static electricity Flashcards
electrical conductors
- have free electrons that are delocalised and can move freely in the material
electrostatic charging by friction for insulators
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when both objects are rubbed together, the electrons from the surface of one object are removed by friction and transferred to the surface of another object
woollen cloth -> positively charged
- loses some electrons and consequently gains an equal and opposite positive charges
polythene strip -> negatively charged
- gains electrons
- excess of electrons
electrostatic induction
process of charging a conductor without any contact with the charging body
earth
any large neutral conductor from which electrons may be taken or given without it become noticeably charged itself
charging by electrostatic induction for SINGLE electrical conductor
- negatively charged rod is brought near the uncharged metal ball (mounted onto insulating stand) w/o it touching the metal ball
- an electric field is set up by the negative charges on the rod
- an electrical force of repulsion is exerted on the free electrons in the uncharged conductor which then move towards the right side of the conductor, away from the rod
- this results in positive induced charges on the left side of the conductor and an equal quantity of negatively induced charges on the right side of the conductor
- w/o removing the negatively charged rod, earth the conductor
- disconnect the wire from the conductor
- remove the negatively charged rod
- -IMPORTANT—
- result in a charge opposite to that of charged rod
- charged rod does not touch conductor & does not lose its own charge
charging by electrostatic induction for TWO electrical conductors
- 2 uncharged conductors on insulator stands are brought into contact with one another
- a negatively charged rod is brought near one of the spheres, sphere A
- the negative charges on the rod sets up an electric field and exerts a repulsive force on the negatively charged electrons on the sphere. this causes electrons from sphere A to be repelled to the far end of sphere B. sphere A will have positive induced charges due to a deficit of electrons while sphere B will have an equal and opposite negative induced charges due to an excess of electrons
- with the negatively charged rod in place, spheres A and B are separated far apart
- remove the negatively charged rod. sphere A and B will have equal amounts of opposite charges. net charge on charged rod remains unchanged
charging an electrical conductor by contact
- bring a charged metal rod in contact with the metal sphere to be charged
metal sphere to be charged will have the same charge as the charged metal rod
- remove the rod
what does it mean to neutralise/discharge a charged body
it is to remove the excess charges from it
how to neutralise a charged conductor
- use earth
- provides a path for electrons to flow away or towards the charged conductor and neutralise it
electric field
it is a region of space surrounding a charge or charged particle where a small test charge experiences an electric force
state and explain what happens to the spheres when they go through the metal cylinder which is maintained at a high voltage
they become positively charged, as free electrons on the conducting spheres and surface electrons on the non-conducting spheres feet attracted to the positive terminal of the voltage supply and leave the spheres
describe the movement of the electrons which take place when the switch is closed and sphere L becomes charged
when the switch is closed, electrons on L move to the positive terminal of the high voltage supply. L has less electrons and becomes positively charged
explain why the conducting spheres fell off from the roller while the non-conducting spheres have to be scrapped off
electrons from the metal roller neutralise the positive charges in the conducting spheres
the conducting spheres are no longer attracted to the metal roller and thus fall off
for non-conducting spheres, electrons from the metal roller neutralise only the surface charges in contact with the roller
the non-conducting spheres remain positively charged and attracted to the negatively charged roller
electrical insulators
- do not have free electrons
- charged easily by friction (rubbing)
electrons are transferred from one material to another but they remain on the surface
