Basic ideas…Basic ideas…Electric current is when electrons start to flow around acircuit. We use an _________ to measure it and it ismeasured in ____.Potential difference (also called _______) is how big thepush on the electrons is. We use a ________ to measureit and it is measured in ______.Resistance is anything that resists an electric current. Itis measured in _____.”(Words: volts, amps, ohms, voltage, ammeter, voltmeter)
More basic ideas…More basic ideas…If a battery isadded the currentwill ________because there is agreater _____ onthe electronsIf a bulb is addedthe current will_______ becausethere is greater________ in thecircuit
Current in a series circuitCurrent in a series circuitIf the currenthere is 2amps…Thecurrenthere willbe…The currenthere willbe…And thecurrenthere willbe…In other words, the current in a seriescircuit is THE SAME at any point
Current in a parallel circuitCurrent in a parallel circuitA PARALLEL circuit is one where the current has a “choiceof routes”Here comes the current…And the rest willgo down here…Half of the currentwill go down here(assuming the bulbsare the same)…
Current in a parallel circuitCurrent in a parallel circuitIf thecurrenthere is 6ampsThe currenthere will be…The currenthere will be…The currenthere will be…And thecurrent herewill be…
Voltage in a series circuitVoltage in a series circuitVV VIf the voltageacross thebattery is 6V……and thesebulbs are allidentical……what will thevoltage acrosseach bulb be? 2V
Voltage in a series circuitVoltage in a series circuitVVIf the voltageacross thebattery is 6V……what will thevoltage acrosstwo bulbs be?4V
Voltage in a parallel circuitVoltage in a parallel circuitIf the voltage acrossthe batteries is 4V…What is thevoltage here?And here?VV4V4V
SummarySummaryIn a SERIES circuit:Current is THE SAME at any pointVoltage SPLITS UP over each componentIn a PARALLEL circuit:Current SPLITS UP down each “strand”Voltage is THE SAME across each”strand”
An example question:An example question:V1V26V3AA1A2V3A3
Advantages of parallel circuits…Advantages of parallel circuits…There are two main reasons why parallel circuits are usedmore commonly than series circuits:1) Extra appliances (like bulbs) can be added withoutaffecting the output of the others2) If one appliance breaks it won’t affect the otherseither
Georg Simon Ohm1789-1854ResistanceResistanceResistance is anything that willRESIST a current. It is measuredin Ohms, a unit named after me.The resistance of a component can becalculated using Ohm’s Law:Resistance = Voltage (in V)(in Ω) Current (in A)VRI
An example question:An example question:VA1) What is the resistance acrossthis bulb?2) Assuming all the bulbs are thesame what is the total resistancein this circuit?Voltmeterreads 10VAmmeterreads 2A
Current-voltage graphsCurrent-voltage graphsIVIVIV1. Resistor 3. Diode2. BulbExplain the shape of each graph
Three simple components:Three simple components:1) Diode – only lets current flow in one direction2) Light dependant resistor – resistance DECREASES whenlight intensity INCREASES3) Thermistor – resistance DECREASES when temperatureINCREASES
DC and ACDC and ACDC stands for “DirectCurrent” – the current onlyflows in one direction:AC stands for “AlternatingCurrent” – the currentchanges direction 50 timesevery second (frequency =50Hz)1/50ths240VVVTimeT
FusesFusesFuses are _______ devices. Ifthere is a fault in an appliancewhich causes the ____ andneutral (or earth) wire to crossthen a ______ current will flowthrough the _____ and cause itto _____. This will break the_______ and protect theappliance and user from further_____.Words – large, harm, safety, melt, live, circuit, fuse
Circuit breakersCircuit breakersIf the current becomes too high the __________ isactivated. This will ______ the iron and the contact willbe _______. This will break the circuit.Circuit breakers have two main advantages over fuses:they work ______ and can easily be ______.Words – electromagnet, broken, attract, reset, quicker
Earth wiresEarth wiresEarth wires are always used if an appliance has a _____case. If there is a _____ in the appliance, causing the livewire to ______ the case, the current “_______” down theearth wire and the ______ blows.Words – fuse, fault, metal, surges, touch
Power and fusesPower and fusesPower is “the rate of doing work”.The amount of power being used inan electrical circuit is given by: PIVPower = voltage x currentin W in V in AUsing this equation we can work out the fuse rating for anyappliance. For example, a 3kW (3000W) fire plugged into a240V supply would need a current of _______ A, so a_______ amp fuse would be used (fuse values are usually3, 5 or 13A).
Power and fusesPower and fusesCopy and complete the following table:Appliance Power rating(W)Voltage (V) Currentneeded (A)Fuse needed(3, 5 or 13A)Toaster 720 240Fire 2000 240Hairdryer 300 240Hoover 1000 240Computer 100 240Stereo 80 240
Charge (Q)Charge (Q)As we said, electricity is when electrons move around acircuit and carry energy with them. Each electron has anegative CHARGE. Charge is measured in Coulombs (C).We can work out how much charge flows in a circuit usingthe equation:QTICharge = current x time(in C) (in A) (in s)
Example questionsExample questionsCharge (C) Current (A) Time (s)5 20.4 120 0.550 2503 601) A circuit is switched on for 30s with a current of 3A. How muchcharge flowed?2) During electrolysis 6A was passed through some copper chlorideand a charge of 1200C flowed. How long was the experiment onfor?3) A bed lamp is switched on for 10 minutes. It works on a current of0.5A. How much charge flowed?
