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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
EARLY THEORIES OF ELECTRICITY
Hypothesized that there were 2 “electricities” Rubbing materials like amber produces oneRubbing materials like glass produces the
other
Benjamin Franklin: hypothesized only 1 kind of “electrical fluid”
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
PARTICLES!
Modern theories about electricity are based on.....
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
If the # of protons and electrons is equal, the atom is uncharged or neutral!
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!
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
Electron(s) added...Because a negative charge is added the
atom has more negative than positive charges
More electrons than protons = - overall charge
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: 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
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
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 conductorEX.: Metals (copper and aluminum)
Metals are good conductors because their atoms possess at least one easily transferable electron
Only insulators can retain a static chargeStatic electricity is charge that is held very
nearly fixed in one place Conductors allow charge to flow
MEASURING CHARGE
Neutral objects:
# of electrons = # of protonsSmallest negative charge it can possess is -1
(gain 1 electron)Smallest positive charge it can possess is +1
(lose 1 electron)
Coulomb (C): unit of electrical charge 1 C of charge equals the addition or
removal of Lightning Bolt = 5C to 25CPenny = 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
Charging an object by friction happens in everyday lifeStatic 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
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
Many valuable uses in technologyPlastic sandwich wrap clings because of static
electricityUsed 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
Fuel trucks must get rid of all static charge before they start pumping fuelAttach 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