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KS4 Electricity – Mains Electricity

KS4 Electricity – Mains Electricity. Mains Electricity. What is mains electricity?. The electricity we get from plug sockets. NEVER STICK ANYTHING IN A PLUG SOCKET!. Electrical cable. Electrical cable connects the plug to a device. What does the cable look like inside?.

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KS4 Electricity – Mains Electricity

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  1. KS4 Electricity – Mains Electricity

  2. Mains Electricity What is mains electricity? The electricity we get from plug sockets. NEVER STICK ANYTHING IN A PLUG SOCKET!

  3. Electrical cable Electrical cable connects the plug to a device. What does the cable look like inside? How is it designed for maximum safety?

  4. Electrical cable cross- section The cable contains three wires. What material is the wire? Copper Each wire is encased in plastic. Why is plastic used? Plastic is an electrical insulator. The wires are then encased in another insulating layer of plastic.

  5. Three copper wires The three copper wires have different functions. The colour of the plastic casing tells you what the wire is. Earth Green and yellow Neutral Blue Brown Live

  6. The Live wire The Live wire carries a current that alternates between negative and positive values. What is this type of current called? Alternating Current (A.C.) The Live wire is connected to the Live pin. Which is the live pin?

  7. The Neutral wire The Neutral wire stays at a voltage close to zero with respect to Earth. What colour is the Neutral wire? Blue The Neutral wire is connected to the Neutral pin. Which is the neutral pin?

  8. The Earth wire If an appliance has a metal case it needs to be earthed. The Earth wire connects the appliance case to the Earth pin. If there is a fault that connects the live wire to the appliance case a very large current flows to earth and overloads the fuse. What colour is the Earth wire? Green and yellow Which is the Earth pin?

  9. Materials Material Brass Copper Plastic Used for Plug case Pins Wires Useful Property Good conductor Good insulator Good conductor

  10. Electrical surges If there is a surge of electrical current in the mains supply this could damage any appliances or devices connected to the mains supply. What could cause such an electrical surge? A lightning strike! • Name two ways of protecting devices from electrical surges: • _______________ • _______________ Fuses Circuit breakers

  11. AC/DC What is AC? Source of AC? AC is alternating current, a current which is constantly changing in direction. Mains electricity (50Hz) Sources of DC? What is DC? Cells or batteries DC is direct current, current that is always flowing in one direction.

  12. AC/DC signal simulation Use the animation below to recreate different a.c. or d.c. signals.

  13. Fuses I What is a fuse? A fuse is a device that is used to protect devices from a current which is too high. How does a fuse work? As current flows along a conductor there is friction between the electrons and the atoms of the conductor. The more current, the more friction. The friction causes heat, and the more current the hotter the fuse gets. Fuses contain pieces of conductor that melt if the current is too high. When the fuse melts, it breaks the circuit.

  14. Fuses II What is the circuit symbol for a fuse? Fuses are labelled with the maximum current they are designed to allow. When choosing the fuse for a device you should always choose one with the ampage above the operating current of the device. Example: So if a kettle operates with an electrical current of 4.3A what fuse should you use? You can choose from fuses of 3A, 5A, 8A and 13A. use a 5A fuse

  15. Fuses II For the following devices choose fuses from 3A, 5A and 13A. 3.0A 13.0A 5.0A 13.0A 5.0A 13.0A

  16. Power calculations and fuses If you have a lamp and it has a potential difference of 200V across it and it operates at a power of 60W: A) What current is running through the lamp? B) What fuse should be fitted to the plug of the lamp? A) P = IV I = P/V I = 60W / 200V I = 0.3A B) A 3A fuse should be fitted to the plug.

  17. Power calculations and fuses If you have a cooker and it has a potential difference of 230V across it and it operates at a power of 9.2kW: A) What current is running through the cooker? B) Why should a 13A fuse not be fitted to the plug? A) P = IV I = P/V I = 9 200W / 230V I = 40A B) The fuse would blow each time the cooker was turned on.

  18. Can you label the plug? Live terminal Neutral terminal Earth terminal Cable grip Fuse

  19. The Circuit breaker switch electromagnet What happens if the current is too large? Too much current causes the electromagnet to produce a magnetic field strong enough to open the switch. (The circuit break is said to ‘trip’). This switches off the current.

  20. lights Domestic wiring system 5A 30A Ring Main Power Points kWh Meter earth live neutral

  21. Buying electricity In your home will be an electricity meter. It records how much electricity you use in units. From the number of units you use your electricity bill is calculated. 26 How many units have been used here? ______ 06895674 06895702

  22. Cost of electricity The cost of electricity is the number of units multiplied by the cost per unit: Cost = Number of units x cost per unit Example: How much would 10 units of electricity cost at a price of 9p per unit? Cost = 10 x 9p = 90 p

  23. What is one unit of electricity? Energy = Power x time Units: kWh 1 unit of electricity = 1 kWh Example: How many units of electricity is 17.6 kWh? 17.6 units

  24. Buying electricity – question 1: A kettle uses 45.2 kWhr of energy. If electricity costs 10p per unit, how much does it cost to use the kettle? Number of units: Number of units of electricity is 45.2 units Cost of electricity: Cost = 45.2 x 10 p = 452p or £4.52

  25. Buying electricity - question 2: An iron that operates at a power of 3 KW for 4 hours uses electricity that costs 8p per unit. How much does it cost for the electricity that it uses? Number of units: kWhr = 3kW x 4hr = 12 kWhr Number of units of electricity is 12 units Cost of electricity: Cost = 12 x 8 p = 96p

  26. Green Yellow Green and Yellow Brown What colour is the live wire? 

  27. It is an electrical insulator It is flexible It is an electrical conductor It is cheap Why are the wires in an electrical cable made from copper? 

  28. 3A 5A 1A 13A If a kettle operates at an electrical current of 6.7A, what fuse should be fitted to the kettle? 

  29. 3A 5A 8A 13A If an electric fan operates at an electrical current of 3.5A, what fuse should be fitted to the fan? 

  30. Brass pins Copper wires Cable-grip Made in U.K. Which of the following is a safety feature of a 3-pin plug? 

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