Practical electricity

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Secondary 3 Combined Science Physics

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Practical electricity

  1. 1. Recap! Electrical Energy
  2. 2. Example 1 A 24 ohm resistor is to be connected in series with a 12V battery. What is the power loss in the resistor? Hint : Solve using V=IR & P=IV
  3. 3. Example 2 A Lamp has a power rating of 100w and was used for 5 hrs. A cooker has a power rating of 3kW and was used of 0.5 hrs. What was the cost for the total usage of both the appliances if the cost of a unit (kWH) of electricity is $0.10?
  4. 4. Practical Electricity Dangers of Electricity
  5. 5. Types of Dangers Overheating of Cables Damp Environments Damaged Insulation • Overloaded power sockets cause large current flow • Use of inappropriate wires may result in overheating • Insulating materials can become worn with time exposing the conducting wires. • Conducting wires can cause shocks if touched • Water is a good conductor of electricity and it can act as a conducting path for currents if in contact with uninsulated parts of electrical wires
  6. 6. Safety Features at Home • Circuit Breakers • Fuses • Switches • Earthing • Three-pin Plugs • Double Insulation
  7. 7. Circuit Breakers • circuit when a current that flows through them is too large • Live wires are connected to circuit breakers to ensure that the circuit breaker will trip andcut off supply to the appliance Switch off electrical supply in a
  8. 8. Switches • • Switches should to connected to live wires to prevent electric shock in case of electrical faults
  9. 9. • Live Wire (Brown) is connected to high voltage & delivers current • Neutral Wire (Blue) completes the circuit by providing a return path to the supply for the current • Earth Wire (Green & Yellow) is of low resistance so that current can Earthing
  10. 10. Earthing
  11. 11. Fuses • Acts similarly to circuit breakers, preventing excessive current flow • However, instead of tripping, fuses blow and have to replaced once the blow • Fuses have a thin wire, which overheats and melts creating an open circuit. All fuses come with a rating which indicates maximum current that is allowed to flow through before the fuse blows
  12. 12. Calculation involving Fuses Example Qn A iron is rated at 1740W & 240V. What would be the current required for the iron to operate? What would be a suitable fuse rating to protect the iron from overheating? Using P=VI, I= P/V = 1740/240 = 7.25A Therefore, a fuse slightly larger than the current flowing
  13. 13. Three-Pin Plug • Fuse protects the appliance when there is an electrical fault • When excessive current flows through, the fuse blows, breaking the circuit so that it does not overheat the appliance and damage it
  14. 14. Double Insulation • Electric cables are insulated from the internal components • Internal components are insulated from external casing • Usually cased in non-metallic materials
  15. 15. Homework!

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