Chapter 5 – Electricity Sources and Supply, Electrostatics

1. Explain how static electricity can be produced.
2. What causes the build up of static electricity?
3. Define insulators and conductors.  Give examples of each.  Use your definitions to illustrate the differences between insulators and conductors.
4. Classify the following as insulators or conductors.

5. State which of the above materials cannot be charged by rubbing while being held in your hand.
6. What charge is gained if a material is rubbed and

   (a) Gains Electrons

   (b) Loses electrons

7. When ebonite is rubbed with cat’s fur, the fur becomes positive. What charge is on the ebonite?  Which way did the electrons move?
8. Use the table below to answer the following questions

(a)   Which materials have lost electrons after rubbing?

(b)   Which materials have gained electrons after rubbing?

(c)   List the substances, rubber, wool, ebonite and acetate, in order from strongest attracting power for electrons to weakest attracting power.

(d)   What further tests would you have to perform to be sure of the position of glass?

9. State the Law of Static electricity (Law of forces between charges)
10. An ebonite rod held in the hand becomes charged when rubbed with wool.  A brass sphere held in the hand and rubbed does not become charged

11. What would be the effect on the force of attraction or repulsion between two charged bodies if

(a)   The size of the charges was (i)     Increased (j)     Decreased?     

(b)   The distance between the bodies was (i)     Increased or (j)     Decreased?

12. Use the following table of relative electron-attracting powers of insulators to answer the questions below.

(a)   If acetate were rubbed with cat’s fur, which would gain electrons?

(b)   What two substances rubbed together would give the greatest build up of charge?(c)   If glass was

rubbed with silk, which would be positively charged?

(d)   If a glass rod was rubbed with cat’s fur and another glass rod was rubbed with silk would the glass rods repel or attract one another when held close together?

13. A student performs an electrostatic experiment with charged rods and other materials.  The results are tabulated below.

If rod A is negatively charged, what can we say about the charges of B, X, Y and Z?

14. A student tests a number of charged rods to see if they repel or attract each other.  Her incomplete table of results is shown below.  She has already proven that the charge on rod V is positive. Determine the charges on the other rods and complete the table.

15. What tests could you perform to check whether it was a suitable day to perform electrostatic experiments? 
16. What type of weather is ideal for electrostatic experiments?  Explain.
17. Rod A attracts rod B; rod C attracts rod B; rod A and C repel each other.  What can you deduce about the charges on the rods?
18.  What would happen if a suspend Perspex rod charged by rubbing with silk was brought close to another Perspex rod charged with silk?
19. Explain why tankers carrying flammable liquids often have a metal chain dragging along the ground.
20. A boy wipes his mirror with a dry cloth.  Shortly afterwards he notices that it is dusty again.  Explain what has happened.
21.  A nylon thread manufacturer placed thick rubber mats underneath the spinning machines to reduce the noise in the factory. Workers then complained that they often received an electric shock when touching the machines and that small pieces of fluff became attached to the nylon thread.  Explain why these things happened.  How could these problems be overcome?
22. Electroscopes can be used to determine whether an object is charged or not.  Use the diagrams below to explain how this apparatus works.

23. When a negatively charged rod is brought close to a positively charged electroscope, the leaves converge. Explain the behaviour of the leaves.
24. State some examples in which static electricity is an advantage.
25. Explain how lightning is produced.

Electricity from chemicals

26. Draw a diagram to show how an electric current can be produced using pieces of metals and a solution.         Label the electrodes and the electrolyte.
27. What conditions are necessary to produce an electric current?
28. What is meant by an electrolyte?
29. What happens if the electrodes are both of the same metal?
30. What instrument is used to measure the electrical energy produced by a simple chemical cell?
31. What energy conversion takes place in the simple chemical cell?
32. Why does a simple chemical cell eventually go ‘flat’?
33. What is polarisation?  What effect does it have on the current flowing from the cell?
34. What is the difference between a cell and a battery?
35. Determine from the following diagram which metal electrode is negative and which is positive.

36. Why is a ‘dry’ cell called dry?
37. What is the outer casing composed of?  What is the central positive electrode composed of?
38. What is the voltage of a common dry cell?
39. How can you increase the voltage using several dry cells?
40. How many dry cells are connected together in series to make a 9 Volt battery?
41. List the following in order from smallest to largest AAA, D, C, AA.  Which would last the longest when used to run the same torch bulb?
42. How can a rechargeable battery be recharged?  Give some examples of rechargeable batteries.
43. What are some applications of rechargeable batteries?
44. Why is it necessary to top up the water in a car battery?
45. Why is it unwise to light a match near a car battery while it is being recharged?
46. How is a car battery normally recharged?
47. Explain why a car battery eventually needs to be replaced.
48. Solar panels on isolated telephones use nickel-cadmium batteries.  Why are these batteries required?

Electricity produced by magnets

49. Explain how an electric current can be produced using a magnet and a coil of wire.
50. Explain the difference between AC and DC.
51. What are some ways that the current produced by a generator can be increased?
52. Why do power stations use electromagnets rather than normal magnets?
53. Why does a car need an alternator?
54. How is an alternator different from a generator? 

Revision Points

Electricity Test