P11 | static electricity Flashcards
what is static charge?
an electric charge that cannot flow
how do insulators become electrically charged?
- rubbing two insulating materials together (e.g. balloon and cloth) creates friction
- which causes electrons to be transferred from one the materials to the other
balloon has an induced negative charge due to electrons from the cloth being transferred to the balloon
cloth has an induced positive charge due to loss of electrons
how do negatively charged balloons pick up paper?
- induced negative charge in the balloons repels the electrons in the paper
- this creates an induced positive side to the paper which is attracted to the balloon
how is lightning formed?
- water droplets and ice collide within clouds
- as they collide friction causes electrons to be removed from atoms and negative charge to accumulate at the base of the clouds (top of the cloud becomes positively charged)
- this causes positive charges to be induced on the ground
- an electric field/potential difference builds up between the cloud and the ground which ionises the air
- when the potential difference is large enough the electrons from the clouds are attracted to the positive charges on the ground
how do electrics shocks happen?
- friction from rubbing feet against the carpet causes a buildup of electrons on your clothes
- the charge is static (cannot flow) because clothes are an insulating material
- as you move near someone else, you induce a positive charge on them which creates an electric field
- charge jumps from you (negative) to them (positive)
- creating an electric shock
how does static charge build up on a car?
- air flow over car = friction
- charge builds up on car as rubber tyres (insulators) prevent change from flowing to the ground
how does earthing remove excess built-up charge from objects?
- a conductor (metal wire) is connected between a lightning rod and a ground rod
- this provides a path for electrons to flow between the object where static charge is building up and the ground
why do planes have static wicks/cars have earth belts?
provides a path for excess electrons to flow back into the atmosphere/ground, preventing static build up
how does sparking occur when fuelling cars?
- fuel flowing from pipe = friction
- static charge builds up in the fuel
- nozzle from pipe gains any static charge from the car when inserted in the car
- charge can jump to fuel tank which causes a spark/explosion/fire
how do smoke precipitators work?
- waste gases containing solid smoke particles pass through a negative grid
- the solid particles gain a negative charge
- smoke chimneys are lined with positive collection plates
- negative solid particles are attracted to the positive collection plates
- on contact the solid waste particles lose their charge and fall into the collecting trays
- so the waste gases emitted are free of solid particulate matter
how does insecticide spraying work?
- as insecticide is sprayed, a charge is induced in the droplets due to friction
- insecticide droplets all have the same charge
- the droplets repel each other creating a fine mist
- as the mist falls, this induces an opposite charge in the plants/crops
- droplets are then attracted to the oppositely charges plants/crops
- the advantage of this is that all of the plant/crop is covered with insecticide including the underside which prevents wastage and less will be blown away by the wind
how do photocopiers work?
- inside the photocopier, a drum rotates against a polythene drum charger
- the drum now has an induced positive charge
- light is then shone onto the original image which is reflected and then projected onto the positively charged drum
- in areas hit by the light (white areas), the drum loses its charge but stays positively charge in dark areas
- negatively charge
d toner is then sprinkled onto the drum
- the negatively charged toner is attracted to the remaining positive charge on the drum and sticks
- blank paper is rolled through the drum and picks up the toner (an image of the original image)
- the copy is heated to fuse the toner allowing it to stick permanently to the paper
how does spray painting work?
- a car is attached to a high voltage negative supply
- when paint leaves the spray nozzle, a positive charge is induced due to friction
- the paint droplets have the same charge so the repel each other which produces a fine mist
- the potential difference between the mist and car creates an electric field
- so the positive paint droplets follow the lines of force in the field allowing paint to be attracted to both the front and back of car parts
- the advantage of this is that cars are painted evenly, it takes less time and less paint is wasted
what is an electric field?
the region around a charged particle/object within which a force would be exerted on other charged particles or objects
which direction are electric field lines drawn in?
the direction positively charged ions would move in an electric field
