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Electricity ► Idea map 1 Atom Electron Proton Neutron Moving Stationary Current Charge Voltage Energy Mains Control Cost
Electricity ► Voltage ► Idea map 1.1 Energy Electrons causes... Voltage Current Circuit Series Parallel Components Ammeter Voltmeter Thermistor LDR
Electricity ► Voltage ► Energy and Electrons • Electricity is fundamentally about 2 things… • Energy • Ability to do • Invisible • Electrons • Tiny particle • Carry charge • Carry Energy • Effectively Invisible
Electricity ► Voltage ► Current • Electric Current • Current • Flow of charge • Electricity • Moving Electrons • Symbol I Mean the same Small Current Large Current
Electricity ► Voltage ► Amps A • The current flowing through a component in a circuit is measured in amperes (A). • An ammeter is connected in series with the component. • 1 Amp = 6 billion billion electrons per second
Electricity ► Voltage ► Voltage Idea • Energy per electron • Voltage • Potential Energy • Potential • Symbol V Mean the same High Voltage Low Voltage Low energy Electron High energy Electron
Mean the same Energy Electricity ► Voltage ► Potential Difference • Potential Energy Difference between 2 points on a wire • Potential Difference • P.D. • Difference in Voltage • Voltage across
Electricity ► Voltage ► Voltmeter V • 4 Volts • The p.d. across a component in a circuit is measured in volts (V) • A voltmeter connected across (in parallel with) the component.
The next four slides make essentially the same point about the relationship between current and voltage… Relationship Proportional Connection One can be worked out from the other One causes a change in the other Link A formula allows us to calculate a value Dependent Electricity ► Voltage ► Relationship Concept Mean the same
A current will flow through an electrical component (or device)… Only if there is a voltage or potential difference (p.d.) across its ends. Electricity ► Voltage ► Voltage needed
The bigger the potential difference across a component… The bigger the current that flows through it. Electricity ► Voltage ► More voltage, more current
Proportional : As one value increases so does a second value Electricity ► Voltage ► Graphing Relationship Current Voltage • Current-voltage graphs are used to show how the… • Current through a component varies with the voltage across it.
Electricity ► Voltage ► V = I R • The current through a resistor (at constant temperature) is proportional to the voltage across the resistor.
3 A 12 V 3 A 3 A 6 V 6 V 2 Ω 2 Ω 4 Ω Electricity ► Voltage ► Series Circuit • When components are connected in series: • Their total resistance is the sum of their separate resistances. • The same current flows through each component. • The total potential difference of the supply is shared between them
12 V 3 A 3 A 12 V 2 A 12 V 1 A Electricity ► Voltage ► Parallel Circuit • When components are connected in parallel: • The current in the branches equals that leaving the battery • The current may vary from branch to branch • The total potential difference of the supply is same for each branch
Electricity ► Voltage ► Filament Bulb Resistance Temperature • The resistance of a filament lamp increases… • As the temperature of the filament increases.
Electricity ► Voltage ► Diode CURRENT normal flow VOLTAGE no flow • The current through a diode flows in one direction only. • The diode has a very high resistance in the reverse direction.
Electricity ► Voltage ► Light Dependent Resistor 1000 Ω 10 Ω • Could be called “darkness dependent resistor” • The resistance of a light dependent resistor decreases… • As the light intensity increases. • It resists when it is dark…
Electricity ► Voltage ► Thermistor 1000 Ω 10 Ω • A “coldness dependent resistor” • The resistance of a thermistor decreases… • As the temperature increases. • Resists when it is cold
V A Electricity ► Voltage ► Symbols • Cell • Switch (open) • Battery • Switch (closed) • Variable resistor • L.D.R • Diode • Fuse • Resistor • Ammeter • Lamp • Thermistor • Voltmeter
Electricity ► Energy ► Ideas map 1.2 Electrons Coulomb deliver… in a certain… Energy (J) Time (s) to give us… Power Watt (J per s) Voltage Current x
Electricity ► Energy ► Electrons carries energy 10 J £20 • This is an electron • It collects energy at the battery… • Travels around a circuit… • And delivers it to a component
Electricity ► Energy ► Electrons deliver Energy £30 30 J Bank Shop Shop £20 20 J 10 J £10 • As an electric current flows through a circuit, energy is transferred • The energy is transferred from the battery or power supply… • …to the components in the electrical circuit.
Electricity ► Energy ► Heat from a wire • When Charge flows through a resistor, electrical energy is transferred as heat.
Electricity ► Energy ► Energy per Time £10 £10 10 J 10 J
Electricity ► Energy ► Power 10 J 10 J • Power is energy transferred per second • Power is measured in Joules per Second known as a Watt • 1 Watt = 1 J of energy in 1s
1km 1km 1km 1km 1km 1km 2 cubic kilometres contain about 6 billion billion grains of salt Electricity ► Energy ► Coulomb • Seconds are inconveniently small to measure the age of a person. • We use a word which means 31,536,000 seconds. • The word is year. • Electrons are inconveniently small to measure everyday numbers of electrons. • We use a word which means 6,000,000,000,000,000,000 electrons • The word is Coulomb.
