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physics > electricity (inc mains + static) > Flashcards

electricity (inc mains + static) Flashcards

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1
Q

current (I)

A

the RATE of flow of charge
measured by ammeter (A)
- series = same throughout
- parallel = splits at a junction

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2
Q

ammeter symbol

A

A

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3
Q

voltmeter symbol

A

V

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4
Q

variable resistor

A

square with arrow theough

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5
Q

thermistor symbol

A

square with _/line through

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6
Q

ldr symbol

A

square with circle round and arrows pointing towards

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7
Q

diode symbol

A

play button with circle round

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8
Q

led

A

diode symbol with arrows pointing away

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9
Q

resistor symbol

A

sauare

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10
Q

current equation

A

Q = It
- charge (C) = current (A) x time (secs)

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11
Q

actual current flow directions

A

->+
electrons attracted to + terminal

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12
Q

conventional direction of current flow

A

+>-

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13
Q

voltage (potential difference)

A

measure of how much energy (E) the charges (Q) are carrying
measured with voltmeter (V)
- series = splits between components
- parallel = each branch receives same voltage

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14
Q

voltmeter

A

measured voltage
compares energy charges carried into/out of a component and reads the differences

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15
Q

voltage equation

A

E= VQ
- energy transferred (J)= voltage (V) x charge (C)

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16
Q

charge (Q)

A

made up trillions of electrons in wires flowing round circuit
gain energy from battery and deliver to components
measured in coulombs (C)

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17
Q

equation linking VIR

A

V = IR
voltage (V) = current (A) x resistance (ohms)

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18
Q

resistance

A

limits the flow of current
hugh R = low I
low R = high I
measured using ohmmeter (in ohms)
all components have some resistance

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19
Q

factors that affect resistance

A

material
lengthe
thickness
temperature

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20
Q

measuring resistance

A

can measure resistance using a circuit R = V/I

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21
Q

VIR circuit problems solving

A
  • write down all values you know / work out
  • see if you can use V = IR
  • series - Rt = R1 + R2 total resistance INCREASES
  • parallel - Rt = Vt/ If total resistance DECREASES
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22
Q

fixed resistor graph

A

straight line - through origin
- linear relationship between current and voltage
- current is proportional to voltage

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23
Q

fixed resistor

A

resistor is Ohmic conductor
- follows Ohms law
OHMS LAW - current is proportional to the voltage providing temp of resistor doesn’t change

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24
Q

filament lamp graph

A

S - curved graph
for each interval increase in V the I increases by a smaller amount

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25
Q

filament lamp

A

doenst obey ohms law
- resistance of lamp increases due to it getting hot
- atoms in filament vibrate faster causing more collisions w electrons which slows them down

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26
Q

diode / LED graph

A

_/ cruved graph going up

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27
Q

diode /LED

A

only allows current to flow in 1 direction
when connected the wrong way have infinite R
voltage must exceed threshold voltage before conducting
sensitive to large currents so a resistor is used to prevent the LED from blowing if too much current flows

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28
Q

thermistors /LDRs

A

made up of semi- conducting material that changes resistance depending on the environment

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29
Q

thermistor

A

resistor changes with temperature
useful for temperature control
eg ovens kettles fridges thermostats

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30
Q

thermistor graph

A

as temp. increases resistance decreases non- linear inverse relationship (curve) because…
- heat energy releases more free electrons to flow

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31
Q

LDR

A

light dependent resistor
resistance changes with brightness of light (light intensity)
useful for sending light changes
eg control night lights

32
Q

LDR graph

A

as brightness increases resistance decreases
non- linear inverse relationship because…
- light energy releases more free electrons to flow

33
Q

power

A

rate of transfer of energy
measured in watts (W)

34
Q

power (Et) equation

A

E = Pt
Energy /work done = power x time

35
Q

power (IV) equation

A

P = IV

36
Q

energy (Itv) equation

A

E = ItV

37
Q

why do appliances get hot

A

appliances transfer electrical energy into heat
due to electrons colliding with atoms in the wire
appliances left running transfer electrical energy onto other types

38
Q

power of lamp experiment

A

connect big and little lamp in series then in parallel
note brightest then calculate power to see if it matches

39
Q

battery electricity

A

provide low voltage d.c electricity
dc is direct current (flows in one direction +>-)

