Electricity:

1. Electricity:

2. Using electricity • In 1771, Luigi Galvani discovered that the muscles of dead frogs twitched when struck by a spark • May have inspired the idea behind the story Frankenstein

3. How do we get Electricity?

4. How to generate electricity Generation of Electricity = [Coil of Wire] +  [Magnetism] +  [Relative Motion]

5. How does an electric system work? • The basic components are: • Power Plant: Electricity is produced here • Power Grid: A network that connects power plants to substations and substation to homes. • Transmission Substation: Transformers increase voltage so that volts can be sent over long distances. • Distribution Substation: Transformers reduce voltage to a level suitable for the surrounding community • Distribution System: Delivers electricity to homes and businesses. Line may be a underground or overhead. • Service Connection: Connection of customers to the grid. A meter is connected also to measure the amount of electricity used by customers

6. Electrical Flow • When you switch something on, you complete a pathway for electricity to flow through. • The pathway that allows electrical energy to flow is called an electric circuit. • Electric circuits consist of three components: • A Power Supply: Provides electrical energy • A Load: Converts electrical energy into another form • A Conducting Path: Allows electric charge to flow around the circuit.

7. Electric Circuits • Electric circuits consist of three components: • A Power Supply: Provides electrical energy • A Load: Converts electrical energy into another form • A Conducting Path: Allows electric charge to flow around the circuit.

8. A simple electric circuit Power Supply Load Conducting Path

9. Circuit Diagram symbols = = =

10. Current • Current measures the amount of charge flowing through a circuit . • A large current has more charge flowing every second than a small current.

11. Measuring Current • Current is measured in a unit called ampere (A)or ‘amps’ • Milliamps (mA) are used to measure small currents. • Current can be measured using a device called an ammeter. • Ammeter’s need to be inserted into the circuit to get a reading.

12. Measuring Voltage • Voltage is measure in Volts (V) • A device that measures the amount of volts passing through a circuit is called a voltmeter

13. Voltage • Voltage is a measure of the amount of energy there is to push charge through a circuit. • Voltage is supplied by batteries, power packs and power points.

14. Energy Sources

15. Energy Sources • Batteries, power packs or power points are all considered energy sources. • They provide all the electric energy and voltage to a circuit. • Energy sources create an electric field that pushes electrons around a circuit.

16. Power points and power packs • Power points supply approximately 240 volts into your home • Power packs like the ones we use in class supply up to 12 volts • The power for which is produced in a variety of power plants.

17. Batteries • Batteries are used when we need portable energy sources. • 1 AA battery provides 1.5 volts • While car batteries provide 12 volts • Batteries are made up of cells. • These cells can be either wet or dry.

18. Wet Cell • In this wet cell, zinc reacts with the acid and releases electrons. • If a circuit is connected to the plates then the electrons will flow to the copper plate • As they flow through the circuit the globe will light. • Wet cells are usually large and heavy and can leak acid if tipped over.

19. Example – Wet Cell. • A car battery is a collection of wet cells. • The wet substance is sulfuric acid • The plates are made of lead and lead oxide. • While a car is running it reverses the chemical reaction recharging the battery. • Eventually chemicals build up on the plate and the batter “dies”.

20. Dry Cell • Being large and heavy wet cells are useless for small devices like: • Ipods • Laptops • Remotes • They use small portable cells called dry cells. • Dry cells contain a chemical paste and their electrodes are designed to save space. • It is common that several batteries are connected together to supply more voltage. = 4.5 volts

21. Photovoltaic Cell • A photovoltaic cell (or solar )is made up of two layers. • These two layers are semiconductors. • When sunlight strikes the top layer electrons are given energy to move to the bottom layer. • This creates an electric current.

22. electrolocation The Living Battery -Electrophorus Electricus • Aka the electric eel • Actually a freshwater fish. • It can produce up to 600 volts • This is five times the amount found in an electrical outlet • Uses the electric field to stun fish and to see

23. Activity: Virtual solar race challenge • http://wsc.pv.unsw.edu.au/ • This website allows you to build and name a virtual solar powered car • You are then able to race it against computer generated cars.

24. Activity: Virtual solar race challenge • The important feature of this game is the design process. • You have a limited budget of $240,000 to build your car. • You need to decide on what balance of components are important for speed and power.

25. Conductors and Insulators

26. Conductors • A conductor is a substance that allows current to flow through it easily. • Examples are metals like: • Copper: used commonly in electric circuits • Aluminium: More expensive, used when copper is unsuitable.

