2 - electricity Flashcards
what is electrical current
- the flow of electrical charge
- can only flow round a closed circuit if there is potential difference
- in a single loop the current is the same everywhere
what is potential difference
- the force that pushes charge around
what is resistance
- anything that slows the flow down
ammeter
- measure CURRENT flowing through test wire
- SERIES circuit
voltmeter
- meaures the PD flowing through test wire
- must be in a PARALLEL circuit
investigating factors affecting resistance practical
- attach crocodile clip to wire - level to 0cm on ruler
- attach 2nd crocodile clip to 10 cm
- close switch and measure the current and pd
- open and move 2nd clip to 20cm and close and record again
- repeat
- plot on graph and use the pd and current to work out resistance and then put it against length of wire
LRD in bright and dark light and uses
- dependent on the intensity of light
- bright lights —> resistance falls
- darkness —> resistance is highest
- can be used in burglar alarms
thermistor in hot and cold places and uses
- dependent on the tmperature
- hot —> resistance drops
- cold —> resistance rises
- can be used as thermostats
series circuits
- if you remove one component - everything will stop
- current is the same everywhere I1 = I2 = I3
- the potential difference is shared Total = R1 + R2 + R3..,
- the total resistance is the sum of the componants
parallel circuits
- if you remove one thing it wont effect the other components
- all componants have a full source of pd V1 = V2 = V3
- current is shared Itotal = I1 + I2 + I3 …
what happens if you add a resistor to a parallel circuit
- reduces the total resistance
ohmic conductor graph
current is directly proportional to the potential difference at a constant temp
- straight line through the graph
- i on the y axis
- v on the x axis
filament lamp graph
as the current increases the temp of lamp increases so the resistance increases because the particles vibrate more and therefore collide more with the current
- curved graph
diode graph
current only flows in one direction and then the current suddenly increase - like a plank of wood snapping
graph starts flat and then increases
I-v characteristics
- ohmic conductor
- filament lamp
- diode
sensing circuits
used to turn on or increase the power to certain components in a circuit depending on the conditions that the circuit is operating in.
ac
- alternating pd used creates an alternating current - fluctuates between positive and negative
- this means direction that charge is flowing is constantly flowing back and forth
dc
- produced by a direct potential difference
- either positive or negative the whole time
- so charge is always flowing in the same direction
- found in cells/ batteries eg phone or caluclator
live wire
- brown
- provides the alternating potential dofference from the mian supply
- 230 V
neutral wire
- blue
- completes the circuit by being covered in blue pastic
- 0V
earth wire
- yellow and green
- provides a low resistance path to the ground. In the event of a fault, the live current passing through the case will follow this path to the ground instead of passing through a person.
- 0V
how do you get an electric shock
- your body is at 0V
- if you touch LIVE wire a potential differnece is prduced across your body
- and then current flows through you - electric shock
whats the National grid
- giant system of cables and transformers
- transfers electrical power from power stations anywhere on the grid to anywhere its needed
what pd and current does the national grid use
- really high pd
- really low current (if current is too high then the thermal energy will be lost into surroundings)
transformers
have a primary and secondary coil joined with an iron core
step up and step down transformers
step up -> increases pd = more turns in secondary coil
step down -> reduces pd = more turns in primary
how does friction cause static
- when insulating materials are rubbed
- neg charged electrons are scraped off one and onto the other
- makes the materials electrically charged with a positive static charge on one and an equal negative static charge on the other
- ONLY ELECTRONS MOVE
how is a spark caused
- as electric charge builds up the PD increases between earth object 0v and charged object
- high PD causes a strong electrical field
- this causes air particles to be removed
- then when current flows - SPARK
UK AC mains supply - pd and frequency
230 V
50 HZ
- therefore the pd and current fluctuate between +230v and -230v, 50 times per second
