P2 topic 1 Flashcards
Why does a balloon stick to a wall after being rubbed against your clothes?
- The friction transfers electrons to the balloon, causing it to become negatively charged
- The charged balloon repels some of the electrons away from the surface of the wall, leaving it positively charged
- Opposites attract!
ion
a charged atom
What are examples of induced charge?
balloon rubbed against your clothes sticking to a wall, synthetic clothing clinging to your body, a stream of water being bent towards a charged insulator, a comb becoming charged when you are brushing your hair and then attracting strands
conductors
they allow electricity to flow through them easily- metals are good examples of electrical conductors- wires are made of copper
insulators
they prevent the flow of electricity- plastics are good examples- a plastic insulator surrounds the copper wire, preventing you from getting an electric shock when you touch them
How can static electricity be avoided?
Anti-static sprays, liquids and cloths can be used to prevent the build up of charge by allowing it to conduct away
What are some problems with static?
Dust and dirt can stick to the plastic cases of tv screens and computer monitors, synthetic clothes that have just come out of the tumble dryer can stick to you
What are the dangers associated with static electricity?
electric shocks can occur if you touch something with a large electric charge, potentially causing burns or stopping your heart; static charge building up in the refuelling of aircrafts and tankers could cause a spark (they must be earthed); static building up in flammable gases or in high concentrations of oxygen could cause an explosion; lightening is caused by charge building up in clouds and the energy having to be released somehow
lightning
caused by static electricity building up in clouds, eventually resulting in a huge spark to form between the ground and the cloud: a flow of charge through the atmosphere- it leaps to another part if the cloud or to the ground
electric current
the rate of flow of charge- measured with an ammeter connected in series
cell
a chemical device with its own positive and negative terminals which push electrons around a circuit
battery
a collection of cells, often joined together in series
what kind of current does a cell or battery provide?
direct current- this means that the electrons travel in one direction only
what is charge measured in?
coulombs
what is current due to in metals?
the flow of electrons
charge of an electron
-1.6 x 10-19 C
current
1 ampere when the rate of flow of charge is 1 coulomb per second
what is current conserved at a junction?
the total number of electrons entering a junction must be equal to the total number of electrons leaving the junction
resistance
the extent to which an electrical component restricts the flow of current in a circuit
resistance
the extent to which an electrical component restricts the flow of current in a circuit
voltmeter
measures the potential difference in volts across a component- it’s connected in parallel with the component
what happens as electrons travel round a circuit?
they transfer some of their electrical energy to other forms such as heat and light
potential difference
energy transferred per unit charge
what are electrostatic paint sprayers used on?
many metal objects
how do electrostatic paint sprayers work?
the object to be sprayed is connected to a negative supply; the sprayer charges the tiny droplets of paint as they emerge from the nozzle; charged droplets of paint repel each other and spread out to form a dispersed cloud; the positive droplets are attracted to the negatively charged object being sprayed
what are the advantages of using electrostatic paint sprayers?
less paint is used; object is given an even coating of paint; every part of the object attracts the paint- even the underside
what is the techniques also used for?
to spray plants with insecticides- the insecticide is given a positive charge and the plants acquire an negative charge by induction
what do closer lines signify in a magnetic field?
a stronger field
what do arrows in field lines show?
direction of the field
which direction will a positive object tend to move in?
the direction shown by the arrows
what can an insulator be charged by?
friction
what are the separated charges called?
induced charges
what’s a simple way of causing a transfer of charge?
simply rubbing a glass rod with a woollen cloth will cause a transfer of charge; wool gains electrics to become negatively charged; glass loses electrons and is left with an equal positive charge-static charge
how can all insulators be charged by friction?
some lose electrons by friction becoming positively charged; other insulators gain electrons by friction becoming negatively charged- each insulator acquired an equal but opposite charge
what is all matter made up of?
tiny atoms- each is about 0.0000002 mm in diameter
how much smaller is the nucleus than the diameter of the atom?
100 000 times smaller
what is used to find the charge on an insulator?
a gold-leaf electroscope- a metal did connects a metal cap to gold leaf
what will bringing a negatively charged rod close to the gold-leaf cap do?
it will repel the electrons down the metal rod- gold leaf moves away from the metal rod because they both have the same charge- the greater the charge, the further away the leaf moves
what does bringing a positively charged rod close to a gold-leaf cap do?
it will attract the electrons towards the cap, leaving the gold leaf and the metal rod with a positive charge- again, the gold leaf moved away from the metal rod because they both have the same charge
what can cause charges to separate?
certain clothing fibres can rub together and cause charges to separate- the crackling noise when you undress comes from tiny electrical sparks
what will happen if you bring your finger close to a charged insulator?
the electrons on the surface will jump the tiny distance of sit and travel through you to earth
how can most objects be made safe?
by earthing them- earthing involved placing a metal conductor between the object and the Earth to channel the charges safely to earth
why are aircraft and tanks earthed when fuelling?
fuelling then causes static as the fuel rubs against the pipe- the charges can build up and create a spark, igniting the fuel
why is lightning dangerous?
it can destroy buildings and start forest fires
how are talk buildings prevented from lightning strikes?
a lightning conductor is often installed at the top of the building- top of conductor has a pointed spike and bottom is embedded in ground; when a negatively charged cloud passes overhead it induces positive charges at top of lightning conductor; spike repels positive ions in air air towards cloud- this neutralises the cloud so there is no lightning
how can electrical shocks come from everyday objects?
walking on synthetic (nylon) carpet will charge carpet and you; you may get a shock when you are about to touch a metal tap or radiator; clothing can become electrically charged when rubbing against synthetic material of a car seat- you will get a shock as you get out of car
