Where does electricity come from?

1. Where does electricity come from?

2. A short “history” of the universe • Around 14 Billion years ago there was nothing • No time – No space (really, nothing!) • Just an enormous concentration of energy and heat – an infinitely hot and dense fireball existing for ten trillion, trillion, trillionths of a second (10-36) • A fraction of a picosecond (10-12 ) later came the “Big Bang” (or “Big Whoosh” – no sound in space) • The “singularity” became a “plurality” (in science geek terms!) producing all the building blocks for “natures tricks” • At this point the universe began to cool into a melting pot of radiation, matter and anti-matter • The matter and anti-matter went to “war” and matter was the victour • The “survivors” represent around one-half of one percent of the original “combatants”!

3. The “birth” of the atom • The original Big Bang “super force” changed into 4 distinct forces: • Gravity • Strong Nuclear Binding force • Weak Nuclear force • Electromagnetic force • These forces began to construct the material universe • Lots of “exotic” particles formed and were subject to the cosmic version of natural selection • The two lightest particles survived – quarks and Leptons

4. Quarks and Leptons • Within 3 min. after the Big Bang protons and Neutrons appear. • Made up from Quarks • Quarks come in 6 different varieties. • Quarks can only survive in threesomes held together with “gluons” • “up-down-up” = Proton (positive charge) • “down-up-down” = Neutron (no charge) • Neutrons allow Proton to come together to form the nucleus of an atom.

5. Enter The Atom • A few minutes after the Big Bang the universe had cooled to around 1 billion degrees allowing atom nuclei to form. • When the universe cooled to around 3000 degrees a dense fog of electrons (negative charge) could be “captured” by the atom nucleus • Electrons formed by Leptons • In a stable atom the number of electrons equals the number of protons. • Atoms with an excess of electrons are “negative Ions” • Atoms with a deficiency of electrons are “positive Ions”

6. Static vs Current electricity • The ancient Greeks observed that amber rubbed on a cloth attracts light particles • The electrons are removed from the cloth and added to the amber. • Creates Ions • This imbalance creates electric pressure which tries to restore the balance • The difference in charge is called “potential difference” • The discharge of this pressure is called “static electricity” • Two materials with an imbalance of electrons have a potential difference • When these materials are connected together by a conductor (metal) this allows the excess electrons equalise • When the two materials are at equal potential current flow ceases. • Usually obtained from “non-static” sources • These sources can either be: • Direct Current (D.C.) • Alternating Current (A.C.) Static Current

7. Sources of Current Electricity

8. Multiples and Sub-multiples • Used to abbreviate large and small values of a “Standard Unit” • Can be easily converted to/from ENGINEERING NOTATION • Scientific notation is a less structured version of engineering notation.

9. 0.000000000001 • 0.000000001 • 0.000001 • 0.001 • 1000 • 1000000 • 1000000000 • 1000000000000 • 1 x 10-12 • 1 x 10-9 • 1 x 10-6 • 1 x 10-3 • 1 x 103 • 1 x 106 • 1 x 109 • 1 x 1012 • Pico (p) • Nano (n) • Micro (µ) • Milli (m) • Kilo (k) • Mega (M) • Giga (G) • Tera (T) Actual Number Engineering Notation Unit prefix

10. Multiples and Sub-multiples • For both scientific and engineering notation the power or indices represents how many decimal places the decimal shifts; • To the right for a positive number 3.67 x 1011 = 367000000000 • To the left for a negative number 3.67 x 10-11 = 0.0000000000367

11. The Volt • Named after Italian Allesandro Volta (1745 – 1851) • Discovered how to produce and Elecro-motive Force (EMF) from and electrical cell. • EMF – electrical pressure • Equation symbol – V • Unit – Volt (V)

12. The Ampere (Amp) • Named after Frenchman André Marie Ampère (1775 – 1851) • Mathematician and physicist, considered the father of electrodynamics. • Current – flow of electrons in a conductor • Equation symbol – I • Unit – Ampere or Amp (A)

13. The Ohm • Named after German Georg Ohm (1789 – 1854) • Determined that there is a direct proportionality between the potential difference (voltage) applied across a conductor and the resultant electric current – now known as Ohm's law. • Resistance – the opposition of current flow • Equation symbol – R • Unit – Ohm (Ω)

14. Results from experiments • If the Resistance stays constant and the Electromotive force (voltage) is increased: • What happens to the current?

