130 Chapter 6 • Electricity Exercise 6.12
1. Make a neat sketch of a bar magnet illustrating the direction and shape of the magnetic lines of force.
2. Make a neat sketch of a current-carrying conductor showing the magnetic lines of force and their relative direction.
3. With the aid of a neat sketch, describe an experiment to show that magnetic lines of flux exist around a conductor when it carries a current.
4. With the aid of a neat sketch, describe the screw-rule method of determining the direction of the flux around a current-carrying conductor.
5. With the aid of a neat, simple sketch, show how a magnetic field is set up around a solenoid.
6. With the aid of a neat sketch, describe how the right-hand grip rule may be used to determine the polarity of an electromagnet.
7. Name three ways in which themagnetic flux of a solenoid can be strengthened.
8. Where could (a) a single stroke, and (b) a trembler bell be used? 9. With the aid of a neat sketch, describe the operation of a single stroke bell.
10. With the aid of a neat sketch, describe the operation of a trembler bell. 11. Why are the coils used in bells wound around an iron core? 12. Sketch a circuit diagramfor a bell controlled fromtwo different points.
13. What is the purpose of a relay switch? 14. Give a practical example of a relay switch. 15. With the aid of a neat, labelled sketch, explain the operation of a relay switch.
Summary 6.1
Conductors and current flow Conductors
Definition of a conductor A conductor is a substance through which electrical current can flow easily. • Copper wire is a good example of a conductor. • Conductors (wires) are used to carry current (electricity) fromone point to another. • Copper and aluminium are themost commonly used conductormaterials. • Silver is the best conductor, followed by copper, gold and aluminium. • Water as we know it (in an impure state), because of its fluidity, is a dangerous conductor. (Pure water can be classed as an insulator).
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