Energy and chargeEnergy and chargeThe amount of energy that flows in a circuit will depend onthe amount of charge carried by the electrons and thevoltage pushing the charge around:EQVEnergy transferred = charge x voltage(in J) (in C) (in V)
Example questionsExample questions1) In a radio circuit a voltage of 6V is applied and a chargeof 100C flows. How much energy has been transferred?2) In this circuit the radio drew a current of 0.5A. Howlong was it on for?3) A motor operates at 6V and draws a current of 3A. Themotor is used for 5 minutes. Calculate: a) The motor’sresistance, b) the charge flowing through it, c) theenergy supplied to it4) A lamp is attached to a 12V circuit and a charge of1200C flows through it. If the lamp is on for 10 minutescalculate a) the current, b) the resistance, c) theenergy supplied to the bulb.
Comparing magnets and solenoidsComparing magnets and solenoidsN SMagnet:Solenoid:
ElectromagnetsElectromagnetsThe strength of an electromagnet can be increased bydoing three things:1) Increasing the voltage2) Increasing the number of coils3) Inserting an iron core(The poles can be reversed byreversing the direction of the current)
ElectromagneticElectromagneticinductioninductionThe direction of the inducedcurrent is reversed if…1) The magnet is moved in theopposite direction2) The other pole is insertedfirst
ElectromagneticElectromagneticinductioninductionThe size of the induced currentcan be increased by:1) Increasing the speed ofmovement2) Increasing the magnetstrength3) Increasing the number ofturns on the coil
AC GeneratorAC GeneratorInduced current can be increased in 4 ways:1) Increasing the speed of movement2) Increasing the magnetic field strength3) Increasing the number of turns on the coil4) Increasing the are of the coil
The National GridThe National GridElectricity reaches our homes from power stations through theNational Grid:If electricity companies transmitted electricity at 240 volts throughoverhead power lines there would be too much ______ loss by the timeelectricity reaches our homes. This is because the current is ___. Toovercome this they use devices called transformers to “step up” thevoltage onto the power lines. They then “____ ____” the voltage atthe end of the power lines before it reaches our homes. This way thevoltage is _____ and the current and power loss are both ____.Power stationStep uptransformerStep downtransformerHomesWords – step down, high, power, low, high
TransformersTransformersTransformers are used to _____ __ or step down_______. They only work on AC because an ________current in the primary coil causes a constantly alternating_______ ______. This will “_____” an alternatingcurrent in the secondary coil.Voltage across primary (Vp)No. of turns on secondary (Ns)Voltage across secondary (Vs)No. of turns on primary (Np)Words – alternating, magnetic field, induce, step up, voltageWe can work out how much a transformer will step up orstep down a voltage:
Static electricityStatic electricityStatic electricity is when charge “build up” on an objectand doesn’t move, e.g. rubbing a rod:
Two differentrods willattract eachother if theyhave differentcharge:Two rodsmade of thesame materialwill repel eachother due tohaving thesame charge:
Van de Graff generatorsVan de Graff generatorsA charge builds up onthe dome due toelectrons being “______off” by the belt. If abig enough ______ isbuilt up then the voltagebecomes high enough to_____ the air moleculesand the electrons “___”down to Earth – this isan electric _________.Words – charge, jump,current, rubbed, ionise
Use of static 1 - PhotocopiersUse of static 1 - PhotocopiersPhotocopiers use staticelectricity. They work by: 1)Copying an ______ of the pageonto a ______ plate, 2) Lightthen causes the charge to ____away, leaving an “electrostaticimpression” of the page, 3) Thecharges left on the plate______ small drops of blackpowder, 4) The powder istransferred from the plate ontothe _____, 5) The paper is_____ to “fix” the powder.Words – heated, leak, paper, image, charged, attract
Use of static 2 - PrintersUse of static 2 - PrintersInkjet printers work by spraying charged drops of inkonto a page. The droplets can be directed using twooppositely charged plates. The voltage on these platescan be easily swapped or varied. The inkjet cartridgecan also moved across the page by the printer
Dangers of staticDangers of staticDuring refuelling the fuel gains electrons from the pipe,making the pipe positive and the fuel negative. Theresulting voltage may cause a spark – bad news!Solution: Either earth the fuel tank with a copper rod orconnect the tanker to the plane by a copper conductor.
ElectrolysisElectrolysisElectrolysis is used to extract a HIGHLY REACTIVE metal.= chloride ion= copper ionWhen we electrolysedcopper chloride thenegative chloride ionsmoved to the positiveelectrode and the positivecopper ions moved to thenegative electrode –OPPOSITES ATTRACT!!!
QuestionsQuestions1) A current of 2A flows through some copper chloride for 1 minuteand 0.01g of copper is deposited at the negative electrode.a) How much would be deposited if the current was increased to6A?b) How much would be deposited if the current was kept at 6A andthe experiment was left for another minute?c) How much charge flowed in question (b) above?2) A current of 0.05A flows through some copper chloride for 500seconds and 0.05g of chlorine is released at the positive electrode.a) How much would be deposited if the current was increased to0.1A?b) How much would be deposited if the current was kept at 0.1Aand the experiment was left for 250 seconds instead?c) How much charge flowed in question (b) above?