ELECTRICITY & MAGNETISM - EXAMINATION QUESTIONS (4)

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1 ELECTRICITY & MAGNETISM - EXAMINATION QUESTIONS (4) 1. Which two electrical quantities are measured in volts? A current and e.m.f. B current and resistance C e.m.f. and potential difference D potential difference and resistance 2. Which of the following pieces of copper wire has the greatest electrical resistance? 3. A 20Ω resistor and a 10Ω resistor are connected in parallel. What is their combined resistance? A less than 10Ω B 10Ω C 20Ω D more than 20Ω 4. Why are the electric lamps in a house lighting circuit normally connected in parallel? A The current in every circuit must be the same. B The lamps are always switched on and off at the same time. C The voltage across each lamp must be the mains voltage. D When one of the lamps blows, all the others go out. 5. (a) Two non-conducting spheres, made of different materials, are initially uncharged. They are rubbed together. This causes one of the spheres to become positively charged and one negatively charged. Describe, in terms of electron movement, why the spheres become charged (b) Once charged, the two spheres are separated, as shown in Fig On Fig. 7.1, draw the electric field between the two spheres. Indicate by arrows the direction of the electric field lines. (c) A conducting wire attached to a negatively charged metal object is connected to earth. This allows electrons, each carrying a charge of C, to flow to earth in s. Calculate (i) the total charge that flows, charge... MR. HOSSAM SAMIR Page 1

2 (ii) the average current in the wire. current In which circuit does the ammeter read the total current through both resistors? 7. The table shows the voltage and current ratings for four light bulbs. Which bulb has the greatest resistance when used normally? 8. The diagram shows a circuit, with four possible positions to place a switch. At which labelled point should a switch be placed so that lamp 1 remains on all the time and lamp 2 can be switched on and off? MR. HOSSAM SAMIR Page 2

3 9. A classroom has four lights, each fitted with a lamp marked 240 V, 100 W. Which circuit is most suitable for the classroom? 10. Fig. 8.1 shows a battery with a resistor connected across its terminals. The e.m.f. of the battery is 6.0V. The battery causes 90 C of charge to flow through the circuit in 45 s. (a) Calculate (i) the current in the circuit, current =... (ii) the resistance of the circuit, resistance =... (iii) the electrical energy transformed in the circuit in 45 s. energy =... (b) Explain what is meant by the term e.m.f. of the battery Fig shows a battery with an e.m.f of 12 V supplying power to two lamps. The total power supplied is 150W when both lamps are on. (a) Calculate the current supplied by the battery when both lamps are on. current =... (b) The current in lamp L2 is 5.0 A. Calculate (i) the current in lamp L1, current =... (ii) the power of lamp L1, power =... (iii) the resistance of lamp L1. resistance =... MR. HOSSAM SAMIR Page 3

4 12. (a) Fig. 3.1 shows the scale of an ammeter. Draw the position of the pointer when the ammeter reading is 0.35 A. (b) The ammeter was used in the circuit shown in Fig. 3.2 to investigate the current in a lamp. (i) Name the component labelled Y.... (ii) The table shows the current I in the lamp for different values of the p.d. V across the lamp. 1. Calculate the values for the resistance R of the lamp, using the equation R = V / I Write your answers in the table. 2. Complete the column headings in the table. (iii) Suggest how the value of V could be varied (c) Fig. 3.3 shows a power source connected to three resistors labelled X, Y and Z. Complete the diagram to show (i) a voltmeter connected to measure the voltage across the resistors, (ii) an ammeter connected to measure the current in resistor X only, (iii) connecting wires to complete the circuit. MR. HOSSAM SAMIR Page 4

5 13. A student wants to find the resistance of resistor R using a voltmeter and an ammeter. Which circuit should the student use? 14. Two very light, charged balls P and Q are hung, one above the other, from nylon threads. When a negatively charged plastic sheet is placed alongside them, P is repelled and Q is attracted. What are the original charges on P and on Q? 15. A 3.0Ω lamp and a 6.0Ω lamp are connected in series. What is the total resistance of the combination? A 0.5Ω B 2.0Ω C 9.0Ω D 18.0Ω 16. Which electrical component would not normally be found in a battery-operated torch (flashlight)? MR. HOSSAM SAMIR Page 5

6 17. The diagrams show two ways in which three lamps may be connected. Which statement is correct? A If lamp Y breaks in circuit 1, both the other lamps will go out. B If lamp Y breaks in circuit 2, both the other lamps will go out. C If lamp Y breaks in circuit 1, lamp Z will go out, but lamp X will remain on. D If lamp Y breaks in circuit 2, lamp Z will go out, but lamp X will remain on. 18. A student connects two lamps in the circuit shown. Which switches must he close to light both lamps? A 1 and 2 B 1, 2 and 3 C 1 and 3 D 2 and Fig. 8.1 shows a 240 V a.c. mains circuit to which a number of appliances are connected and switched on. (a) Calculate the power supplied to the circuit. power =. (b) The appliances are connected in parallel. (i) Explain what connected in parallel means (ii) State two advantages of connecting the appliances in parallel rather than in series. advantage 1... advantage 2... MR. HOSSAM SAMIR Page 6

