electricity

current is the rate of flow of charge round the circuit

what is current?

electrons usually carry the charge- they’re negatively charged particles

what carries the charge through the circuit?

current will only flow through a component if there is a voltage across that component

what is the one thing needed for currently to flow through a component?

voltage is the energy transferred per unit charge passed and the volt is a joule per coulomb

voltage is also know as potential difference or p.d

what is voltage?

resistance is anything in the circuit that slows the flow.

what is resistance?

there will be a higher resistance

if you add more components to the circuit what will happen to the resistance

ampere (amp) A

what is the unit for current?

volts V

what is the unit for voltage?

ohms

what is the unit for resistance?

more current

if you increase the voltage what will happen to the current?

less current and more voltage to keeps the same current flowing

if you increase the resistance what will happen to the current?

an ammeter measure the current in amps flowing through the components

an ammeter must be placed in series anywhere in the main circuit but never in parallel like the voltmeter

wha is an ammeter?

a voltmeter measures the voltage in volts across the component

must be place in parallel

what is a voltmeter?

a.c

what is the name for main supply?

d.c

what is the name for battery supply?

approx 230 volts

what is the uk main electricity supply?

an a.c supply means alternating current which means the current is constantly changing direction

what is an a.c supply?

d.c is direct current which supply cell and battery and current flows in same direction.

what is d.c?

what is the formula for voltage?

shows you how the resistance of the component behave.

the steeper the graph the lower the resistance

what does the gradient of an I-V graph show you?

a straight line graph has a constant gradient and shows a constant resistance.

if the graph curves it means the resistance is changing.

what does a straight line graph shows you?

the current through a wire at a constant temperature is proportional to voltage

what is the graph for a wire?

the current through a resistor at a constant temperature is proportional to voltage.

different resistors have different resistances hence the different slopes.

what is the graph for different resistors?

as the temperature of the lamp increase the resistance increases hence the curve

what is the graph for metal filament lamp?

current will only flow through a diode in one direction

what is the graph for diode?

circuit symbol- cell?

circuit symbol- battery?

circuit symbol- switch open?

circuit symbol- switch closed?

circuit symbol- fuse/circuit breaker?

circuit symbol- filament lamp?

circuit symbol- LED?

circuit symbol- motor?

circuit symbol- heater?

circuit symbol- generator?

circuit symbol- fixed resistor?

circuit symbol- variable resistor?

circuit symbol- ammeter?

circuit symbol- voltmeter?

circuit symbol- diode?

circuit symbol- LDR?

circuit symbol- thermistor?

circuit symbol- relay?

light-emitting diodes:

* emit light when a current flows through them in the forward direction
* used for the numbers on digital clocks, traffic lights and in remote controls
* they don’t have a filament that can burn out

what are LED’s?

a light dependant resistor is a special type of resistor that changes its resistance depending on how much light falls on it.

in bright light resistant falls

in dark light resistance is highest

LDR’s are great for electronic circuits and burglar detectors

what is an LDR?

a thermistor is a temperature dependant resistor

in hot condition resistance decreases

in cold condition resistance increases

thermistor are useful in temperature detectors such as car engine temperature sensors, thermostats and fire alarms

what is a thermistor?

* different components are connected in a line end to end from positive to negative expect for voltmeter as it is in parallel
* if you remove a component the circuit is broken
* this is not good for example fairy light

what happens in a series circuit?

* bigger supply p.d when more cells are in series
* current is the same everywhere
* total p.d of the supply is shared between components
* the p.d for each component depends on its resistance
* total resistance of the circuit depends on the number of components and the type of the components used

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what happens to p.d, current and resistance in series?

* each components is separately connected to the +ve and -ve of the supply
* if you remove a component circuit still works

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what happens in parallel circuit?

* p.d is the same across all branches
* current is shared between branches
* total current flowing around the circuit = to the total of all the currents through the separate component
* the current through a branch depends on the resistance of the branch
* the higher the resistance the harder it is for charge to flow
* total resistance decrease if second resistor is added in parallel

what happens to p.d, current and resistance in parallel ?

what is the formula relating charge current and time?

it transfers energy

* energy is supplied to the charge at the power source
* the charge gives up this energy when it falls thought any voltage drop in components
* the bigger the change in voltage the more energy is transferred
* a battery with a bigger voltage will supply more energy to the circuit for every coulomb of charge h

what happens when a charge drops through a voltage?

energy transferred = charge x voltage

energy transferred = charge x current x resistance

what are the 2 formulas for energy transferred?

live, neutral and earth

what are the 3 wires in a plug?

only live and neutral are usually needed but if something goes wrong the earth wire stops you from getting hurt

which 2 wires are mostly needed?

the live wire alternates between a HIGH +VE AND -VE VOLTAGE of 230v

what does the live wire alternate?

