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Physics > Electricity > Flashcards

Electricity Flashcards

1
Q

what is double insulation for electrical appliances

A

if the appliance is made of a plastic casing or the electrics are completely encased in a plastic cover. This means that if a fault develops inside, there is still no route for the current to take to shock you.

(many electrical appliances only have metal casings eg. cookers, washing machines, and fridges)

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2
Q

what is insulation for electrical appliances

A

the plastic coating covering wires

plastic = insulator so current can’t flow

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3
Q

What is earthing and why is it needed (safety in electric appliances)

A

when one end of the earth wire is attached to the metal case. This provides a lower resistance route for the current to take, rather than through the user.

Needed if the live wire comes loose and touches the metal case

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4
Q

What is a fuse and how does it work

A

the fuse consists of a thin wire in a ceramic case

when the current flows through the wire, depending on the limit of the fuse, there will become a point at which, if the current is too high, the fuse wire will heat up and melt. this breaks the circuit and isolates the appliance from the live wire.

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5
Q

How do circuit breakers work and what do they do

A

they break the circuit (similarly to fuses) using electromagnetics which means they are able to be reset.

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6
Q

what colour is the earth wire and where is it on the plug

A

green and yellow
in the middle

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7
Q

what colour is the live wire and where is it on the plug

A

brown
on the right

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8
Q

what colour is the neutral wire and where is it on the plug

A

blue
on the left

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9
Q

which wire does the fuse sit next to

A

live wire

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10
Q

why is long cables a hazard of electricity

A

long cables have larger resistances which means they heat up easier and cause a can fire (resistance is proportional to length of wire)

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11
Q

how does the current in a resistor result in the electrical transfer of energy and an increase in temperature

A

As current in passed through a wire, the free electrons will collide with the lattice of metal ions (which will be vibrating in place). as they do so they will transfer their energy in the form of heat. if you increase the current, more energy is transferred to the metal ions and the wire heats up more.

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12
Q

equation for Power

A

Power = current x voltage

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13
Q

equation for energy transferred

A

energy = power x time

( energy = current x voltage x time)

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14
Q

what is direct current

A

current (or voltage) that travels in one direction only

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15
Q

what is alternating current

A

current (or voltage) that changes direction continuously

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16
Q

what kind of current powers the mains supply

A

Alternating Current

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17
Q

what kind of current does a battery supply

A

Direct current

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18
Q

4 characteristics of the mains supply

A
  • AC
  • not portable
  • high voltage
  • does not need replacing
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19
Q

4 characteristics of the battery supply

A
  • DC
  • portable
  • low voltage
  • needs replacing/recharging
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20
Q

what is the rule about voltage in a series circuit

A

voltage is shared across the components SO the total voltage is the sum of the voltages across all the of them

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21
Q

equation linking voltage, current and resistance

A

voltage = current x resistance

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22
Q

what is the rule about current in a series circuit

A

the current across each of the components is the same

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23
Q

what is the rule about voltage in a parallel circuit

A

the voltage across each of the components is the same

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24
Q

what is the rule about current in a parallel circuit

A

the total current in the main circuit is the sum of the currents in the branches

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25
Q

advantages of using a parallel circuit for a network of lights

A
  • each bulb gets the full battery voltage
  • each one can be switched off independently
  • if one fails the rest can all still work
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26
Q

what does the graph representing voltage (x axis) vs current (y axis) look like for a filament bulb

A

on a cross shaped graph:

a shallow bowl shape until the origin the a shallow dome shape after that

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27
Q

what does the graph representing voltage (x axis) vs current (y axis) look like for a diode

A

on a cross shaped graph:

no current through the minus voltages then after the origin it slopes up slowly

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28
Q

what does the graph representing voltage (x axis) vs current (y axis) look like for a wire

A

on a cross shaped graph:

straight line through the origin.
- constant gradient

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29
Q

in which direction does current flow in a cell

A

from the positive terminal to the negative terminal

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30
Q

what is current in terms of particles

A

the flow of negatively charged electrons

31
Q

what is potential difference

A

the amount of energy transferred per unit of charge passing through the terminals (voltage)

32
Q

what is a volt equivalent to

A

1 joule per coulomb

33
Q

what is resistance

A

the opposition to current

34
Q

what is the resistance of a good conductor compared to a bad conductor

A

good conductors - low resistance
bad conductors - high resistance

35
Q

what is 1 ohm equivalent to

A

1 volt per ampere

36
Q

what is the current across a series circuit

A

the same value at any point

37
Q

how does increasing the number of components in a series circuit affect the current

