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Circuit 2

Power 1. Circuit 2. Next Slide. Basic Definitions. Power : the rate at which energy is transferred from one form to another. By considering the Ohm’s law, electrical power is. Power 2. Circuit 2. Next Slide. Domestic circuit. Label on domestic electrical equipment : (e.g. “12V 24W).

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Circuit 2

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  1. Power 1 Circuit 2 Next Slide Basic Definitions • Power : the rate at which energy is transferred from one form to another • By considering the Ohm’s law, electrical power is

  2. Power 2 Circuit 2 Next Slide Domestic circuit • Label on domestic electrical equipment : • (e.g. “12V 24W) • Example Calculation • Electrical power rating for common electrical appliance. Table

  3. Domestic circuit 1 Circuit 2 Next Slide Domestic circuit • Direct current (d.c.) and Alternating current (a.c.) • Frequency (50 Hz) and e.m.f. (220 V) of a.c. used in Hong Kong • Electrical cable • Live wire, Neutral wire and Earth wire Photo • Wiring inside an iron Diagram

  4. Domestic circuit 2 Circuit 2 Next Slide Domestic circuit • Household electric wiring plan Photo • Ring circuit Diagram • Lamp on a staircase Diagram • Safety Rules

  5. END of Circuit 2

  6. Power 2 Circuit 2 Next Slide • A lamp has a label “200 V 100 W” (a) What is the resistance of the lamp? (b) What is the current passing through the lamp under normal operating p.d.? (c) What is the electrical power of the lamp if a p.d. 100 V is applied across the lamp?

  7. Back to Power 2 Circuit 2 Click Back to

  8. Back to Power 2 Circuit 2 Click Back to • A table of electrical power rating for common electric appliance : Appliance Power rating (W) Fan 150 Iron 1000 Kettle 2000 Television 100 Washing machine 500 Water heater 3000

  9. Domestic circuit 1 Circuit 2 Next Slide • Three-hole socket and three-pin plug are shown in the following photos.

  10. Domestic circuit 1 Circuit 2 Next Slide

  11. Back to Domestic circuit 1 Circuit 2 Click Back to • Live wire (brown) : its potential is varying between +ve and -ve as a.c. Hence, the current is made to flow backwards and forwards through the circuit. • Neutral wire (blue) : completes the circuit by providing path for the current to flow. It is earthed and its potential is 0. • Earth wire (green & yellow) : connects the metal body of the electrical appliance to the earth to act as a safety device.

  12. switch fuse live 200 V a.c. (50 Hz) neutral earth Domestic circuit 1 Circuit 2 Next Slide • In the following figure, an iron is used as an example to show the wiring inside an electrical appliance.

  13. current earth with earth wire without earth wire Back to Domestic circuit 1 Circuit 2 Click Back to • Switch should be fitted in the live wire, not the neutral wire. • Fuse : a thin wire which melts and opens the circuit if the current exceeds a specified value. • The function of earth wire is shown in the following diagram

  14. Back to Domestic circuit 2 Circuit 2 Click Back to • A household electric wiring plan is shown below.

  15. Domestic circuit 2 Circuit 2 Next Slide • Ring circuit : Each of the live, neutral and earth wire of the cable forms a ‘ring’ and the mains sockets are connected to them. • An advantage of the ring main is that the current to each socket flows through 2 paths and the danger of over heating in the wires could be avoided even thinner wires are used. • All the sockets are connected to this ring main circuit in parallel pattern. If one of the sockets is damaged, other sockets would not be affected.

  16. live wire neutral wire Back to Domestic circuit 2 Circuit 2 Click Back to

  17. 2-way switch 2-way switch Back to Domestic circuit 2 Circuit 2 Click Back to • Lamp on a staircase : Two-way switches are connected as shown in the following figure. To complete the circuit the switches must either be both up or both down. If they are at opposite positions, the lamp is switched off. Therefore, the lamp could be controlled by both switches.

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