7 (c) Calculate (i) the current in the refrigerator, current =.. (ii) the energy used by the fan in 3 hours, energy =.. (iii) the resistance of the filament of one lamp. resistance = Fig. 7.1 shows a 12 V battery connected to a number of resistors. (a) Calculate the current in the 8Ω resistor. current =.. (b) Calculate, for the resistors connected in the circuit, the combined resistance of (i) the two 5Ω resistors, resistance =.. (ii) the two 4Ω resistors. resistance =.. (c) The total current in the two 4Ω resistors is 6 A. Calculate the total power dissipated in the two resistors. power =.. (d) What will be the reading on a voltmeter connected across (i) the two 4Ω resistors, reading =.. (ii) one 5Ω resistor? reading =.. (e) The 8Ω resistor is made from a length of resistance wire of uniform cross-sectional area. State the effect on the resistance of the wire of using (i) the same length of the same material with a greater cross-sectional area,... MR. HOSSAM SAMIR Page 7

8 (ii) a smaller length of the same material with the same cross-sectional area A circuit is set up with a gap between two terminals X and Y. The four strips of material shown in the diagram are connected in turn across the gap. Which strip completes the circuit so that the lamp lights? 22. A pupil measures the potential difference across a device and the current in it. Which calculation gives the resistance of the device? A current + potential difference B current potential difference C potential difference current D potential difference x current 23. Which circuit could be used to find the resistance of resistor R? 24. In which position in the circuit shown should a switch be placed so that both lamps can be switched on or off at the same time? MR. HOSSAM SAMIR Page 8

9 25. In the circuits shown, all the resistors are identical. Which circuit has the least resistance? 26. In the circuit shown, the reading on ammeter 1 is 2 A. What is the reading on ammeter 2? A) 0 A B)1 A C) 2 A D) 4 A 27. Why are electric circuits often fitted with fuses? A Fuses break the circuit if the current is too high. B Fuses only allow the current through in the correct direction. C Fuses return any excess current to earth. D Fuses use up any spare current. MR. HOSSAM SAMIR Page 9

10 28. A mains circuit can safely supply a current of 40 A. A hair-drier takes 2 A. It is connected to the circuit by a lead which can carry up to 5 A. Which of these fuses would be best to use in the plug fitted to the hair-drier lead? A) 1 A fuse B) 3 A fuse C) 10 A fuse D) 50 A fuse 29. A polythene rod repels an inflated balloon hanging from a nylon thread. What charges must the rod and the balloon carry? A The rod and the balloon carry opposite charges. B The rod and the balloon carry like charges. C The rod is charged but the balloon is not. D The balloon is charged but the rod is not. 30. Which circuit shows how a voltmeter is connected to measure the potential difference across the cell? 31. An electrical component is to be placed in the circuit at Z, to allow the brightness of the lamp to be varied from bright to dim. What should be connected at Z? 32. Fig. 3.1 shows the circuit that a student uses to find the resistance of a combination of three lamps. The voltmeter and the ammeter have not been drawn in. (a) Complete Fig. 3.1 by drawing in the voltmeter and the ammeter, using conventional symbols. (b) The student obtains these readings. current I = 0.54 A potential difference V = 1.8 V Calculate the resistance R using the equation R = V / I R =... The three lamps are now connected in parallel with one another. Draw a circuit diagram of the three lamps connected to the power supply. Include in your circuit diagram (i) an ammeter to record the total current through the lamps, (ii) a variable resistor to vary the brightness of all three lamps, (iii) a voltmeter to record the potential difference across the lamps. 33. The circuit shown contains four lamps and three switches. MR. HOSSAM SAMIR Page 10

11 Which switches must be closed to light only lamps 1 and 3? A switch 1 only B switch 1 and switch 2 only C switch 1 and switch 3 only D switch 2 and switch 3 only 34. The diagram shows a torch containing two 2 V cells, a switch and a lamp. What is the circuit diagram for the torch? 35. A student has a power supply, a resistor, a voltmeter, an ammeter and a variable resistor. (a) The student obtains five sets of readings from which he determines an average value for the resistance of the resistor. In the space below, draw a labelled diagram of a circuit that he could use. (b) Describe how the circuit should be used to obtain the five sets of readings (c) Fig. 8.1 shows another circuit. When the circuit is switched on, the ammeter reads 0.50 A. MR. HOSSAM SAMIR Page 11