27. Insulators • Materials that do not allow current to pass through them are called Insulators. • Examples of insulators: • Plastic • Rubber

28. Activity: What is a Superconductor ? Brief research assignment. • What are superconductors ? • What uses are there for superconductors? • Briefly describe how they work. • Useful links: • http://superconductors.org/INdex.htm • http://science.howstuffworks.com/question610.htm

29. Energy Users

30. Not all metals conduct the same • All metals conduct electricity, but some do so better than others. • Tungsten and nichrome for example are not very good at conducting electricity. • Therefore electricity flows easier in copper wires than in tungsten. • This is called resistance.

31. Resistance • Resistance converts electrical energy into heat and light. • This is used in light globes with tungsten filaments. • Conductors have a low resistance • Insulators have a high resistance

32. Short Circuit! • Without any resistance (such as a globe or heating element) too much current can flow through a circuit. • This may generate too much heat in connecting wires or the energy source. • This might damage the circuit causing it to melt or catch fire! • This is known as a Short Circuit

33. Using Circuits

34. Series circuits • If two globes are arranged in a single line then they are said to be in series. • Although the current is said to each globe is the same, the voltage is shared between the two. • This means that the globes will both glow more dimly. • If one of the bulbs is removed or ‘blows’ then the other globes in the circuit will not light up.

35. Parallel circuits • If two globes are arranged in separate branches of a circuit then the are said to be in parallel. • Each globe has the same amount of energy and voltage supplied to them . • The current is divided between them, • This means that they will glow with the same ‘brightness’ • Also if one globe is removed from this circuit the other will still remain lit.

36. Examples – Fairy Lights SERIES Parallel • In a parallel circuit all lights are powered by a low voltage source. A transformer reduces the voltage from 240 volts to 12 volts. All globes receive 12 volts. • Advantages: • If one globes breaks all the other globes still have power. • This makes it easier to find the broken globe. • A series circuit arranged of 20 lights would share 240 volts from a power point. • Therefore each globe receives 12 volts. • Disadvantages: • If one globes broke then all the other globes with also go out • This would make it difficult to find the bad globe.

37. Comparison of Series and Parallel

38. Complex circuits • Circuits can be combinations of series and parallel sections. • Current will always take the easiest way through a circuit. • A section with a single globe will be easier to travel on than a section with two. • Also it will carry twice as much current.

39. Household Circuits • Electrical wiring within you house is one big parallel circuit • Electrical companies supply 240 volts to your house. • Each power point creates an extra parallel section that receives the same 240 volts.

40. AC/DC • Direct Current (DC) • When the current flows in only one direction. • An example of this is a battery. • Alternating Current (AC) • Current flows backwards and forwards. • Energy is supplied to houses like this because it is easier to generate and transmit.

41. Electrical Safety.

42. ? What is wrong with this picture?

43. When something goes wrong • Short circuits occur when an easier path for current is created. • A huge current flows through causing the circuit to overheat and melt. • You could even become part of the circuit and be shocked or electrocuted! • To prevent this home circuits have fuses or circuit breakers. What's wrong here?

44. Fuses • A fuse is a thin metal wire, that breaks when too much current passes through it. • Fuses are rated according to the amount of current that causes them to melt. • Therefore a 5 amp fuse will melt at a current of 5 or more amps.

45. Circuit Breakers • Fuses used to be the most common method for protecting circuits within a house. • These days new houses are built with circuit breakers instead. • Circuit breakers are special switches that ‘trip’ (turn off) the circuit if too much current flows through.

46. Electric Shock • Electric shock and electrocution (death by electricity) will occur if current finds a path through the body. • Only a small current can cause death. • The current damages your tissues and interferes with the electric signals that drive the heart and the brain.

47. Idiots and Electricity Step 1: Climb electrical pole. Step 2: Reach out and touch high voltage conductor. Step 3: 16,000 volt Human fireball!

48. Electrical Burns

49. Emergency Procedures • If you find someone who has collapsed from an electric shock: • Call OOO • Switch off main power (if possible) • Do not touch the person (otherwise you will get shocked) • You may be able to move the person if you use an insulating material (plastic rope, garden hose)

50. The Electric Chair • The electric chair was invented to replace hanging as a method of execution. • It was intended to be a quick and painless alternative • In the first ever electric chair execution 1000 volts were applied. • This burnt skin and burst blood vessels • It still took another 70 seconds at 1300 volts to kill the prisoner. • Other prisoners convulsed so violently they broke their own arms and legs. • So really its not all that quick and painless !