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Static Electricity Some insulating materials become electrically charged when they are rubbed together When you rub two different insulating materials against each other they become electrically charged Negatively charged electrons will be scraped off on and onto the other It will leave a positive charge on one and on a negative charge on the other The material that loses electrons becomes positively charged The material that gains electrons becomes negatively charged Which way the electrons are transferred are depends on the 2 materials used Both materials gain an equal amount of charge, but the charges are opposite Charges that are the same repel, while unlike charges attract When they are brought together they exert a force on one another The forces get weaker the further apart the objects are This only works for insulated objects Electrical charges move easily to earth through conductors such as metals (they have free electrons)

Only the electrons moveThis will only cause positive or negative chargesProduced by the movement of electronsPositive charges don't move

CurrentThe flow of electric charge round a circuitNo current can flow if the circuit is broken - for example, when a switch is openCurrent will only flow through a component if there is a potential differenceUnit = ampere, A

Potential DifferenceThe driving force that pushes the current aroundalso called voltageCells or batteries often provide the potential difference neededUnit = volt, V

More charge passes around the circuit when a bigger current flows

The potential difference is the work done per coulomb of charge that passes between 2 points in an electric circuitPotential difference across an electrical component is the amount of energy that is transferred by that electric component per unit of charge

Ammeter measures current (in amps) Must be placed in series Can be put anywhere in the series in the mains circuit But never parallel like the voltmetre

Voltmeter measures voltage/potential difference (in volts) across a component Must be placed in parallel around the component under test

Very basic Used for testing components Used for getting V-I graphs The component, variable resistor and ammeter are all in series They can be put in any order in the main circuit As you vary the variable resistor the current flowing through the circuit changes Allowing you to take several different readings of the ammeter and voltmeter You can plot these values on a V-I graph to find the resistance

V-I GraphsShows how current varies as you change potential difference

Different Resistors The current through a resistor is directly proportional to the potential difference Different resistors have different resistances (hence different slopes)

Filament Lamp As the temperature of the filament increases the resistance increases Hence the curve

Diode Current will only flow through a diode in one direction (only in positive quadrant) The diode has high resistance in the opposite direction

Resistance increases with Temperature When electrical charge flows through a resistor Some of the electrical energy gets transferred to heat energy So the resistor gets hot This causes the ions in the conductor to vibrate more When the ions are moving so much it's hard for the charge-carrying electrons to get through the resistor The current can't flow The resistance increases Most resistors have a limit to how much current can flow More current = increased temperature  Increased temperature= increased resistance Increase in resistance = decrease in current (this is why the graph for the filament levels off at high currents)

The steeper the graph the lower the resistanceIf it curves the resistance is changing

Diode Current only flows in 1 direction Made from a semiconductor material like silicon Used to regulate potential difference

Light-Emitting Diode (LED) Emits light when current flows in a forward direction Used more and more for lighting Use less current They indicate current Often used in TVs, traffic lights etc...

Light Dependant Resistor (LDR) A resistor dependant on the intensity of light bright light = falling resistance darkness= high resistance e.g. automatic outdoor lights

Thermistor Resistance decreases as temperature increases Temperature dependant Hot=resistance drops Cool=increased resistance Make useful temperature detectors e.g. electronic thermoststats

Series Circuit Different components are connected in a line Between + and - power supply (Except voltmeters that are always connected in a parallel) If one thing is disconnected the circuit is broken Has to be complete Not really used for much Potential difference is shared  V1+V2=V Current is the same everywhere A1=A2 The size of current is determined by the total PD Resistance adds up R=R1+R2+R3 The bigger the resistance of a component the bigger the share of total PD Cell voltages add up

Parallel Circuit Each component is separately connected to the + and - power supply If you remove or disconnect one It won't really affect the rest of the circuit Most things are connected this way PD is the same across all components V=V1=V2 Identical bulbs in parallel have the same brightness Current is shared A=A1+A2 Current splits equally at junctions

Ammeters are always connected in seriesVoltmeters are always connected in parallel

Everything in a car is connected din Parallel Means that: Everything can be turned on/off separately Everything gets full voltage of the battery Though it means that the current is divided and lights are dimmer (slightly)

Mains Supply In the UK it's about 230 volts It's AC, alternating current Current is constantly changing direction Frequency = 50Hz Cells and Batteries supply DC, direct current The current always flows in one direction

Oscilloscope Screen Cathode ray oscilloscope (CRO) fancy voltmeter If you plug in an AC supply to an Oscilloscope you get a trace Shows how the voltage of supply changes with time Trace goes up and down in a regular pattern Some positive, some negative The vertical height of the AC show the input voltage By measuring the height you can find the PD of the AC supply DC supply will give you a straight line Voltage is distance between centre line and trace

Reading an Oscilloscope period of an AC supply is the time taken for one complete oscillation. Time between 2 peaks  Frequency of an AC supply is the number of oscillations per second Frequency = 1 ÷ period Remember to convert to seconds if needed UK mains frequency is 50 Hz but you may get other frequencies 

Hazards Long cables Frayed cables Cables in contact with water Water near sockets Damaged plus etc...

Cables have 3 wiresEach has a copper core (good conductor)And a plastic coating (good insulator)

Safety of Wiring Right colour connected in each pin Firmly screwed Cable strip tightly fastened over cable outer layer Different appliances need different amounts of electrical energy Thicker wire = less resistance = greater current

Plug features Metal parts made of copper and brass They're good conductors Casing and outer wires are made of plastic Good conductors

Earthing and FusesPrevent electrical overloads

Static Electricity, Current and voltage

Circuits

Circuit Devices, Parallel and Series

AC and DC, and home electricity

Fuses and Earthing