physics - static electricity (11.1 - 11.10)

static electricity

build up of charge on insulating materials

11.1 how can an insulator be charged by friction?

charges cannot flow through insulator → other materials

2 insulators rubbed together

electrons transferred from one insulator → other

1 insulator gains electrons → - charge

1 insulator loses electrons → + charge

11.2 charge on object gaining electrons

negative

11.2 charge on object losing electrons

positive

11.3 what do like charges do?

repel

11.3 what do unlike charges do?

attract

11.4 shock from everyday objects - e.g.

walk across carpet - end up with unbalanced electric charge

p.d. between earth & you increases

touch conductor (e.g. metal tap) - electrons flow between tap & you

electrons flow in direction that removes excess charge

you become discharged/earthed

11.4 lightning

static electricity builds up in clouds due to friction between ice particles/water moved by air currents

charge large enough - charged particles travel through air between cloud & earth

causes lightning & thunder

11.4 attraction by induction - charged balloon attracted to wall

- balloon brought near wall

- electrons in wall repelled

surface of wall becomes + charged

no charges transferred from balloon

+ charge on wall induced

11.4 attraction by induction - charged comb picking up small pieces of paper

charged comb induces opposite charge in pieces of paper

comb attracts pieces of paper & picks them up

11.5 how does earthing remove excess charge?

connects charged object to earth

earthed by conductor - in earth

electrons flow in direction that removes excess charge

11.6 uses of electrostatic charges - insecticide sprayers

electrostatic spraying uses static electricity

electrodes on spray nozzle charge spray droplets as they pass

charged droplets repel each other & spread out

charged droplets attracted to plants by induction

less spray falls on ground

farmers use less spray

11.7 dangers of sparking - fuelling cars

charge can build up when fuel flows through pipe

sparks dangerous - fuel vapour could ignite

11.7 earthing - fuelling cars

at petrol stations, storage tanks, pipes & hoses are earthed

cars earthed through tyres - contain form of carbon that makes them conducting

you are earthed when touch metal of car/pump

11.8 electric field definition

region where electric charge experiences a force

how to draw field lines

never cross

field strongest where field lines closest together

show direction of force on charge in field

positive → negative

11.9 shape, direction & strength of electric field around point charge

away from positive

towards negative

field lines more concentrated = electric field stronger

11.9 shape, direction & strength of electric field between parallel plates

positive → negative

field lines more concentrated = electric field stronger

11.10 how does electric field help explain static electricity?

electric field: region where electric charge experiences a force

static electricity: build up of charge on insulating materials

charges produce force field around them - charged objects can attract/repel other objects without touching them