P2-Electricity Flashcards
What is potential difference
Is the driving force that pushes the charge around
what is resistance
Is something that slows the flow down
What does the current flowing through a component to depend on
Depends on the potential difference across it and the resistance of the component
The greater the resistance across a component the smaller the current that flows
What are ammeters
Measures the current flowing through the test wire
The Ammeter must always be placed in series with whatever you’re investigating
What is a voltmeter
measures the potential difference across the test wire
The voltmeter must always be placed in parallel around whatever you’re investigating
Why is the IV characteristic of an ohmic conductor like that
For some components as the current through them is charged the resistance of the component changes as well
The resistance of ohmic conductor doesn’t change with the current. At a constant temperature of the current flowing through this is directly proportional to the potential difference across it
Why is the IV characteristic of a filament lamp like that
When an electrical charge flows through a filament lamp it’s transfers enough energy to the thermal energy store of the filament lamp which is designed to heat up. Resistance increases with temperature so as the current increases the filament lamp heats up more and the resistance increases
Why is the IV characteristic of a Diode like that
For diode the resistance depends on the direction of the current. They will happily let current flow in One Direction but have a very high resistance if it is reversed
What does the IV graph for an ohmic conductor look like
It goes diagonally across the whole graph through the second and third quarters
What does the IV graph for an filament lamp look like
This is a Bendy line through the second and third quarters
What does the IV graph for an diode look like
This is a line increasing is deeply in the second quarter
What is an LDR
This is the shorthand for light dependent resistor
An LDR is an resistor that is dependent on the intensity of light
The brightest light the resistance falls
The darkest resistance is highest
They have loads of applications including automatic night lights, outdoor lighting and burglar detectors
What is an Thermistor
This is a temperature dependent resistor
In hot conditions the resistance drops
In cool conditions the resistance goes up
Thermistors make use for temperature detectors
Water sensing circuits
Sensing circuits can be used to turn on or increase the power to components depending on the conditions that they are in
What are series circuits
In a series circuits, the different components are are connected in a line, end to end
If you remove or disconnect one component, the circuit is broken and they all stop. This is generally not very handy and in practice very few things are connected in series
What is the potential difference like in a series circuits
In series circuits the total potential difference of the supply is shared between the various components. So the potential difference around a series circuit which adds up to equal to source potential difference
What’s the current like in a series circuit
In series circuit the current flows through all components
The size of the current is determined by the total potential difference of the cells and the total resistance of the circuit
What’s the resistance like in a series circuit
In series circuits the total resistance of two components it’s just that some of the resistances
This is because by adding a resistor in series the two resistors have to share the total potential difference
The bigger components resistance the bigger share of the total potential difference
What is a parallel circuit
In Parallel circuits each component is separately connected to the supply
If you remove or disconnect one of them it will hardly affect the others at all
This is obviously how most things must be connected. For example in cars and in household electrics. You have to be able to switch everything on and off
Every day circuits often include a mixture of series and parallel parts
What is the potential difference like in a parallel circuit
In parallel circuit components get the full source potential difference, so the potential difference is the same across all components
This means that I don’t have boobs connected in parallel will all have the same brightness
What is the current like in a parallel circuit
In parallel circuits the total current flowing around the circuit is equal to the total of all the Currents through the separate components
In a parallel circuit there are junctions with the current either splits all rejoins. The total current going into a junction has to equal the total current leaving
If two identical components are connected in parallel then the same current will flow through each component
Why does adding a resistor in parallel reduced the total resistance
In parallel by three sisters have the same potential difference across them as the source
This means the pushing force making the current flow is the same as the source potential difference for each resistor that you add
But by adding another loop the current had more than one direction to go in
This increases the total current that can throw around the circuit. An increase in current means a decrease in the total resistance of the circuit
what are the 2 type of electricity supply
alternating current (ac)
direct current (dc)
what are alternating current supplies
the current is constantly changing direction. they are produced by alternating voltages in which the positive and negative ends keep alternating
what are direct current supplies
is a current that is always flowing in the same direction. it is created by a direct voltage
what voltage is the UK mains supply
is an ac supply at around 230V
what is the frequency of an ac mains supply
50 cycles per second or 50Hz
what is an example of dc supply
cells and batteries
what is the meaning of 3 core cables
this means that that they have 3 wires inside them each with a core of copper and coloured plastic coating
the colour of the coating shows it purpose
the colours are always the same for all appliances
what is the brown wire
Live wire
The brown wire produces the alternating potential difference at about 230V from the mains supply
what is the blue wire
Neutral wire
the neutral wire completes the circuit and carries away the current
electricity normally flows in through the live wire and out through the neutral
it is around 0V
what is the green and yellow wire
It is for protecting the wiring and for safety
it stops the appliance casing from becoming live
it doesn’t usually carry a current but only when there is a fault
it also at 0V
how does the live wire give you an electric
your body live the earth is at 0V. this means that if you touch the live wire , a large potential difference is produced across your body and a current flows through you
This causes a large electric shock which could injure or even kill you
even if something is off there is a chance of getting an electric shock because there is a potential difference in the live wire
any connection between live and earth can be dangerous. if they link it creates a low resistance path to earth a huge current will flow, which could result in a fire
why is potential difference the energy transferred per charge passed
when an electric al charge goes through a change in potential difference, then energy is transferred
Energy is supplied to the charge at the power source to ‘rise’ it through a potential
the charge gives up this energy when it falls through any potential drop in components elsewhere in the circuit
that means that a buttery with a bigger pd will supply more energy to the circuit for every coulomb of charge which flows round it because the charge is raised up ‘higher’ at the start
how is electricity distributed in the uk
this is done by using the national grid
the notional grid is a giant system of cables and transformers that cover the uk and connects power stations to consumers
the national grid transfers electrical power from power station anywhere on the grid to anywhere else on the grid where it is needed
when and how does electricity production meet demand
throughout the day, electricity usage changes. power stations have to produce enough electricity for everyone to have when they need
they can predict when the most electricity will be used though. demand increases when people get up in the morning, come home form school or work and when it starts to get dark or cold
power stations often run at well below their maximum power output
What sort of potential difference and current do the National Grid use
To transmit the huge amount of power needed you need a high potential difference or a high current
The problem with a high current is that you lose loads of energy as the wires heat up and energy is transferred to the thermal energy store of the surroundings
It’s much cheaper to boost the potential difference up really high (400,000 V) and keep the current as low as possible
For a greater power, increasing the potential difference decreases the current and, which decreases the energy lost by heating the wires and the surroundings. This makes the National Grid an affective way of transferring energy
How is the potential difference changed in the National Grid
To get the potential difference to 400,000 V to transmit power requires transformers as well as big pylons with a huge installation-but it’s still cheaper
The transformers have to step the potential difference up at one end for efficient transmission and then take it back down to safe, usable levels at the other end
The potential difference is increased (steped up) using a step up transformer
It’s then reduced again (stepped down) for domestic use using a stepdown transformer
