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7.1 – Static Charge. OVERVIEW. Ancient Greece: when certain objects were rubbed (ex. amber) with wool or fur, they would attract lint and dust “STATIC” : stationary or not moving Static Charge (or static electricity): electric charges that can be collected and held in 1 place.

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overview
OVERVIEW
  • Ancient Greece: when certain objects were rubbed (ex. amber) with wool or fur, they would attract lint and dust
  • “STATIC”: stationary or not moving

Static Charge(or static electricity): electric charges that can be collected and held in 1 place

early theories of electricity
EARLY THEORIES OF ELECTRICITY
  • Hypothesized that there were 2 “electricities”
    • Rubbing materials like amber produces one
    • Rubbing materials like glass produces the other
  • Benjamin Franklin: hypothesized only 1 kind of “electrical fluid”
slide5

Performed experiments that caused a build-up of this electrical fluid

    • Called the build-up of fluid “positive” or “+”
    • Called the shortage of electrical fluid “negative” or “-”
  • Scientists still uses plus and minus to refer to electrical charge,

but the meaning is

NOT the same as

Franklin’s

review
REVIEW
  • All matter is made up of tiny particles called...ATOMS
  • Nucleus: the centre of the atom
    • Contains protons and neutrons
  • Neutrons: no charge
  • Protons: positive charge
  • Electrons: negative charge
in a solid material
In a solid material...
  • + nucleus vibrates but remains in the centre of the atom
  • - electrons move around the energy shells outside the nucleus

Result: ALL solid materials are charged by the transfer of electrons!

slide10
IONS
  • Ion: a charged atom
  • Electron(s) removed...
    • Because a negative charge is removed the atom has more positive than negative charges
    • More protons than electrons = + overall charge
slide11

Electron(s) added...

    • Because a negative charge is addedthe atom has more negativethan positivecharges
    • More electronsthan protons= -overall charge
summary
SUMMARY
  • The movement, or transfer, of electrons from 1 atom to another changes the atom’s charge
  • When an atom loses electrons, it becomes positive
  • When an atom gains electrons, it becomes negative
friction and elelctron transfer
FRICTION and ELELCTRON TRANSFER
  • Friction: occurs when 2 objects rub against each other
    • Results in 1 object losing electrons and 1 object gaining electrons

See Figure 7.3 in Textbook!

insulators and conductors
INSULATORS and CONDUCTORS

Think about this!

When you rub one end of a neutral plastic rob with a paper towel, the end you rub would become charged. The other end would remain neutral!

The electrons you

added to the neutral

plastic by friction will

stay in one place

slide15

Insulators: materials that do not allow charges to move easily

    • Electrons removed from one location on an insulator are NOT replaced by electrons from another location
    • EX.: glass, plastics, ceramics and dry wood
  • Conductors: materials that allow electrons to travel freely
    • Electrons from a charged items will spread evenly throughout a conductor
    • EX.: Metals (copper and aluminum)
slide16

Metals are good conductors because their atoms possess at least one easily transferable electron

  • Only insulators can retain a static charge
    • Static electricity is charge that is held very nearly fixed in one place
  • Conductors allow charge to flow
measuring charge
MEASURING CHARGE
  • Neutral objects:

# of electrons = # of protons

    • Smallest negative charge it can possess is -1 (gain 1 electron)
    • Smallest positive charge it can possess is +1 (lose 1 electron)
slide19

Coulomb (C): unit of electrical charge

  • 1 C of charge equals the addition or removal of
    • Lightning Bolt = 5C to 25C
    • Penny = 1 million coulombs of negative charge
      • Doesn’t give you a massive static shock because it also has about 1 million C of positive energy  NEUTRAL
generating static charge
GENERATING STATIC CHARGE
  • Charging an object by friction happens in everyday life
    • Static electricity in the clouds produces lightning (friction between hot air rising rapidly through cloud banks)
  • Scientists studying static charges need a special device that can produce large amounts of static charge in a laboratory
van de graaff generator
VAN de GRAAFF GENERATOR
  • Uses friction to produce a large static charge on a metal dome

Mechanics:

  • A moving belt produces a static charge at the base of the generator
  • The belt carries the charge to the top where it collects on the dome
applications of static electricity
Applications of Static Electricity
  • Many valuable uses in technology
    • Plastic sandwich wrap clings because of static electricity
    • Used to decrease air pollution
      • Devices in chimneys use static charge to remove small particles of smoke/dust from the air
    • Air ionizers
      • Remove electron particles from the air
    • Painting cars
      • Paint is given an electrical charge then sprayed on the car’s body (charged particles will stick to the metal)
dangers of static electricity
Dangers of Static Electricity
  • Fuel trucks must get rid of all static charge before they start pumping fuel
    • Attach a cable (conductor) to the truck that will transfer excess charge to the ground
      • GROUNDING: allowing charge to flow into the Earth’s surface (the Earth is large enough to accept charge without becoming charged)
      • Lightning strikes
      • Lightning rods are placed on top of buildings
      • The charge will pass through the rod to the ground instead of through the building