A

it increases the resistance so decreases the current

38
Q

at a junction in a parallel circuit what happens to current and why

A

it is conserved (the current going in is the same as the current going out

this is because current is the flow of electrons which are physical matter so can’t be created or destroyed. so when they reach a junction some will go one way and the rest the other

39
Q

how does current behave across a parallel circuit and why

A

divides across the branches

depends on what components are causing resistance in that branch

40
Q

which is the positive and negative end of the cell in a circuit diagram

A
41
Q

how does voltage behave in a series circuit

A

shared between components

42
Q

how does voltage behave in a parallel circuit

A

same across all components

43
Q

advantages of a series circuit

A
  • fewer wires
  • all components controlled by single swicth
44
Q

disadvantages of a series circuit

A
  • the components can’t be controlled separately
  • if one component breaks they all stop working
45
Q

advantages of a parallel circuit

A
  • components can be individually controlled
  • if one component breaks the other still work
46
Q

disadvantages of a parallel circuit

A
  • many wires needed
  • all components have the same voltage supply so difficult is components need different voltages
47
Q

how do you calculate the total combined resistance of resistors in series

A

add them up

48
Q

what does the IV graph of a wire look like

A
49
Q

what does the IV graph of a fixed resistor look like

A
50
Q

what does the IV graph of a filament lamp look like and why

A
  • as current increases the temp of lamp increases
  • higher temp causes atoms to vibrate more
  • causes an increase in resistance because it is harder for the electrons to flow through
  • resistance opposes current so current increases at SLOWER RATE
51
Q

what does the IV graph of a diode look like

A
52
Q

what is the role of a diode

A

to only allow current to flow in one direction by having a very high resistance in the other direction

53
Q

in what direction can the current flow when this diode is in the circuit

A

to the right

54
Q

what is the symbol of a diode

A
55
Q

what is the symbol of a variable resistor

A
56
Q

what can be used to indicate the presence of current in a circuit

A
  • lamps and LEDs
57
Q

what is current

A

the rate of flow of charge

58
Q

what is electric current in solid metallic conductors

A

the flow of negatively charged electrons

59
Q

why is current conserved at a junction in a circuit

A

because junctions can’t store current and it can’t just disappear into thin air because charge is conserved. therefore the total amount of current flowing through the circuit must be constant

60
Q

how does the voltage across two components in parallel compare

A

it’s the same

61
Q

what is voltage

A

the energy transferred per unit charge passed

62
Q

what are some common hazards of electricity that cause electrocution

A

Damaged Insulation – if someone touches an exposed piece of wire

Overheating of cables – This could cause a fire or melt the insulation, exposing live wires

Damp conditions – the moisture could conduct electricity either causing a short circuit within a device (which could cause a fire) or posing an electrocution risk

63
Q

examples of conductors

A

Silver
Copper
Aluminium
Steel

64
Q

what is a conductor

A

a material that allows charge to flow through it easily

65
Q

examples of insulators

A

glass, plastic, rubber, air, and wood

66
Q

practical: investigate how insulating materials can be charged by friction

A
  • rub the ends of the polythene rod with cloth
  • without touching the ends, suspend the rod from the stand
  • take a (perspex) rod and rub it with another cloth
  • bring the two rods together, without touching, and record any observations
  • repeat for different materials
  • if same repel if opposite attract
67
Q

what type of materials retain charge

A

insulators

68
Q

what is a non contact force

A

a force that acts on an object without being physically in contact with it

eg electrostatics

69
Q

uses of electrostatics

A

inkjet printer
photocopier
insecticide sprayer

70
Q

how do photocopiers use electrostatic charges

A
  • image of document is projected onto a positively charged copying plate
  • plate loses its charge in light areas
  • a negatively charged black toner powder is applied to plate (sticks to opposite charge)
  • toner transferred onto sheet of paper
  • paper is heated so that the powder sticks
71
Q

what are the two dangers of a spark

A
  • explosion/fire
  • electrocution
72
Q

how can you reduce the dangers of electrostatic charge

A

earth is by connecting the object to the earth with a conductor

73
Q

what is the electrostatic danger when refueling vehicles

A
  • fuel is very flammable and runs through pipes at very fast rate
  • friction causes charge to build up
  • if a spark occurred, explosion

Physics (13 decks)

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