15. Results from experiments • If the Resistance stays constant and the Electromotive force (voltage) is increased: • What happens to the current? • Current increases

16. Results from experiments • If the Resistance stays constant and the Electromotive force (voltage) is increased: • What happens to the current? • Current increases I V

17. Results from experiments • If the Resistance stays constant and the Electromotive force (voltage) is increased: • What happens to the current? • Current increases I α V

18. Results from experiments • If the Resistance in the circuit is decreased and the Voltage stays constant: • What happens to the current?

19. Results from experiments • If the Resistance in the circuit is decreased and the Voltage stays constant: • What happens to the current? • Current increases

20. Results from experiments • If the Resistance in the circuit is decreased and the Voltage stays constant: • What happens to the current? • Current increases I R

21. Results from experiments • If the Resistance in the circuit is decreased and the Voltage stays constant: • What happens to the current? • Current increases I α 1/R

22. Ohm’s Law Ohm’s Law states: states that the current through a conductor between two points is directly proportional to the potential difference or voltage across the two points, and inversely proportional to the resistance between them. V = IR

23. Graph for a 10 Volt Supply

24. Graph for a 1Ω Resistor

25. NOW….. The Maths!!!

26. Quantity of Charge • Q = I x t • Where • Q = charge in Coulombs • I = current in Amperes • t = time in Seconds • 1 Coulomb = 6.242 x 1018 electrons Q I t

27. Mechanical Units(A brief introduction into SI units)

28. Mechanical Units(A brief introduction into SI units)

29. Length vs Distance vs Displacement • Length : how long an object is • Distance : the total length of motion. (in all directions) • Displacement : the total length of motion. (in a straight line “as the crow flies”) Thickness (d) : how wide an object is. Radius (r) : the distance from the centre of a circle to the edge Diameter (d) : the distance from one side of a circle to another.

30. Time, Mass, Current, and Temperature • Time – always expressed in seconds when expressed in a formula. • Mass – originally based on the weight of 1000 millilitres of water at 0º C now the mass of a platinum weight in the Louvre (Paris). (1kg) • Current – One ampere flows when one volt of potential difference is applied to a resistance one ohm or when one coulomb (6.25 x 1018 electrons) flows in a conductor for one second • Temperature – The Kelvin scale starts at absolute 0 (when all molecular movement ceases – minus 273ºC)

31. Force • Generally • Force = Mass x Acceleration • F = ma • In free fall • Force = Mass x Gravity • F = mg • g = 9.8 m/s2

32. Energy and Work • Energy is defined as the ability to do work • Energy (work) = Force x Distance • W = F x l • 2 types – potential and kinetic

33. Power • Power is the ability to do work • Power = work / time • P = W / t Electrical power is the work done by one volt potential and one ampere Power = Voltage x Current P = V x I

34. Power (cont.) • Since P = V x I and V = I x R we can say: • P = (I x R) x I or • P = I2 x R • AND since P = V x I and I = V/R we can say: • P = V x (V/R) or • P = V2 / R

35. Power Dissipationand Power Rating • When current passes through a resistor the work done by the resistor is heat. • This heat is generally unwanted. • This heat is generally express as I2R • All electrical equipment has a power rating equal to the maximum power dissipation. • If the actual power dissipated is greater than this rating then the component will be “cooked”!

36. Power Measurement • Power can be measured by the product of values obtained from a voltmeter and ammeter. • Alternatively power can also be measured using a WATTMETER

37. Examples of the Effects of electic current

38. The 4 main effects of electrical current • I2R or Heat – when electricity flows through a conductor, work must be done to overcome the resistance. Work = Energy = Heat • Magnetic – A conductor carrying current will always have a magnetic field circulating around it. Work = motion • Chemical – the passage of electrons and ions can change the physical and/or molecular structure of matter. • Physiological – electric shock

39. Electrical Heating • Can be useful when heat is a desired effect. (Room heating, melting materials, etc.) • Can be detrimental when heat is an undesired effect. (heating of cables, heat pollution) The principal requirement of electrical conductors and cables is that they carry the required current without becoming too hot for safety.