0V

what is the voltage for neutral wire?

through the live wire and the neutral wire

which 2 wires does electricity flow through?

for safety and they work together

what is the earth/fuse/circuit breaker for?

plug labelled with wires

must be ‘earthed’ to reduce the danger of electric shock.

must be attached to an earth wire

earthed conductor can never become live

what do all appliances with metal cases must have?

means that if the appliance has a plastic casing and no metal parts are showing

plastics are an insulator so it stops a current flowing.

anything with double insulation doesn’t need an earth wire- just a live and neutral

what does double insulated mean?

prevent fires and shock.

what do earthing and fuses prevent?

the case is earthed so a big current flows through the live wire, the case and the earth wire

if a fault develops in which the live wire touches the metal case what happens?

the surge in current blows and melts the fuse which cuts of the live supply.

this isolates the whole appliance making it impossible to get an electric shock .

prevents the risk of fire caused by the heating effect of a large current

what does the surge in the current do?

Circuit breakers are an electric safety device used in some circuits.

like fuses they protect the circuit from damage if too much current flow.

what are circuit breakers?

they break the circuit by opening a switch.

what happens when circuit breakers detect a surge in current in a circuit?

when an electric current passes through them.

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when do resistors get hot?

* electrons collide with ion in the lattice that makes up the resistor
* this gives ions energy which causes them to vibrate and heat up
* heating effect increases resistor resistance
* less current greater voltage
* heating effect causes components in the circuit to melt circuit will stop working
* the circuit will melt and break if the current gets to high.

how do the resistor get hot?

electrical power is the rate at which an appliances transfers energy

what is electric power?

transfers a lot of energy in a short time.

an appliances with a high power rating transfers what?

watts W

what is power measured in? formula

electrically

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how do electrical appliances transfer energy? formula

like charges repel opposite charge attract

what do like charges do?

conductors conduct charge insulators don’t

conductors are usually metal like copper and silver

insulators example like plastic and rubber

what do conductors do?

friction

what causes static charges?

* polythene and acetate rods being rubbed with a cloth duster
* electrons move from the duster to the rod
* rod becomes negatively charged and the duster is left with an = positive charge
* when acetate rod is rubber electrons move from the rude to the duster
* duster becomes -ve and rod has =+ve

investigation of static electricity?

* you can see where a material is charged by using a gold leaf electroscope
* a gold leaf electroscope has a metal disc connected to the metal rod at the bottom of which are attached 2 thin pieces of gold leaf
* when a road with a charge is brought near the disc electrons will either attract or repel depending on the charge
* both gold leafs will have the same charge so they will repel each other causing them to rise
* when the rod is taken away the gold leaves will discharge and fall again

gold leaf electroscope experiment?

* suspend a road with a know charge on a thread and see if there is a repulsion or attraction when the rod you’re testing is brought close to it
* if there is an attraction then the test road has the opposite charge to the suspended rod
* if there is a repulsion then the test rod has the same charge as the suspended rod

suspending a charged rod experiment

a van de Graaff generator is sued to demonstrate electrostatic charge.

made of a rubber melt moving round plastic rollers underneath a metal dome

an electrostatic charge is built up.

the human body conducts charge like charges repel so the charges will spread out through your body and makes your hair stand up

what is a van de graaff?

* tiny droplets of ink are forced out of a fine nozzle making them electrically charged
* the droplets are deflected as they pass between 2 metal plates
* a voltage is applied to the plates one negative and one positive
* the droplets are attracted to the plate of the opposite charge and repelled from the plate with the same charge
* the size and direction of the voltage across each plate change so each droplet is deflected to hit a different place on the paper
* lots of tiny dots make up your printout

what happens an inkjet printer?

* the image plate is positively charged. an image of what you’re copying is projected onto it.
* whiter bits of what your copying make light fall on the plate and the charge leaks away in those places
* the charged bits attract negatively charged black powder which is transferred onto positively charged paper
* the paper is heating so the powder sticks
* and there is a photocopy

what happens in a photocopier?

when synthetic clothes are dragged over each other or over your heat electrons get scraped off leaving static charges on both parts which leads to the attraction and they stick together. little sparks and shock form as the charges rearrange themselves.

what happens when clothing crackles?

rain drops and ice bump together inside storm clouds knocking offf electrons and leaving the top of the cloud positively charged and the bottom of the cloud negative.

this creates a huge voltage and a big spark

what happens in lightning?

as fuel flows out of of a filler pipe static can build up

this can easily lead to a spark and in dusty or fumy places

so do risk the hazard of a BOOM they make the nozzles out of metal so that the charge is conducted away instead of building up

there are also earthing straps between the fuel tank and the fuel pipe

what happens when someone is putting fuel in?