SP11 Static Electricity

SP11a Charges and Static Electricity

Insulators - collect charge e.g. plastics
Rub acetate roll with duster - electrons move from acetate to duster. Duster is negatively charged and vice versa.
If rub polythene with duster - electrons move from duster to polythene. Polythene now negatively charge and vice versa.
Same charge - repel
Different charge - attract
Static electricity - unbalanced electric charge on surface or object because charge cannot flow away.
Charge by induction - when an object is charged by bringing another near it, with no charge being transferred. E.g. when a ballon that is -ve is brought to a wall, the electrons in wall are repelled and +ve charge is left , so ball is attracted.

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Discharged/Earthed - when electrons flow in whichever direction removes the excess charge if there is an unbalanced electric charge.
Lightning - static electricity builds up in clouds due to friction of ice and water particles by air currents. When charge is big enough, charged particles travel between cloud and earth in air.
Buildings are earthed - lightning conductors made of metal from their tops to earth.
Sparks and refulling - fuel vapor may ignite because plane becomes charged when flying. Charge may build up when fuel flows through fuel pipe and aircraft, so bonding line is connected to earth and plane.
Electrostatic spraying - i.e. spraying crops with insectiside. Electrodes in nozzle charges spray particles. Particles spread - repel each other and attracted to plant by induction. Farmers uses less.

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Force Field - volume of space around an object in which another object can experience a force.
Electrical field - a charged object has a force field around it.
Point charge - charge at the single point of the electric fields.
Field lines - never cross, show where field is strongest (strong - lines are close together), direction of force on a charge in field, start at +ve object and end on -ve object.
Uniform - where the electric field is the same in all places between two charged plates.

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