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physics > electricity > Flashcards

electricity Flashcards

1
Q

what is an electrical circuit

A

a closed loop with a battery or cell and something for electrons to flow through

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2
Q

what is the current

A

measure of flow of electrons around the circuit-(amps)A
it is like the water flowing through a hose

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3
Q

what is pd/voltage

A

force driving the flow of electron provided by cell or battery (V)
-pump that forces water along the pipe

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3
Q

what is resistance

A

anything that resists or opposes the flow of electrons(Ohms)
-similar to a partial blockage in pipe

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3
Q

what are the terminals

A

positive and negative the longer being positive
-current flows from positive to negative terminal as electrons are attracted to the oppositely charged positive terminal

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3
Q

what is v=ir

A

pd = current x resistance

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3
Q

what is the relationship between voltage and current if resistance is constant

A

they are directly proportional with v on the x axis and i on the y axis assuming the temperature is constant(if temp increases resistance increase)

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3
Q

what is the relationship of current and voltage with a filament lamp

A

as current flows wire heats up emitting light - this means it is very hot so resistance increases so curve gets less steep as you increase the current

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4
Q

what is the relation between a diode current and resistance

A

they only allow current to flow in 1 direction as they have very high resistance in the opposite direction-they only show current when pd is positive

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4
Q

what does it mean when the resistance is constant (fixed resistor)but the voltage and current are negative

A

the battery is attached the opposite way

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4
Q

for wires and resistors what and why will increasing the temp do

A

ions in the metal vibrate faster making it harder for electrons pass along the wire essentially increasing the resistance

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4
Q

what is charge

A

the measure of the total current that flowed over a certain period of time(Q) measured in coulombs(C)

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4
Q

what is the equation for charge time and current

A

Q(C)=I(A) x t(s)

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4
Q

what are the role of fuses in a circuit.what is the symbol

A

break if too much current flows through a circuit.
the symbol is a rectangle with a line straight through it

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4
Q

what are some places you may see leds being used

A

traffic lights
alarm clocks
led bulbs

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5
Q

how are ammeters connected

A

in series

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5
Q

how are voltmeters connected

A

in paralell

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5
Q

what are ldrs and thermistors

A

an ldr is a resistor whose resistance is dependent on the intensity of light-low resistance in bright light- can be used in automatic night lights/or burglary alarms

a thermistor has high resistance at low temps
can be used in car engines or electronic thermostats

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6
Q

what does the difference between series and parallel circuits change

A

the way we measure current , voltage and resistance

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7
Q

what are the negatives of series circuits

A

if 1 component is disconnected the whole series stops working

the pd is shared across all components

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8
Q

what is the total resistance of a circuit in series

A

the sum of each individuals resistance

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9
Q

do ammeters have resistance

A

yes but it is so tiny we can ignore them in our calculations

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10
Q

even if voltmeters are in parallel in a series circuit

A

we still treat the circuit in series

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11
Q

why would a component have a higher share of the voltage

A

if it had a greater resistance

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12
Q

what are the benefits of the multiple loops of parallel circuits

A

if a particular component break is still intact the overall circuit a

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13
Q

in parallel circuits what happens i f the pd is 12v

A

every component will have 12v across them

14
Q

what is difference in current in parallel vs series

A

in series-current is= across all components
in parallel i1=i2+i3

15
Q

what is the difference in pd

A

series-split between components
parallel-same across all components

16
Q

what is the difference in resistance

A

series-sum of all resistance
parallel-less than value of resistance over components

17
Q

what is the equation for power/pd /current

A

power or energy transferred in joules = pd x current

18
Q

what is the national grid

A

giant network of transformers and wires that distribute our electricity

19
Q

when does electricity demand peak in

A

the late evening and afternoon

20
Q

what does national grid have to transmit and what factors does this limit

A

we need high power
p=vi
however if we have high current this means there will be high resistance and generates lots of heat which dissipates

21
Q

how do we avoid get lots of power without wasting a lot of energy

A

voltage must be high and current must be very low

22
Q

what and why do we use to make the voltage really high in the national grid

A

step up transformers which increase voltage to about 400000v to minimise energy loss and decrease current

23
Q

what is the journey of electricity in the national grid

A

1) Generate electricity at the power station
2)increase voltage of electricity using step up transformers to 400000v
3)Wires transmit electricity using pylons
4)before reaching destination like a town we use step down transformers to 230v

24
Q

why do we use step down transformers

A

they lower voltage and increase current making it safe to use

25
Q

what are the 2 types of current

A

alternating and direct

26
Q

what makes alternating current alternating and how do we get it

A

when the current changes direction constantly by using an alternating pd that switches from positive and negative

27
Q

what is the current in the uk and frequency

A

alternating at 50hz frequency

28
Q

what does the frequency being 50hz mean

A

the voltage will go from +240v to -240v 50 times every second and so will the current

29
Q

what is direct current

A

produced by pd which is either positive or negative and never changes direction

30
Q

what are some items that run on direct current

A

cells and batteries in phone or calculator

31
Q

what does an oscilloscope do

A

show how voltage changes with time

32
Q

what are the 3 wires in the 3 core cable and what do they all have

A

live
neutral
earth

they are made of copper so they can conduct electricity and coated in a layer of insulating plastic for safety

33
Q

what colour is the live wire and what does it do

A

brown
provides alternating pd from mains supply

34
Q

what colour is the neutral wire and what does it do

A

blue
it completes the circuit by carrying away current(has a pd of 0)

35
Q

what colour is the earth wire and what does it do

A

it is striped green and yellow
has pd of 0v

stops appliance casing becoming live providing alternative pathway for current to flow away

36
Q

what do the pd of 0v for the earth and neutral wire help do

A

difference in voltage from the live wire is what causes electricity to pass from one to another

37
Q

why can we not touch the live wire

A

as we have 0 pd and it would cause a large current to flow through us as an electric shock

38
Q

what is a risk in using electricity

A

surges of current(from change in circuits or faults in circuit or appliance)which can cause fires or electric shocks or damage appliances

39
Q

what are fuses

A

thin piece of wire connected to live wire which when a surge goes through gains a huge amount of current alongside live wire and heats up and melts and breaking the circuits

40
Q

what should a fuse be compared to the rating of ur appliance

A

a few amps above
eg if a toaster has a 10a get a 13a so it only stops it at 13a

41
Q

what are the pros and cons of fuses

A

pros
-simple and cheap
cons
-permanently broken after single surge

42
Q

explain circuit breakers +advantages and disadvantages over fuses

A

they break circuit when there is a surge but just get tripped and turn off the circuit

-pros
-can easily be reset instead of having to be replaced
-cons
-more expensive than fuses

43
Q

how do we stop electric shocks

A

-earthing
-double insulate appliance (cover in plastic(doesnt conduct electricity) casing so there is no exposed metal
this doesnt need an earth wire

44
Q

what are used against surges of current

A

fuses and circuit breakers

45
Q

what is the rating of a fuse

A

current that causes fuse to break circuit

46
Q

what is static electricity

A

build up of charge on insulating materials

47
Q

what is the only thing transferred in static electricity

A

electrons

48
Q

what happens when an object gains more and more electrons

A

a pd between charged object and earthed object and if pd gets large enough the electrons will jump across causing a spark

49
Q

why cant 2 conducting materials build up charge

A

friction between them would cause the electrons to flow straight back

50
Q
A
51
Q

For electrons to flow what must happen

A

Circuit must be closed
Must be source of pd(battery or cell)

physics (9 decks)

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