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Phyin c19 practical electricity

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  • http://en.wikipedia.org/wiki/Battery_(electricity)
  • Transcript

    • 1.
      • Describe the heating effect of electricity in appliances such as electric kettles, ovens and heaters
      • Recall and apply P = V I and E = V I t to new situations or to solve related problems
      • Calculate cost of using electrical appliances where the energy unit is kWh
      • State hazards of using electricity
      • (i) damaged insulation
      • (ii) overheating of cables
      • (iii) damp conditions
      Learning outcomes
    • 2.
      • Explain the use of fuses and circuit breakers in electrical circuits and of fuse ratings
      • Explain the need for earthing metal cases and for double insulation
      • State meaning of ‘lives’, ‘neutral’, ‘earth’
      • Describe the wiring in a mains plug
      • Explain why switches, fuses and circuit breakers are wired into the live conductors
      Learning outcomes
    • 3. 19.1 Electric Power and Energy
      • Heating Elements
      • Electrical appliances use heating effect of electrical current
      • Appliances have heating element – usually made of nichrome wire coiled round an insulating fire-proof materials
      • Nichrome has high resistivity, high melting point, does not oxidise easily at high temperature
    • 4. 19.1 Electric Power and Energy
    • 5. 19.1 Electric Power and Energy
      • Calculation of Electrical Energy
      • When current flows through a conductor, energy released is E = V I t = I 2 Rt = V 2 t÷R
      • Calculation of Electrical Power
      • Electric power is the energy released per unit time
      • P = V I = I 2 R = V 2 ÷R
      • SI unit is watt ( W )
    • 6. 19.1 Electric Power and Energy
    • 7. 19.1 Electric Power and Energy
    • 8. 19.1 Electric Power and Energy
      • Measuring Electricity Consumption
      • Kilowatt (kWh): unit of electrical energy
      • 1 kWh is energy used by a 1 kW electrical appliance in 1 hour
      • Energy released = power × time
      • 1 kWh = 1 kW × 1 hour
      • = 1000 W × 3600 s
      • = 3600 000 J
      • = 3.6 MJ
      • Why is kilowatt-hour used
      • instead of joule to measure
      • electrical consumption?
    • 9. 19.1 Electric Power and Energy
    • 10. 19.1 Electric Power and Energy
      • Measuring Electricity Consumption
      • 1.5 kW air-con switched on for 8 hours uses 1.5 kW × 8 h = 12 kWh
      • 5 kW electric oven switched on for 30 minutes uses 5 kW × 0.5 h = 2.5 kWh
      • A 100 W light bulb switched on for 5 hours uses 0.1 kW × 5 h = 0.5 kWh
    • 11. 19.1 Electric Power and Energy
    • 12.
      • When current flows through a conductor, energy released is
      • E = V I t = I 2 Rt = V 2 t ÷ R
      • Electric power is the energy released per unit time
      • P = V I = I 2 R = V 2 ÷ R
      • kWh is the unit of electrical energy used commercially
      • 1 kWh is the energy used by a 1 kW electrical appliance in 1 hour
    • 13.  
    • 14. 19.2 Dangers of Electricity
      • Electric shock, fire
      • 1. Damaged insulation
        • exposed live wire can cause electric shock
        • damaged insulation between live and neutral wire may result in a short circuit leading to fire
      • 2. Overheating of cables
        • thin wire  higher resistance  more heat produced damage wire insulation  cause fire
        • overloaded power outlet  overheating  cause fire
    • 15.
      • 3. Damp conditions
        • Dry skin has resistance of 100 000 ohms or more
        • Wet skin reduces resistance drastically to few hundred ohms
        • Keep switches, plugs, sockets, connecting wires dry
        • Never operate electrical appliance with wet hands
      19.2 Dangers of Electricity
    • 16. 19.2 Dangers of Electricity Physiological effects of an electric current
    • 17. 19.2 Dangers of Electricity
    • 18.
      • Two major dangers when using electricity are electric shock and fire
      • Damaged insulation, overheating of cables and damp conditions are some causes of electrical accidents
    • 19. 19.3 Safe Use of Electricity in the House
      • Mains cable: live wire, neutral wire
      • Mains cable connected to mains fuse , electricity meter and consumer unit
      • Consumer unit has main switch or earth leakage circuit breaker
      • Fuse or miniature circuit breaker (MCB) is used for each power circuit of the house
      Consumer unit with circuit breakers for each circuit in the house
    • 20. 19.3 Safe Use of Electricity in the House Household Electrical Wiring
    • 21. 19.3 Safe Use of Electricity in the House
    • 22. 19.3 Safe Use of Electricity in the House
      • Fuse
      • A safety device that protects the wiring and thus protect us
      • Fuse melts and breaks when current exceeds its specific value
      • Fuse ratings are 3 A, 5 A and 13 A
      • Choose fuse which can take current slightly larger than maximum current allowable
    • 23. 19.3 Safe Use of Electricity in the House
    • 24. 19.3 Safe Use of Electricity in the House
    • 25. 19.3 Safe Use of Electricity in the House
      • Lighting Circuits
      • Each circuit has its own fuse in the consumer unit
    • 26.
      • Switches
      • Used to turn an electrical appliance on or off
      • Used as a safety device to cut off flow of current in event someone accidentally touch a live wire and gets an electric shock
      • Two way switches can be used to control a single lamp
      19.3 Safe Use of Electricity in the House
    • 27. 19.3 Safe Use of Electricity in the House
      • The Earth Wire
      • Serves as safety device
      • Joined to metal case of appliance
      • If live wire touches case, large current will flow to the Earth and blow fuse in live wire
      • Avoids electric shock
    • 28.
      • Double Insulation
      • Double insulation is the shielding and isolation of live electrical components
      • Used in electrical appliances which are not earthed
      • Appliances have 2-pin plug: live and neutral wire
      • Examples: hair dryer, electric shavers, battery charger, television sets
      • Casing made of plastic, wire cannot touch casing even if it become loose as there is double insulation
      19.3 Safe Use of Electricity in the House
    • 29. 19.3 Safe Use of Electricity in the House
      • Three-Pin Plugs
      • Live wire: brown
      • Neutral wire: blue
      • Earth wire: yellow and green stripes
    • 30.
      • Switches, fuses or circuit breakers must always be inserted along ‘live’ wires of circuits
      • When switch is off or the fuse has ‘blown’, the ‘live’ wire is disconnected from the high voltage
      19.3 Safe Use of Electricity in the House
    • 31.
      • Household wiring systems include lighting circuits and power circuits
      • A power circuit consists of a live wire, a neutral wire and an earth wire
      • Earthing metal cases and double insulation serve as safety devices
      • Circuit switches, fuses and circuit breakers also serve as safety devices
      • Circuit switches, fuses and circuit breakers must be connected on the ‘live’ side of a wiring system
      • The wires in a three-core cable must be connected correctly to their corresponding pins
    • 32.  
    • 33.
      • What is the difference between power and energy?
      • How do you calculate the cost of using electrical energy?
      • What safety features are designed into electric circuits?
      Questions
    • 34.  
    • 35.  
    • 36.  
    • 37.  
    • 38.  

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