N1 Engineering Science|The Easy Way! 119 6.12.12 Relay in a circuit


Fig. 6.17 shows a circuit diagram of a relay switch (also known as a solenoid switch) used for starter circuits of motor cars. When the starter switch is closed (primary circuit – low current) the relay contacts close (secondary circuit – high current). With the secondary circuit closed, the starter motor is operated.


On opening the starter switch, the relay contacts also open.


By using this relay switch, the length of the thick, high-current wire is shortened, and the necessity of a large bulky switch to operate the starter motor circuit (which draws a relatively high current) is eliminated.


Fig. 6.17 Starter motor circuit (for a motor car) Exercise 6.1


1. How would you define a conductor? 2. When electrons “drift” ormove in a specific direction, what is actually taking place? 3. What is the best conductor material? 4. What is the purpose of a conductor? 5. What are the two most commonly used conductor materials for electric cables? 6. Explain what you understand by electrical current. 7. Which is a better conductor, gold or copper? 8. Define an insulator. 9. What is PVC used for in an electric circuit? 10. Give a practical example where PVC is used. 11. What do the abbreviations ac and dc represent? 12. What is the difference between ac and dc? 13. What type of current is obtained from a battery? 14. What type of electricity is supplied to your house? 15. What is the most common source of dc? 16. What type of electricity would you say is portable? Give an example.


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