Chapter 9 Static Electricity

9.1 Types of Static Charge

• A static charge is an electrical

charge

• It is eventually discharged or lost

• There are two types of charges

– Positive (+) electrons removed

– Negative (-) electrons added

Law of Electric Charges

• The law of electric charges states

that like charges repel and unlike

charges attract

• Some materials are more likely than

others to gain or lose electrons.

Substances are ranked on the

electrostatic series. If two

substances are rubbed together,

electrons are transferred. One

object becomes negatively charged,

one object becomes positively

charged.

• A neutral object is attracted to

charged objects due to movement

of electrons. Neutral objects get an

induced charge separation.

Assignment

• P. 278 #1-7, 11-14

9.2 Charging by Friction,

Conduction and Induction

Friction

• Charging by friction happens by two

objects rubbing together

• Eg. Clothes in a dryer

Conduction

• Charging by conduction happens

when objects touch and charge is

transferred

• Eg. Touching a door and getting a

shock

Induction

• Charging by induction occurs when

an object is charged without

touching or making direct contact

• Eg. Dust attracted to TV screen

Assignment

• P. 281 #4-6, 8-10

9.3 Insulators and Conductors

Insulators

• An insulator is a substance in which

electrons are not free to move

• Eg. Plastic, wood, glass, wool

Conductors

• A conductor allows electrons to

move freely

• Eg. metals

• Generally static charge can build up

on insulators, but not conductors

Electroscope

Electroscope

• Metal leaves move apart when

there is a charge separation

• Electroscope is grounded when top

is touched

Assignment

• P. 284 #2-4, 6-8, 10

9.4 Electric Force

Van De Graaf Generator

• A Van De Graaf

generator is a

device which

separates large

quantities of electric

charge

Electric Force

• An electric force is a force that exists between static charges.

• It can be a push or pull

• The strength of the force increase with increasing electric charge

• The strength of the force decreases with increasing distance

• The size of the force is measured in coulombs

Assignment

• P. 287 #1, 5, 7-9

9.5 Applications of Static

Electricity

Lightning

Lightning

• Electrons are transferred from rising water to falling water

• Negative charges at bottom, positive charges at top

• Electrons at the surface of the earth are repelled and earth gets a strong positive charge

• Moving electrons fall to earth

• The exited gas produces light and expanding gases produce the sound

Laser Printers

Laser Printers

• Laser device emits light, reflected on to

drum

• Drum is given positive charge

• Laser causes negative charge on drum

in shape of letters and images

• Drum rolled in toner (positive charge)

• Toner sticks to negative areas of drum

• Paper (negative) rolls under drum

• Fuser heats toner, melts onto page

Fabric Softener

• Clothes rub against each other

causing static charges

• Fabric sheets contain a chemical

that is attracted to negatively

charged clothes

• Chemical is slightly oily, coats

clothes

• Reduces friction

Electrostatic Precipitators

Electrostatic Precipitators

• Burning coal produces pollutants and ash

• Electrostatic precipitators are used to remove ash (also wood dust)

• Negatively charged plates have ash pass by them

• Ash acquires a negative charge

• Attracted to positively charged plates

• Ash is shaken or scraped off plate

Assignment

• P. 290 #1-3, 5-6, 10

Review Assignment

• P. 298 #1-9, 11, 14