What is static electricity?
Created when two insulators rub together and friction transfers electrons from surface to another. The matter also become charged -a positive static charge on the material that has lot electrons and an equal negative charge on the other
What happens to two electrically charged objects?
- they exert a force on each other
- opposite charges are attracted to each other while two of the same repel each other
- the forces get weaker the further apart you go
What happens with a balloon and static electricity?
- both surfaces start negatively and running transfers electrons
- Electrons are repelled by the negatively charged balloon so the electrons move further into the wall
- As protons cannot move this induces a positive charge in the surface closest to the balloon (the wall) causing it to attract to it
What effect does rubbing have?
Doesn’t make charge. Instead it separates and induces charge that were there all along
How does static electricity cause sparks?
- As static electricity builds up on an object, the potential differences between the objects and the earth (0V) increases
- if the P.D. Gets large enough, electrons and jump across the gap or an earthed conductor e.g. clothes -this is the spark
How is static electricity used in electrostatic precipitators?
- waste gases containing smoke particles pass through a negatively charged metal grid making them negative
- smoke parties attract to the positively charged collecting plates
- collecting plates are knocked to remove them meaning waste gases can leave without them as they cause breathing difficulties and building damage
- they become negatively charged as they transfer their charge to the plate
How is static electricity used for photocopiers?
- image of original document is projected onto positively charged copying plate
- where light falls onto the plate, the electrical charge leaks away
- negatively charged black toner particles are attracted to the remaining area
- paper is placed over plate and the toner transferred to the paper and heated to stick
How is refuelling dangerous?
- plastic isn’t a conductor of electricity so electrons flow is prevented and the pipe is not earthed
- static electricity may then build up which can produce a spark
- this could cause an explosion especially in fumes places and as fuel can be flammable
How are refuelling dangers overcome?
A grounding or earthing rod meaning any charge conducted to earth can’t build up as it is discharged -no sparks
How is lightening dangerous?
Ice particles rub together and build up static charge -positively charged top of the cloud and negatively charged bottom.
This builds up a huge voltage and if big enough electrons can jump through the air to the earth
How are dangers of lightening overcome?
Attaching an earthling rod to the tallest part of a building will provide and funnelled and direct route to the earth as it is a conductor.
-in earthing, electrons flow down the conductor to the ground if negative or up from the ground if they are positive
What is an electric field?
- a region where an elective to charge experiences a force
- the closer you get the stronger it is
How do you draw field lines?
- they go from positive to negative
- are at a right angle to the surface
- the closer the line (further in) the stronger the field is
What do parallel plates form?
Uniform fields
-if the field lines between charged objects point in the same direction they join up objects are attracted to each other
How does an insulator become charged through static electricity?
Through fiction which leads to a transfer of electrons
-the material gaining electrons become negatively charged and the one that is loosing them an equal positive charge
How is static electricity used in electrostatic sprayers?
- spray gun is charged charging the small droplets of paints. Each paint drop repels the others so you get a fine and even spray with little waste
- the painted object is given an opposite charge to attract the spray paint
How do insecticide sprays work?
- work in same way as electrostatic sprayers but the crops aren’t given an opposite charge, rather they charge by induction when the droplets come near them
- charged object attracts an uncharged object
