Force

Grounding

Insulators

Laws of static charge

Static charge

Van de Graaff generator

UNIT 3: CHARACTERISTICS OF ELECTRICITY

CHAPTER 7: STATIC CHARGE

In this chapter you will:

•Explain, with illustrations, the transfer of static charges in various materials

•Describe types of static charge

•State the 3 laws of static charge

•Explain what factors affect the force between charges

Lab: Static Stations

• With your lab partner, you will move

through each of the 4 lab stations

• You will have 10 minutes at each station to

experiment and answer the questions for

each station

STATIC ELECTRICITY = Electrical

charge that is built up in one place

• Static charge is often encountered in

everyday life when objects rub against

one another and transfer charge,

(friction!)

Positive and Negative Charges

• Solid materials are charged due to the

movement of electrons - when electrons are

gained, the object becomes negative. When

electrons are lost, the object becomes

positive.

• Electrons are most often transferred through

friction (when objects rub against each other).

ELECTRIC CHARGE: Remember:

OPPOSITES ATTRACT, LIKE CHARGES

REPEL

Electric Discharge:

• the removal of electric charge from an

object

• Ex. Lightening

“shocks”

Travoltage…

• http://phet.colora

do.edu/en/simula

tion/travoltage

Lighting

_ _ - _ _ - _ - _ _ _ -

+ ++ + + + + + +

+ ++ +

+ + + + +

+ ++ +

+ + +

Lighting

_ _ - _ _

_ _ -

+ ++ + + + + + +

+ ++ +

+ + + + +

+ ++ +

+ + +

- _ - _

The coulomb (C):

• The unit of electric charge

• Takes the addition or removal of 6.25 x

1018 electrons to produce 1 C of charge

Insulators and Conductors

Materials that do not allow charges to move easily are

called electrical insulators

Electrons removed from one location

are not replaced by electrons from

another location

Only insulators are good at retaining static charge

Materials that allow electrons to travel freely are called

electrical conductors

Electrons spread easily

over the entire rod

. Decreasing Air Pollution

Collecting plates are

knocked to remove

the smoke particles.

Applications of Static Electricity - p 253 You need to be able to explain how static electricity can be useful

Questions

A. Name 2 places where this method of decreasing air pollution would be seen

i)

ii)

B. Explain how static electricity is useful for painting automobiles

C. State one other use for static electricity

Smoke

particles

pick up a

negative

charge

Smoke

particles are

attracted to the

collecting

plates

Negatively

charged metal

grid

/10 Name:

Dangers of Electricity p 254

Use the back of this worksheet to write your own notes on the Dangers of Electricity

Generating Static Charge

• Van de Graff generators (VDG)

use friction to produce large

amounts of static charge.

• As a rapidly moving belt moves

over metal rollers,

contact between the two results

in a transfer of charge to the belt

• A moving belt produces static

charge on a metal dome -

See page 253

Electric force

• Force: a push or a pull

• Electric force: push or pull between

charged objects

Laws of Electric Charges

• http://phet.color

ado.edu/en/sim

ulation/balloons

Laws of Static Charges

1. Opposite charges attract

+ -

Laws of Static Charges

2. Like charges repel

+ + - -

Laws of Static Charges

3. Charged objects can attract neutral

objects

+ - - - -

- -

+ +

+

+ -

- -

- -

+ + + + +

+

Charging by friction H

um

an s

kin

Leath

er

Rabbit's

fur

Gla

ss

Hum

an h

air

Nylo

n

Wool

Lead

Cat's

fur

Silk

Paper

(Sm

all

positiv

e c

harg

e)

Cotton (

No c

harg

e)

0

Ste

el (N

o c

harg

e)

Wood (

Sm

all

negative c

harg

e)

Lucite

Am

ber

Sealin

g w

ax

Acry

lic

Poly

sty

rene

Rubber

ballo

on

Resin

s

Hard

rubber

Nic

kel, C

opper

Sulfur

Bra

ss, S

ilver

Gold

, P

latinum

Aceta

te,

Rayon

Synth

etic r

ubber

Poly

este

r

Sty

rene (

Sty

rofo

am

)

Sara

n w

rap

Ebonite

Materials that

lose electrons

Materials that

gain electrons

Charging Objects

Charging By Conduction • Charging through direct contact. Extra electrons

will move to a location where there is less of them.

• This transfer of charge may be accomplished by FRICTION, (rubbing objects together)

Charging By Induction • Bringing a charged object nearby a neutral object will

cause a temporary charge separation in another object

+ - + - +

- + - + -

+ - + - +

- + - + -

- - - -

- - - -

- - - -

Charged object neutral object an induced charge

Charging by conduction

• Charging a neutral object by touching a charged object to it.

• Electrons are transferred.

+

Charging by induction

• Charging a neutral object bringing a charged object near it.

• No electrons are transferred.

+ + + +

Charging Objects by conduction and induction