electricty Flashcards
(39 cards)
according to atom theory, what are atoms?
building blocks of all matter
what do atoms consist of
protons neutrons electrons
explain the charge of atoms
all objects either positively or negatively charged or electrically neutral (no net charge)
net means extra so there are equal amounts of positive and negative charges so there is no excess and balance each other
when is an object said to be charged
when there is an excess of one particular type of charge
where are positive charges
fixed in nucleus of atoms and cannot move
where are negative charges
located outside of nucleus in electron shells where if given enough energy where they break free of bonds to atom and become free electrons
how do positive charges move
when an atom splits and under high temperatures
this is not a natural process
how can you charge an object
by friction
by electrostatic induction
how can one charge by friction
when a neutral polyethelane/polythene rod is rubbed against a piece of cloth, the cloth gives up negative electrons to the rod leaving the cloth with a positive charge and the rod with the negative charge
when a an originally neutral Perspex rod rubes with a piece of cloth the perspex gives up electrons to the cloth leaving the cloth with a negative charge and the rod with a positive charge
explain charging by electrostatic induction
two metal spheres x and y are placed on an insulator stand
they are both originally neutral
two spheres are placed in electrical contact or touching and negatively charged rod is brought close to them
this causes electrons closest to rod to be repelled toward sphere Y
with rod still in place the spheres are separated leaving x with a net positive charge and y with a net negative charge
the charged rod is then removed
what happens when a negatively charged rod is brought close to an uncharged electrically neutral conductor
conductor becomes attracted to rod
because negatively charged rod will cause free electron in conductor to be repelled away from rod leading to the side of the conductor closest to rod with positive charge
hence the positive side of conductor attracted to positive charged rod
what happens when a negatively charged rod is brought close to an uncharged electrically neutral insulator
since there are no free electrons to move away from rod atoms comprising material become distorted so that the electrons trapped in their shells try to move as far away from negatively charged rod as possible
what are the four properties of charges
opposite charges attract each other
like charges repel each other
further away charges are the weaker the forces of attraction between them
force between charges inversely proportional to distance between them
define conductor
has many free electrons that move through material allowing a current to flow
define insulator
has no free electrons so it prevents a current from flowing through it
define semi conductor
poor conductor and poor insulator
so that it allows a small amount of current to pass through it since it has a few free electrons
define current
electrons moving in specific direction where the flow of electrons which concentrates a property
define static electricity
excess of charges where it stays in one place that is unstable and wants to move
list 5 risks of static electicity
electric shock due to flow of current through the body causing a person to feel everything from an uncomfortable zap to a burn to stopping the heart
fires and explosions due to ignition of flammable and explosive mixtures
production disturbances in processing of paper plastic composites powder granules liquids
damage to electronic equipment and components from electrostatic discharge
damage to mechanical equipment such as bearings due to sparking through oil films on bearing surfaces
explain the use of the lightning rod or arrestor
lightning rod is placed on very tall buildings on a way of preventing lightning
comprised of some sort of conductor such as silver or copper that is spiked at one end and the other is connected to a metal plate in the ground where its angle of curvature allows for bigger SA so there are more charges
negatively charged thunder cloud causes electron to be repelled down lightning rod to ground which leaves spiked top of rod with positive charges
positive charge causes electron to form air molecules surrounding spiked rod to be removed leaving air molecules with positive charge
these positively charged air molecules repelled down by rod upwards to negatively charged cloud
called electric wind and cancels charge in cloud preventing lightning
what is the symbol of charge
Q
what are charges measured in
coulombs C
what are coulombs
amount of charge flowing through the conductor when a current of one ampere flows for a time of one second
define electric current
rate of flow of charge
I
