9. Static electricity Flashcards
what kind of materials are electrical conductors?
silver, copper, alumininum, steel (delocalised electrons)
what kind of materials are insulators?
rubber, plastic, glass, wood
but can conduct a bit of static electricity, just not a flow of charge
what happens when a cloth and rod are rubbed together?
- initially neutral
- force of friction causes electrons to move
if the cloth transfers some electrons to the rod, what charge will the objects now have?
cloth: more protons -> positive
rod: more electrons -> negative
what charge does polythene get when charged with cloth?
negative
why are charges evenly distributed in a conductor?
electrons are repelled by other electrons, and these are attracted to protons
is it possible to move positive charges?
no
is it possible to move negative charges?
yes! electrons are not within nucleus
charging via induction
What happens if you bring a negatively charged rod near a piece of paper (neutral)?
- rod approaches paper, electrons in paper are repelled away from rod
- makes one side of paper negative and other positive
- positive side is closer to rod
- resultant force = attractive as opposite charges are closer
- paper sticks to rod
works the same if rod is positive -> electrons attracted to one side
charging by contact
How can a neutral object become charged by touching a charged object?
electrons flow onto (if object positively charged) or off of object (if negatively charged, as the elctrons repel each other and move away from each other)
what is earthing?
- charge on object is neutralised by transfer of electrons
why would electrons try to flow off of a negatively charged object?
they are repelled
why would electrons try to flow onto a positively charged object?
they are attracted
what is the purpose of a photocopier?
to print copies of an image/document
how does a photocopier work?
1. what is done to the drum before toner is added?
- image of document is projected on to positively charged drum
- drum loses charge in light areas and keeps positive charge in dark areas (light areas conduct electricity)
- negatively charged toner sticks to where there is a positive charge on drum
- transferred onto paper
how do inkjet printers work?
- ink droplets positively charged via charging electrodes
- pass between oppositely charged plates
- computer controls plate voltage
- droplets attracted towards negatively charged plate + repelled from positive one (the deflection can be changed by altering strength of plate charges)
- direction changed by changing the charge of the plates
how does electrostatic paint sprayer work?
- paint droplets given charge by paint sprayer so repel each other-> fine mist and covers large area
- oppositely charge car
- less waste, more even coverage
how does a dust precipitator work?
- reduces pollution
- dust becomes charged by passing thru negatively charged plates
- dust removed from air as attracted to positively charged plates
- dust removed from collecting plates as it is neutralised upon touching the plates, falls into dust collection
how is lightning made?
- droplets + ice crystals rub against each other in cloud during storm, creates static electrical charge
- clouds have positive and negative side
- negative side is at the bottom -> when there is enough charge in the cloud it is released via lightning bolt, which is goes to anything oppositely charged (eg lightning conductor, positively charged, earths it)
why is refuelling airplane potentially dangerous?
- build up of static charge : friction between fuel and pipe, fuel gains charge -> could spark and fuel could ignite and explode (also friction with air whilst flying can cause a charge)
- explosion prevented by fuel tank being connected to earth w conductor
- carriers charge through to earth to reduce sparking risk