Electricity ► Energy ► E = VQ 50 J 50 J • The higher the voltage of a supply… • the greater the amount of energy transferred for… • a given amount of charge which flows.
3 Coulombs / Sec (3 Amps) Equals 15 Coulombs Electricity ► Energy ► Q = I t …For 5 Seconds…
Electricity ► Energy ► Table of 7 key ideas DESCRIPTION NAME SYMBOL UNIT Ability to do Energy E Joule (J) Electrons Charge Q Coulomb (C) Change Time t Second (s) Charge per Time Current I Amp (A) Energy per Charge Voltage V Volt (V) Energy per Time Power P Watt (W) Obstacle Resistance R Ohm (Ώ)
R V I E Q t P Electricity ► Energy ► 7 ideas connected • 1 . V = I R • E = V Q • E = P t • Q = I T • P = I V
Electricity ► Mains ► Ideas map 1.3 Types of Current Direct Alternating Mains Plug Safety Live Neutral Earth Fuse Circuit Breaker
Electricity ► Mains ► Mains voltage • The UK mains supply is about 230 volts. • Mains can kill if it is not used safely.
Electricity ► Mains ► Plug • Earth pin • Copper Core • Plastic Layer • Fuse • Live pin • Plastic Case • Neutral Pin • Cable grip • Brass Pins and Copper Wires are conductors, plastic is an insulator
Electricity ► Mains ► Alternating Current • An alternating current (a.c.) is one which is constantly changing direction. • Mains is an a.c. supply. • In the UK it has a frequency of 50 cycles per second or 50 hertz (Hz) which means that it changes direction and back again 50 times each second.
Electricity ► Mains ► Direct Current • Cells and batteries supply a current which always flows in the same direction. • This is called a direct current (d.c.).
Electricity ► Mains ► Oscilloscope Trace a.c. d.c. • Candidates should be able to compare the voltages of d.c. supplies… • And the frequencies and peak voltages of a.c. supplies from diagrams of oscilloscope traces.
Electricity ► Mains ► Safety • If a fault in an electrical circuit or an appliance causes too great a current to flow, the circuit is switched off by a • fuse • or a circuit breaker.
Electricity ► Mains ► Fuse Normal Fault 14 A 12 A Fuse : 13 A Fuse : 13 A • When the current through a fuse wire exceeds the current rating of the fuse.. • The wire becomes hot and will (eventually) melt breaking the circuit and switching off the current.
Electricity ► Mains ► Fuse selection 13 • The Goldilocks and the Three • Bears Theory of Fuse Selection™ • Melts too late 10 5 • Just right 3 • Melts too soon 2 • Dangerous • Safe • The fuse should have a value higher than, but as close as possible to, the current through the appliance when it is working normally. • The manufacturer will normally recommend a fuse.
Electricity ► Mains ► Circuit Breaker Normal Fault Strong Magnetic Force Weak Magnetic Force High Current Safe Current • A circuit breaker uses an electromagnet to detect a surge and operate a very quick automatic off switch. • When the fault is fixed the circuit breaker can be reset.
Electricity ► Mains ► Earth Wire Earth Wire No Earth Wire Exposed Wire • Appliances with metal cases need to be earthed. • The earth pin is connected to the case via the yellow/green wire. • If a fault in the appliance connects the case to the live wire, and the supply is switched on, a very large current flows to earth and overloads the fuse.
Electricity ► Mains ► Live Wire • The live terminal of the mains supply alternates between a positive and negative voltage with respect to the neutral terminal. • The neutral terminal stays at a voltage close to zero with respect to earth.
Electricity ► Charge ► Idea Map 1.5 Electrons & Protons Extra Electrons Equal Lack of Electrons Negative Neutral Positive Force Force Attraction Uses Photocopier Electrolysis Printer
+ + + + + + + + + - - - - - - - - - Electricity ► Charge ► Balance of Protons and Electrons Electrons Protons Extra Electrons Equal Lack of Electrons Negative Neutral Positive
Electricity ► Charge ► Multiple Terms • Charge • Property of Electrons and Protons • Particles which can exert a force • Ability to create movement Mean the same • Stationary Electrons • Electrostatics • Static Electricity • Static • Trillions of Electrons ‘flooding in’ • Trillions of Electrons leaving an area • The balance between Electrons and Protons Mean the same • Negatively Charged: Extra Electrons • Positively Charged: Electrons missing Both Electrically Charged
Electricity ► Charge ► Phenomena • When certain different insulating materials are rubbed against each other they become electrically charged. • Electrically charged objects attract small objects placed near to them.
+ + + + + + + + - - - - - - - - - - - - - Electricity ► Charge ► Charges cause Repulsion and Attraction • When two electrically charged objects are brought close together, they exert a force on each other. • These observations can be explained in terms of two types of charge called positive (+) and negative (-). • Two objects which have the same type of charge repel. • Two objects which have different types of charge attract.