40
Q

mains electricity

A

provide 230V ac electricity
ac is alternating current (continuously changes direction)
frequency of 50Hz

41
Q

plug

A

earth - green
live - brown
neutral - blue
fuse
flex (cable)
flex grip

42
Q

plug mistakes

A

wires connected wrong
exposed copper wire
flex not under grip
wrong fuse

43
Q

what makes a plug / wire safe to use

A

double insulated with plastic casing

44
Q

ohms law

A

current is proportional to voltage providing temp. of resistor doesn’t change

45
Q

fuse symbol

A

rectangle w line theough

46
Q

variable resistors

A

can change size of current and resistance
can control the speed of motor and be used as dimmer switches
CANNOT INCREASE AMOUNT OF CURRENT FLOWING

47
Q

way diode is connected

A

flows +>-

48
Q

fuse

A

connected to live wire
protects APPLIANCE
from too high current which could damage it

49
Q

fuse rating

A

maximum current it will allow through before it blows
work out using P= IV
- fuse too low - would blow as soon as use appliance
- fuse too high - could allow a high current into appliance and damage it

50
Q

fuse blows

A

fuse wire melts and breaks circuit

51
Q

live wire

A

brown
carried current into appliance

52
Q

neutral wire

A

blue
carried current away from appliance

53
Q

earth wire

A

green/ yellow
- protects USER from electric shock is fault occurs and appliance becomes live
- connected to metal casing of appliance away from ground

54
Q

normal operation of kettle

A

current flow in live wire and out neuteal

55
Q

fault occurs in kettle

A
  • if something breaks + occurs metal casing of appliance to carry current
  • would cause electric shock if touches
  • earth wire is connected to casing and carries current to ground outside
  • earth has low R so high I flows which blows the fuse and stops I flowing so appliance is safe
56
Q

double insulated

A

has a plastic insulator casing so doenst need earth wure

57
Q

alternative to fuse - circuit breaker

A

will trip a switch is current exceeds particular value
can be reset instead of replaced and reacts quicker
electromagnet attracts open switch if currents too high

58
Q

alternative to fuse - RCD or RCCB

A

detects if there’s a difference between the current in live and neutral wires - fault must’ve occurred and trips the circuit breaker

59
Q

what type of material can be charged up

A

insukators

60
Q

how to charge up

A
  • friction - causes electron transfer (like a cloth and rod rubbing against each other)
  • induction - already charged object will induce a charge if brought near to another object (like a balloon sticking to wall)
61
Q

friction / electron transfer

A

if gain - charge
if loose + charge
the direction of transfer depends on objects

62
Q

what happens if an already charged object goes near another object

A

it will induce a charge onto the other object

63
Q

like charges

A

repel

64
Q

opposite charges

A

attract

65
Q

how does charged objects lose charge

A

to become neutral it must DISCHARGE
has to connect object to EARTH with conductor

66
Q

can static charge move

A

no

67
Q

static charge

A

builds up in one place and is not free to move (on an insulator )

68
Q

as charge builds up so does …

A

voltage
pd between charged objects and earth (0V) increases

69
Q

spark

A

if voltage is large electrons can jump between object and earth

70
Q

investigating static electricity

A
  • rub balloon against hair - balloons charged- balloon can pick up little bits of paper
  • rub rod with cloth - rod is charged - rod can bend a stream of water
  • rub two rods of diff. materials with cloth - both rods will have charge - rods will either attract or repel depending if they have diff. or similar charges
71
Q

van de graaff generatir

A

electrostatic charge is built up on the metal dome
if you stand on an insulated block put your hands on the dome your body gets a charge
each hair has the same charge so they repel and spread

72
Q

dangers of static electricity

A

lighting refuelling a plane refuelling vehicle

73
Q

uses of static electricity

A

ink jets
printers
photocopiers
chimney filter
electrostatic crop sprayer

74
Q

lightning - how to prevent danger

A

tall buildings have lightning conductors on top which earths the building

75
Q

refuelling a plane - how to prevent danger

A

have earthing cable (conductor ) to prevent charge building up and allow it to be discharged

76
Q

electrical hazards

A
  • water + electricity
  • could reach high temp
  • damaged equipment is a hazard
  • overloaded sockets
  • trip hazard of wires
77
Q

advantage of series/ parallel

A

series - one switch controls all
parallel - if one breaks other is fine

physics (19 decks)

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