electricity Flashcards
1
Q
charging by friction
A
- friction causes displacement of electrons
- When 2 insulators move relative to each other, friction can result in electrons being transferred from one to the other which can result in both objects becoming electrically charged.
- One of the objects (the one that lost electrons) has +ve charge, and the other (the one that gained electrons) has -ve charge, depending on the nature of the materials
- e.g. plastic being rubbed by a duster; hair being combed; an aeroplane moving through the air.
2
Q
induction
A
- when a neutral object becomes charged by being placed near a charged object
- the neutral object is oppositely charged to the already charged object
3
Q
repulsion vs attraction
A
- like charges repel each other
- unlike charges attract each other
- the larger the charges, the larger the force
- the larger the distance of separation, the smaller the force
4
Q
conductors and charge
A
- it is possible for 2 conductors to charge each other by friction. However, the fact that electrons in them are free to move means that any charge transfer between them will instantly return, given that the objects must be in contact for friction to occur between them.
- they will only retain that charge if they are insulated from their surroundings. If they are not insulated, then any charge that builds up will leak away
5
Q
photocopier
A
- The scanning process results in charge being placed on the paper at the locations where the image is to be printed
- The paper is then exposed to toner powder, which ‘sticks’ to the paper at those locations as a result of electrostatic induction
- The paper is then heated so that the toner powder melts and then re-solidifies on the paper
6
Q
aircraft refuelling
A
- When aircraft are refuelled, large volumes of fuel flow through the pipe very quickly creating large amounts of friction
- This results in the fuel and the pipe becoming charged
- Sparking presents a significant risk of explosion of the fuel in the fuel tank, so, the tank and pipe are always earthed beforehand.
- This earthing prevents the build-up of charge and so eliminates the risk of explosion.
7
Q
direct current (DC)
A
- a current that is always in the same direction
- cells/batteries are sources of dc
8
Q
alternating current (AC)
A
- a current that repeatedly changes direction, usually very rapidly
- Generators in power stations produce ac
- its waveform must include a graph line that is sometimes above the axis and sometimes below it
9
Q
diode
A
- A diode only allows current in one direction (the direction of the arrow on the symbol)
- The output from a power supply from mains electricity can be converted from ac to dc using diodes as a ‘rectifier’
- for current to flow the diode arrowhead must point from the +ve terminal of the battery to the -ve terminal
10
Q
conductors
A
- material that allows flow of charge
- e.g: all metals (because of the presence of delocalised electrons which can flow through the metal), particularly copper, gold and silver, carbon (in the form of graphite), ionic solutions
11
Q
insulators
A
- material in which electric current does not flow freely
- e.g: most non-metals, particularly plastics, rubber, dry wood, air, vacuum
12
Q
water
A
Water, unless extremely pure, is a conductor, so wet or damp materials are not good insulators
13
Q
cables
A
An electric cable usually uses an insulator on the outside and a conductor on the inside
14
Q
directions of flow
A
- current flows from the +ve end of a conductor to the -ve end
- electrons flow from the -ve end of a conductor to the +ve end
15
Q
electrolytes
A
- a substance that conducts electricity when dissolved in water
- this is because it contains charged ions
- If two electrodes are placed in the liquid and a voltage is applied across them, the cations move towards the -ve cathode, and the anions move towards the +ve anode