40. Magnetic Effects of Current • In week one we learnt : The original Big Bang “super force” changed into 4 distinct forces: • Gravity • Strong Nuclear Binding force • Weak Nuclear force • Electromagnetic force • The electromagnetic effect of current is interdependent with current flow • This effect is used in most electrical machines

41. Chemical effects of electric current • Two different effects: • Electrolysis • Voltaic cells • Electrolysis is used in metal refining, battery charging and electroplating. It is also the cause of “galvanic action” (corrosion or rust)

42. Chemical effects of electric current cont. • The Voltaic cell: • Two main types – primary and secondary • A primary cell is made up of two different metals immersed in an acidic or alkaline electrolyte (usually liquid) • A battery is made up of these electrical cells. • Anode – positive electrode • Cathode – negative electrode

43. Physiological effects of an electric current. • The effects on the human body are related to: • The amount of current • The current path • The duration of current flow • The type of circuit with which the contact is made • The voltage of the circuit • The resistance of the human body. • The Electrical Safety act makes compliance with the electrical standard (AS/NZS-3000:2007) mandatory.

44. AS/NZS 3000:2007 – Wiring Rules • “Electrician’s Bible” • 1.1 SCOPE This Standard sets out requirements for the design, construction and verification of electrical installations, including the selection and installation of electrical equipment forming part of such electrical installations. These requirements are intended to protect persons, livestock, and property from electric shock, fire and physical injury hazards that may arise from an electrical installation that is used with reasonable care and with due regard to the intended purpose of the electrical installation. In addition, guidance is provided so that the electrical installation will function correctly for the purpose intended

45. AS/NZS 3000:2007 – Wiring Rules • 1.5 FUNDAMENTAL PRINCIPLES • 1.5.1 Protection against dangers and damage The requirements of this Standard are intended to ensure the safety of persons, livestock, and property against dangers and damage that may arise in the reasonable use of electrical installations.

46. AS/NZS 3000:2007 – Wiring Rules • 1.5.1 Protection against dangers and damage cont. In electrical installations, the three major types of risk are as follows: (a) Shock current Shock current arising from contact with parts that are live in normal service (direct contact) and contact with parts that become live under fault conditions (indirect contact). (b) Excessive temperatures Excessive temperatures likely to cause burns, fires and other injurious effects. Persons, fixed equipment, and fixed materials adjacent to electrical equipment shall be protected against harmful effects of heat developed by electrical equipment, or thermal radiation, particularly the following effects: (i) combustion or degradation of materials; (ii) risk of burns; (iii) impairment of the safe function of installed equipment. (c) Explosive atmospheres Equipment installed in areas where explosive gases or dusts may be present shall provide protection against the ignition of such gases or dusts.

47. AS/NZS 3000:2007 – Wiring Rules • Direct contact – Basic protection – contact with live parts under “normal” conditions

48. AS/NZS 3000:2007 – Wiring Rules 1.5.3 Protection against electric shock 1.5.3.1 Scope Protection shall be provided against shock current arising from contact with parts that are live in normal service (direct contact) or parts that become live under fault conditions (indirect contact). Therefore, live parts must not be accessible and accessible conductive parts must not be live, neither under normal conditions nor under single fault conditions.

49. AS/NZS 3000:2007 – Wiring Rules 1.5.4 Basic protection (protection against direct contact) 1.5.4.1 General Protection shall be provided against dangers that may arise from contact with parts of the electrical installation that are live in normal service. 1.5.4.2 Methods of protection Basic protection shall be provided by one or any combination of the following methods: (a) Insulation, in accordance with Clause 1.5.4.3. (b) Barriers or enclosures, in accordance with Clause 1.5.4.4. (c) Obstacles, in accordance with Clause 1.5.4.5. (d) Placing out of reach, in accordance with Clause 1.5.4.6. RCDs are not recognized as a sole means of basic protection against contact with live parts but may be used to augment one of the above methods.

50. AS/NZS 3000:2007 – Wiring Rules • Indirect contact – fault protection – contact with live parts under “fault” conditions