Household Electricity

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Household Electricity

  1. 1. E5: Household Electricity Textbook Page 76
  2. 2. Objectives <ul><li>At the end of this lesson, you will be able to: </li></ul><ul><ul><li>Understand what is power stations and energy sources </li></ul></ul><ul><ul><li>State its electrical power and its units </li></ul></ul><ul><ul><li>Differentiate between power of electrical appliances and power from power stations </li></ul></ul>
  3. 3. Look at the picture… <ul><li>What is this? </li></ul><ul><li>Where is it located? </li></ul><ul><li>What it does? </li></ul>
  4. 4. How does Singapore get its electricity? <ul><li>Power stations </li></ul><ul><li>Generate electricity from oil and natural gas </li></ul><ul><li>Transmit to homes and industries all over the country </li></ul>
  5. 5. What is POWER? <ul><li>120 V </li></ul><ul><li>7 W </li></ul><ul><li>W = watts </li></ul>
  6. 6. What is POWER? <ul><li>The larger the watts the brighter the bulb </li></ul><ul><li>100 W is brighter than 60 W bulb. </li></ul><ul><li>100 W has more power </li></ul><ul><li>The power of an electrical appliance is the amount of electrical energy it converts to other forms of energy in one second </li></ul>
  7. 7. POWER <ul><li>Power is measured in watts (W) </li></ul><ul><li>Larger unit = kilowatt (kW) </li></ul><ul><li>1 kW = 1000 W </li></ul>
  8. 8. Power of electrical appliances <ul><li>Different electrical appliances have different power ratings </li></ul><ul><li>Do Inquiry time - pg79 </li></ul>
  9. 9. Power from power stations <ul><li>Power stations need to generate a lot of power </li></ul><ul><li>Measured in megawatts (MW) </li></ul>
  10. 10. How do power companies know how much electricity we consume? <ul><li>Electricity meters </li></ul><ul><li>Unit for electricity meters = kilowatt-hour (kWh) </li></ul><ul><li>Energy consumed (in kWh) = Power (in kW) X Time (in hours) </li></ul><ul><li>Cost of electrical energy = units of electrical energy used (kWh) x Cost per unit </li></ul>
  11. 11. Calculation Exercises <ul><li>An electric kettle has a power rating of 2400 W. It has been used to keep water warm for 2 hrs. Calculate the cost of the electricity used if each unit costs is 17 cents. </li></ul>
  12. 12. Calculation Exercises - Answer <ul><li>Power of appliance = 2400 W = 2.4 kW </li></ul><ul><li>Time in use = 2 h </li></ul><ul><li>Energy consumed = 2.4 x 2 = 4.8 kWh </li></ul><ul><li>Cost of electricity = 4.8 x 0.17 = $0.82 </li></ul>
  13. 13. Calculation Exercises <ul><li>A fan has a power rating of 3600 W. It has been used to keep room cool for 720 mins. Calculate the cost of the electricity used if each unit costs is 20 cents. </li></ul>
  14. 14. Calculation Exercises - Answers <ul><li>Power of appliance = 3600 W = 3.6 kW </li></ul><ul><li>Time in use = 720 mins = 12 h </li></ul><ul><li>Energy consumed = 3.6 x 12 = 43.2 kWh </li></ul><ul><li>Cost of electricity = 43.2 x 0.20 = $8.64 </li></ul>
  15. 15. Do inquiry time and checkpoint Textbook Page 81
  16. 16. Objectives <ul><li>At the end of this lesson, you will be able to: </li></ul><ul><ul><li>State examples when electricity can be dangerous </li></ul></ul><ul><ul><li>State the safety features in circuits and appliances </li></ul></ul><ul><ul><li>State the safety precautions when using electricity </li></ul></ul>
  17. 17. Electricity can be dangerous <ul><li>Main dangers: </li></ul><ul><ul><li>Electric shock </li></ul></ul><ul><ul><li>Electrical fire </li></ul></ul>
  18. 18. Electricity can be dangerous <ul><li>Frayed and damaged wires </li></ul><ul><li>If the person touches a bare wire, current flows through the body </li></ul><ul><li>Electric shock </li></ul>
  19. 19. Electricity can be dangerous <ul><li>Overloading </li></ul><ul><li>Adapters are used to connect more than one appliance to a main socket </li></ul><ul><li>Large current causes the wire to get hot </li></ul><ul><li>When the current is too large, the circuit is said to be overloaded </li></ul>
  20. 20. Electricity can be dangerous <ul><li>Short circuits </li></ul><ul><li>Broken or bare wire in a circuit may touch another wire in the circuit causes a short circuit </li></ul><ul><li>Cause fire in the wires or in the appliance </li></ul>
  21. 21. Electricity can be dangerous <ul><li>Wet Conditions </li></ul><ul><li>If a person touches a damaged electrical wire or appliance with wet hands, an electric current may flow through his body – electric shock </li></ul>
  22. 22. Safety features in circuits and appliances <ul><li>Fuses </li></ul><ul><ul><li>It is placed in the circuit </li></ul></ul><ul><ul><li>It is a short length wire that melts and breaks when the current in the circuit is too large </li></ul></ul><ul><ul><li>Thus causes circuit to open </li></ul></ul><ul><ul><li>And no current flow </li></ul></ul><ul><ul><li>Found in electrical appliances, </li></ul></ul><ul><ul><li>electric plugs and fuse boxes </li></ul></ul>
  23. 23. Safety features in circuits and appliances <ul><li>Circuit Breakers </li></ul><ul><ul><li>Many buildings use circuit breakers </li></ul></ul><ul><ul><li>Special switch </li></ul></ul><ul><ul><li>If current in a circuit becomes too large, the switch will turn off by itself </li></ul></ul>
  24. 24. Safety features in circuits and appliances <ul><li>Main Switch </li></ul><ul><ul><li>Switches on and off the main electric supply to the whole building </li></ul></ul><ul><ul><li>If there is a fire, switch off the main switch </li></ul></ul>
  25. 25. Safety features in circuits and appliances <ul><li>Earth Wire </li></ul><ul><ul><li>Electricity flows through the live wire but not the earth wire </li></ul></ul><ul><ul><li>Earth wire is for safety </li></ul></ul><ul><ul><li>Earth wire connected to metal casing, most current flows to the ground through the earth wire instead </li></ul></ul><ul><ul><li>So you will not get electric shock </li></ul></ul>
  26. 26. Safety precautions when using electricity <ul><li>Never touch bare or broken wires </li></ul><ul><li>Never touch appliances/switches with wet hands </li></ul><ul><li>Never overload a circuit </li></ul><ul><li>Never use electric appliances in wet places </li></ul><ul><li>Do not push anything into sockets </li></ul><ul><li>Never put nails into walls near switches, sockets and wires </li></ul><ul><li>Do not use electrical appliances with old or frayed wires </li></ul>
  27. 27. Objectives <ul><li>At the end of this lesson, you will be able to: </li></ul><ul><ul><li>State how we can save electricity </li></ul></ul>
  28. 28. What can we do to save electricity? <ul><li>Switch off lights, electrical appliances when not in used </li></ul><ul><li>Use energy efficient lamps </li></ul><ul><li>Set thermostat of air conditioner at a higher temperature </li></ul>
  29. 29. Do checkpoint Page 87

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