electricity Flashcards
what is an electrical circuit
a closed loop with a battery or cell and something for electrons to flow through
what is the current
measure of flow of electrons around the circuit-(amps)A
it is like the water flowing through a hose
what is pd/voltage
force driving the flow of electron provided by cell or battery (V)
-pump that forces water along the pipe
what is resistance
anything that resists or opposes the flow of electrons(Ohms)
-similar to a partial blockage in pipe
what are the terminals
positive and negative the longer being positive
-current flows from positive to negative terminal as electrons are attracted to the oppositely charged positive terminal
what is v=ir
pd = current x resistance
what is the relationship between voltage and current if resistance is constant
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)
what is the relationship of current and voltage with a filament lamp
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
what is the relation between a diode current and resistance
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
what does it mean when the resistance is constant (fixed resistor)but the voltage and current are negative
the battery is attached the opposite way
for wires and resistors what and why will increasing the temp do
ions in the metal vibrate faster making it harder for electrons pass along the wire essentially increasing the resistance
what is charge
the measure of the total current that flowed over a certain period of time(Q) measured in coulombs(C)
what is the equation for charge time and current
Q(C)=I(A) x t(s)
what are the role of fuses in a circuit.what is the symbol
break if too much current flows through a circuit.
the symbol is a rectangle with a line straight through it
what are some places you may see leds being used
traffic lights
alarm clocks
led bulbs
how are ammeters connected
in series
how are voltmeters connected
in paralell
what are ldrs and thermistors
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
what does the difference between series and parallel circuits change
the way we measure current , voltage and resistance
what are the negatives of series circuits
if 1 component is disconnected the whole series stops working
the pd is shared across all components
what is the total resistance of a circuit in series
the sum of each individuals resistance
do ammeters have resistance
yes but it is so tiny we can ignore them in our calculations
even if voltmeters are in parallel in a series circuit
we still treat the circuit in series
why would a component have a higher share of the voltage
if it had a greater resistance
what are the benefits of the multiple loops of parallel circuits
if a particular component break is still intact the overall circuit a
in parallel circuits what happens i f the pd is 12v
every component will have 12v across them
what is difference in current in parallel vs series
in series-current is= across all components
in parallel i1=i2+i3
what is the difference in pd
series-split between components
parallel-same across all components
what is the difference in resistance
series-sum of all resistance
parallel-less than value of resistance over components
what is the equation for power/pd /current
power or energy transferred in joules = pd x current
what is the national grid
giant network of transformers and wires that distribute our electricity
when does electricity demand peak in
the late evening and afternoon
what does national grid have to transmit and what factors does this limit
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
how do we avoid get lots of power without wasting a lot of energy
voltage must be high and current must be very low
what and why do we use to make the voltage really high in the national grid
step up transformers which increase voltage to about 400000v to minimise energy loss and decrease current
what is the journey of electricity in the national grid
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
why do we use step down transformers
they lower voltage and increase current making it safe to use
what are the 2 types of current
alternating and direct
what makes alternating current alternating and how do we get it
when the current changes direction constantly by using an alternating pd that switches from positive and negative
what is the current in the uk and frequency
alternating at 50hz frequency
what does the frequency being 50hz mean
the voltage will go from +240v to -240v 50 times every second and so will the current
what is direct current
produced by pd which is either positive or negative and never changes direction
what are some items that run on direct current
cells and batteries in phone or calculator
what does an oscilloscope do
show how voltage changes with time
what are the 3 wires in the 3 core cable and what do they all have
live
neutral
earth
they are made of copper so they can conduct electricity and coated in a layer of insulating plastic for safety
what colour is the live wire and what does it do
brown
provides alternating pd from mains supply
what colour is the neutral wire and what does it do
blue
it completes the circuit by carrying away current(has a pd of 0)
what colour is the earth wire and what does it do
it is striped green and yellow
has pd of 0v
stops appliance casing becoming live providing alternative pathway for current to flow away
what do the pd of 0v for the earth and neutral wire help do
difference in voltage from the live wire is what causes electricity to pass from one to another
why can we not touch the live wire
as we have 0 pd and it would cause a large current to flow through us as an electric shock
what is a risk in using electricity
surges of current(from change in circuits or faults in circuit or appliance)which can cause fires or electric shocks or damage appliances
what are fuses
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
what should a fuse be compared to the rating of ur appliance
a few amps above
eg if a toaster has a 10a get a 13a so it only stops it at 13a
what are the pros and cons of fuses
pros
-simple and cheap
cons
-permanently broken after single surge
explain circuit breakers +advantages and disadvantages over fuses
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
how do we stop electric shocks
-earthing
-double insulate appliance (cover in plastic(doesnt conduct electricity) casing so there is no exposed metal
this doesnt need an earth wire
what are used against surges of current
fuses and circuit breakers
what is the rating of a fuse
current that causes fuse to break circuit
what is static electricity
build up of charge on insulating materials
what is the only thing transferred in static electricity
electrons
what happens when an object gains more and more electrons
a pd between charged object and earthed object and if pd gets large enough the electrons will jump across causing a spark
why cant 2 conducting materials build up charge
friction between them would cause the electrons to flow straight back
For electrons to flow what must happen
Circuit must be closed
Must be source of pd(battery or cell)
