electricity

Question 1

what is an electrical circuit

Answer 1

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

Question 2

what is the current

Answer 2

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

Question 3

what is pd/voltage

Answer 3

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

Question 3

what is resistance

Answer 3

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

Question 3

what are the terminals

Answer 3

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

Question 3

what is v=ir

Answer 3

pd = current x resistance

Question 3

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

Answer 3

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)

Question 3

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

Answer 3

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

Question 4

what is the relation between a diode current and resistance

Answer 4

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

Question 4

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

Answer 4

the battery is attached the opposite way

Question 4

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

Answer 4

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

Question 4

what is charge

Answer 4

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

Question 4

what is the equation for charge time and current

Answer 4

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

Question 4

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

Answer 4

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

Question 4

what are some places you may see leds being used

Answer 4

traffic lights
alarm clocks
led bulbs

Question 5

how are ammeters connected

Answer 5

in series

Question 5

how are voltmeters connected

Answer 5

in paralell

Question 5

what are ldrs and thermistors

Answer 5

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

Question 6

what does the difference between series and parallel circuits change

Answer 6

the way we measure current , voltage and resistance

Question 7

what are the negatives of series circuits

Answer 7

if 1 component is disconnected the whole series stops working

the pd is shared across all components

Question 8

what is the total resistance of a circuit in series

Answer 8

the sum of each individuals resistance

Question 9

do ammeters have resistance

Answer 9

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

Question 10

even if voltmeters are in parallel in a series circuit

Answer 10

we still treat the circuit in series

Question 11

why would a component have a higher share of the voltage

Answer 11

if it had a greater resistance

Question 12

what are the benefits of the multiple loops of parallel circuits

Answer 12

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

Question 13

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

Answer 13

every component will have 12v across them

Question 14

what is difference in current in parallel vs series

Answer 14

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

Question 15

what is the difference in pd

Answer 15

series-split between components parallel-same across all components

Question 16

what is the difference in resistance

Answer 16

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

Question 17

what is the equation for power/pd /current

Answer 17

power or energy transferred in joules = pd x current

Question 18

what is the national grid

Answer 18

giant network of transformers and wires that distribute our electricity

Question 19

when does electricity demand peak in

Answer 19

the late evening and afternoon

Question 20

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

Answer 20

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

Question 21

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

Answer 21

voltage must be high and current must be very low

Question 22

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

Answer 22

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

Question 23

what is the journey of electricity in the national grid

Answer 23

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

Question 24

why do we use step down transformers

Answer 24

they lower voltage and increase current making it safe to use

Question 25

what are the 2 types of current

Answer 25

alternating and direct

Question 26

what makes alternating current alternating and how do we get it

Answer 26

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

Question 27

what is the current in the uk and frequency

Answer 27

alternating at 50hz frequency

Question 28

what does the frequency being 50hz mean

Answer 28

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

Question 29

what is direct current

Answer 29

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

Question 30

what are some items that run on direct current

Answer 30

cells and batteries in phone or calculator

Question 31

what does an oscilloscope do

Answer 31

show how voltage changes with time

Question 32

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

Answer 32

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

Question 33

what colour is the live wire and what does it do

Answer 33

brown provides alternating pd from mains supply

Question 34

what colour is the neutral wire and what does it do

Answer 34

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

Question 35

what colour is the earth wire and what does it do

Answer 35

it is striped green and yellow has pd of 0v stops appliance casing becoming live providing alternative pathway for current to flow away

Question 36

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

Answer 36

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

Question 37

why can we not touch the live wire

Answer 37

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

Question 38

what is a risk in using electricity

Answer 38

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

Question 39

what are fuses

Answer 39

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

Question 40

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

Answer 40

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

Question 41

what are the pros and cons of fuses

Answer 41

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

Question 42

explain circuit breakers +advantages and disadvantages over fuses

Answer 42

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

Question 43

how do we stop electric shocks

Answer 43

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

Question 44

what are used against surges of current

Answer 44

fuses and circuit breakers

Question 45

what is the rating of a fuse

Answer 45

current that causes fuse to break circuit

Question 46

what is static electricity

Answer 46

build up of charge on insulating materials

Question 47

what is the only thing transferred in static electricity

Answer 47

electrons

Question 48

what happens when an object gains more and more electrons

Answer 48

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

Question 49

why cant 2 conducting materials build up charge

Answer 49

friction between them would cause the electrons to flow straight back

Question 51

For electrons to flow what must happen

Answer 51

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