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physics Jack Martin > electricity (inc mains + static) > Flashcards

electricity (inc mains + static) Flashcards

(77 cards)

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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
length
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
filament lamp
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
26
diode / LED graph
_/ cruved graph going up
27
diode /LED
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
28
thermistors /LDRs
made up of semi- conducting material that changes resistance depending on the environment
29
thermistor
resistor changes with temperature useful for temperature control eg ovens kettles fridges thermostats
30
thermistor graph
as temp. increases resistance decreases non- linear inverse relationship (curve) because… - heat energy releases more free electrons to flow
31
LDR
light dependent resistor resistance changes with brightness of light (light intensity) useful for sending light changes eg control night lights
32
LDR graph
as brightness increases resistance decreases non- linear inverse relationship because… - light energy releases more free electrons to flow
33
power
rate of transfer of energy measured in watts (W)
34
power (Et) equation
E = Pt Energy /work done = power x time
35
power (IV) equation
P = IV
36
energy (Itv) equation
E = ItV
37
why do appliances get hot
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
power of lamp experiment
connect big and little lamp in series then in parallel note brightest then calculate power to see if it matches
39
battery electricity
provide low voltage d.c electricity dc is direct current (flows in one direction +>-)
40
mains electricity
provide 230V ac electricity ac is alternating current (continuously changes direction) frequency of 50Hz
41
plug
earth - green live - brown neutral - blue fuse flex (cable) flex grip
42
plug mistakes
wires connected wrong exposed copper wire flex not under grip wrong fuse
43
what makes a plug / wire safe to use
double insulated with plastic casing
44
ohms law
current is proportional to voltage providing temp. of resistor doesn’t change
45
fuse symbol
rectangle w line theough
46
variable resistors
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
way diode is connected
flows +>-
48
fuse
connected to live wire protects APPLIANCE from too high current which could damage it
49
fuse rating
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
fuse blows
fuse wire melts and breaks circuit
51
live wire
brown carried current into appliance
52
neutral wire
blue carried current away from appliance
53
earth wire
green/ yellow - protects USER from electric shock is fault occurs and appliance becomes live - connected to metal casing of appliance away from ground
54
normal operation of kettle
current flow in live wire and out neuteal
55
fault occurs in kettle
- 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
double insulated
has a plastic insulator casing so doenst need earth wure
57
alternative to fuse - circuit breaker
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
alternative to fuse - RCD or RCCB
detects if there’s a difference between the current in live and neutral wires - fault must’ve occurred and trips the circuit breaker
59
what type of material can be charged up
insukators
60
how to charge up
- 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
friction / electron transfer
if gain - charge if loose + charge the direction of transfer depends on objects
62
what happens if an already charged object goes near another object
it will induce a charge onto the other object
63
like charges
repel
64
opposite charges
attract
65
how does charged objects lose charge
to become neutral it must DISCHARGE has to connect object to EARTH with conductor
66
can static charge move
no
67
static charge
builds up in one place and is not free to move (on an insulator )
68
as charge builds up so does …
voltage pd between charged objects and earth (0V) increases
69
spark
if voltage is large electrons can jump between object and earth
70
investigating static electricity
- 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
van de graaff generatir
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
dangers of static electricity
lighting refuelling a plane refuelling vehicle
73
uses of static electricity
ink jets printers photocopiers chimney filter electrostatic crop sprayer
74
lightning - how to prevent danger
tall buildings have lightning conductors on top which earths the building
75
refuelling a plane - how to prevent danger
have earthing cable (conductor ) to prevent charge building up and allow it to be discharged
76
electrical hazards
- water + electricity - could reach high temp - damaged equipment is a hazard - overloaded sockets - trip hazard of wires
77
advantage of series/ parallel
series - one switch controls all parallel - if one breaks other is fine

physics Jack Martin (19 decks)

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