This topic accounts for approximately 6% of your exam marks.
stable
Low
Stable6%
Charging by friction, electric fields and uses/dangers of static electricity tested as shorter questions.
Conductors
A conductor is a material that lets electric charge flow through it readily
Familiar conductors are almost all metals:
silver, copper, gold (excellent conductors)
aluminium, steel, iron (good conductors)
Why metals conduct so well:
inside a metal, the outermost electrons of each atom are delocalised, so they are no longer tied to one particular atom and drift freely through the lattice of fixed positive ions
an electric field set up across the metal makes these free electrons drift along the wire, and a current is simply the rate at which they move
Insulators
An insulator is a material with no free electrons: every electron is bound to a particular atom, so charge cannot drift through the bulk of the material
Insulators do not conduct current, but charge can still be deposited on their surface by rubbing, and that surface charge is what static electricity is all about
Some insulators (wood, paper, hair) can build up a noticeable surface charge that leaks slowly into the surroundings; truly dry, pristine plastics can hold a charge for hours
Why the distinction matters for static electricity
Excess charge on a spreads itself evenly across the surface and flows away to earth almost instantly if any conducting path exists
Excess charge on an stays put on the surface where it was deposited; it cannot leave by flowing through the bulk
Static-electricity experiments therefore use insulating rods (polythene, acetate, perspex) so that the charge built up by friction stays on the rod long enough to test