Static electricity Flashcards
principle of charges
like charges repel! unlike charges attract!
complete the sentence:
the closer the charges…
the stronger the forces
electric charge(a physical quantity)
is measured in coulombs, by a coulombmeter
electrical insulators vs conductors
ei-> the charged particles r unable to move abt freely while in ec they r
ei has a low ability to conduct electricity but ec has high
ei can b charged by friction & whn the insulators r charged the electrons remain at the surface whr the material has been rubbed but thn ec is by induction
example of ei is like glass and perspex and wood
ec is copper and iron and steel
electrostatic charging by friction/rubbing(EI!)
- b4 rubbing do note tht both materials r electronically neutral-> contain equal no. of protons n electrons
- since diff materials hv diff affinities for electrons, whn 2 materials r rubbed tgthr, the atoms at their surfaces r disturbed
- so some electrons frm one surface( eg glass rod, cloth, acetate rod) is transferred to another(silk, polythene rod and cloth)
- as the 1st material loses e it bcomes +vely charged while the othr one bcomes -vely charged since it gains e.
definition of insulator
material that does not allow e to flow through it freely
how to make charged insulator neutral?
heating and humid conditions
charging a conductor:
definition of induction
why can’t we use friction to charge a conductor?
process of charging a conductor w/o contact btwn the conductor n the charging body. conductors can b charged by induction n not friction bcos electricity can b easily transferred thru n away frm conductors
induction:
- place 2 neutral insulated metal spheres side by side such tht thy r in contact.
- bring a -vely-charged rod near but not touching sphere A. this will cause the electrons frm the sphere to b repelled to the furthest end, the right of sphere B. Now sphere A has excess +ve charges while B has excess -ve charges.
- while holding the charged rod in place, move sphere b from a
- remove the charged rod so now sphere a n b r =vely n -vely charged respectively-> equal no. of opposite charges
earthing:
using only a single metal conductor n using induction:
- bring a +vely/-vely charged rod near a neutral metal conductor on an insulating stand.
- the -ve/+ve charges are drawn towards the end near the end of the rod n the +ve/-ve charges r moved to the othr end
- w/o removing the rod, earth the +vely/-vely charged end of the sphere by touching it with ur hand
- if it is +vely charged-> e will cm up ur hand frm earth to neutralise it n if it is -vely charged-> e will move down to earth
- with the charged rod still in place, remove ur figer n stop the earthing process
- therefore once u remove the charged rod, the -ve/+ve charges will redistribute themselves thru the conductor causing it to b -vely/+vely charged.
discharge a charged conductor:
earthing
since electrons r free to move in conductors, whn we earth a charged conductor-provide a path for–> excess e to flow away frm the charged conductor, move down to earth, causing it to b neutral or for electrons to flow up frm earth to neutralise the excess +ve charges in the conductor making the conductor neutral
definition of electric field
is a region in which an electric charge experiences an electric force
electric force defintion(build on frm electric field)
is the attractive or repulsive force tht electric chqrge exert on one another.
complete the sentence:
field charges are strongest near…
the charged obj producing it
field lines do not…
cross!
electric field lines must be…
perpendicular to the surface
electric field lines that are further apart/closer together…
therefore, the strength of an electric field is indicated by…
indicate weaker electric field in the region/stronger electric field in the region
how close the field lines are to each other
direction of an electric field=
direction of the force tht would act on a small +ve charge
hazards and applications of electrostatics:
what is lightning?
lightning is n atmospheric discharge of electrostatic charges tht typically occur during thunderstorms
electrostatic charges r discharged to the nearest or sharpest obj on the ground which is why buildings have lightning conductors installed n ppl shld not swim in the open sea, play in an open field or hide under trees during thunderstorms
1. a thundercloud becomes electrically charged due to friction between water molecules in the thunderclouds n air particle in the atmosphere
2.-ve charges tend to gather at the bottom of the cloud
3. the -vely charged underside of the clouds repel the e near the surface of the earth n bcomes +vely charged
4. whn the accumulation of charges is large enough it can ionise the air particles nearby-> ionised air particles provide a conducting path for the electrons in the cloud to rch the earth. e tht follow this discharge path to the earth form LIGHTNING
5. induced +ve charges to form on the ground or building
what is a lightning conductor n how does it work?
lightning conductor r sharp spines tht allow the conc of +ve charges, lightning tends to strike tall or isolated structures so the lightning conductor protects tall buildings by providing a conducting path for -ve charges/e in the air to flow frm the top of a tall building to the earth
this prevents lightning frm damaging tall buildings bcos during fischarge,lightning ald b strongly attracted to conc +ve charges.
electrostatic discharge:
vehicles carrying fuels(hazard)
e charges can accumulate on the tracks/tankers due to friction btwn the road n the rotating tyres of the tankers so -ve charges acquire on the tyres.
when a sudden discharge occurs, it may cause sparks n ignite flammable iteans tht the truck may b carrying
how to prevent the flammable items on the truck frm catching fire?
a conductive strip/metal chain can b used which connects the metal body to the ground thus conducting electricity frm the ground to neutralise the +ve charges on the body pf the tanker/ provide an earthing path for excess charges
nowadays instead of metal chains synthetic rubbr tyres r used tht contain carbon to aid electric discharge in petrol tankers
how can we prevent electrostatic discharge from damage electronic equipment such as circuit boards n hard drives?
thy shld b packd in antistatic packaging which hv a thin layer of metallised film, which acts as an electrostatic shield for the sensitive electronic equipment n placed insdie due fo electrostatic discharge
how do photocopiers work?
they use static electricity to produce printed documents
1. inside a photocopier there is a metal drum which is coated with selenium which is a photoconductor(ie only conducts ecity in the presence of light)
2. the drum is (evenly) charged +vely by rotating the drum near a highly-charged wire
3. the original image to be photocopied is 2 b placed on a sheet of clear glass abv the drum n an intense beam of light is shone onto the image:
the lighter colored parts of the image reflect more light onto the drum below making the areas of the drum become discharged(& conducting)
the dark areas reflect less light and the corresponding region on the drum remain charged(insulating), therefore +ve charges remain on tht surface of the drum
4. as the drum continues rolling, the +vely charged image on the drum attracts the -vely chargd toner powder in the toner cartridge
5. a +vely charged sheet of paper is passed ovr the drum surface so the -vely charged toner powder will b attracted away frm the drum to the paper.
6. the sheet of paper is heated(heating-> discharging of insulator, so tht the electrons dont like flow away) & pressed-> fuses the toner to the paper permanently.