12 (i) Calculate the value of the unknown resistor. resistance =. (ii) Calculate the charge passing through the 3.0Ω resistor in 120 s. charge =. (iii) Calculate the power dissipated in the 3.0Ω resistor. power =. 36. In the circuit below, X and Y are identical 6 V lamps. What happens when the switch is closed? A X lights more brightly than Y. B Y lights more brightly than X. C X and Y light with equal brightness. D Neither X nor Y light. 37. The diagram shows a circuit with three ammeters, X, Y and Z. Which set of readings is possible? 38. Which statement is correct? A A fuse is included in a circuit to prevent the current becoming too high. B A fuse should be connected to the neutral wire in a plug. C An electric circuit will only work if it includes a fuse. D An earth wire is needed to prevent the fuse blowing. 39. Fig. 8.1 shows a high-voltage supply connected across two metal plates. When the supply is switched on, an electric field is present between the plates. MR. HOSSAM SAMIR Page 12

13 (a) Explain what is meant by an electric field.... (b) On Fig. 8.1, draw the electric field lines between the plates and indicate their direction by arrows. (c) The metal plates are now joined by a high-resistance wire. A charge of C passes along the wire in 30 s. Calculate the reading on the ammeter. ammeter reading = (d) The potential difference of the supply is re-set to 1500 V and the ammeter reading changes to A. Calculate the energy supplied in 10 s. Show your working. energy =. 40. Which circuit should be used to find the resistance of a lamp? 41. The table shows the voltage and current ratings for four electric heaters. Which heater has the least resistance? 42. Why are the electric lamps in a house lighting circuit normally connected in parallel? A The current in every circuit must be the same. B The lamps are always switched on and off at the same time. C The voltage across each lamp must be the mains voltage. D When one of the lamps blows, all the others go out. MR. HOSSAM SAMIR Page 13

14 43. When the circuit shown is connected with switch S open, the 6 V lamp glows. What happens to the brightness of the lamp when switch S is closed? A It becomes brighter. B It remains the same. C It becomes dimmer. D It goes off. 44. A lamp is to be connected in a circuit so that the p.d. across it can be varied from 0 to 6 V. Which circuit would be most suitable? 45. Fig. 8.1 shows part of a low-voltage lighting circuit containing five identical lamps. MR. HOSSAM SAMIR Page 14

15 (a) Complete the circuit, by the addition of components as necessary, so that (i) the total current from the supply can be measured, (ii) the brightness of lamp E only can be varied, (iii) lamps C and D may be switched on and off together whilst lamps A, B and E remain on. (b) All five lamps are marked 12 V, 36 W. Assume that the resistance of each lamp is the same fixed value regardless of how it is connected in the circuit. Calculate (i) the current in one lamp when operating at normal brightness, current =... (ii) the resistance of one lamp when operating at normal brightness, resistance =... (iii) the combined resistance of two lamps connected in parallel with the 12 V supply, resistance =... (iv) the energy used by one lamp in 30 s when operating at normal brightness. energy =... (c) The whole circuit is switched on. Explain why the brightness of lamps A and B is much less than that of one lamp operating at normal brightness Fig. 8.1 shows two electrical circuits. The batteries in circuit 1 and circuit 2 are identical. (a) Put ticks in the table below to describe the connections of the two resistors P and Q. (b) The resistors P and Q are used as small electrical heaters. MR. HOSSAM SAMIR Page 15

16 State two advantages of connecting them as shown in circuit 2. advantage 1... advantage 2... (c) In circuit 1, the ammeter reads 1.2 A when the switch is closed. Calculate the reading of the voltmeter in this circuit. voltmeter reading =... (d) The two switches in circuit 2 are closed. Calculate the combined resistance of the two resistors in this circuit. combined resistance =... (e) When the switches are closed in circuit 2, ammeter 1 reads 5 A and ammeter 2 reads 2 A. Calculate (i) the current in resistor P, current =... (ii) the power supplied to resistor Q, power =... (iii) the energy transformed in resistor Q in 300 s. energy = Three charged balls, P, Q and R, are suspended by insulated threads. Ball P is negatively charged. What are the charges on Q and on R? 48. The circuit shows a current I in a resistor of resistance R. Which line gives possible values of I and of R? MR. HOSSAM SAMIR Page 16

17 49. Four lamps are connected in a circuit as shown in the diagram. Each lamp is designed to operate at 12 V. The circuit is now switched on. Which statement is correct? A Each lamp can be switched off independently. B If one lamp breaks all the others will stay alight. C The current is the same in all the lamps. D The lamps will all light at normal brightness. 50. The diagram shows a battery connected to three identical resistors. Four ammeters A, B, C and D are connected in the circuit. Which ammeter shows the smallest reading? 51. In the circuit shown, the switch is closed for a long time, then opened. Immediately after the switch is opened, which voltmeters will read zero? A voltmeter 1 only B voltmeter 2 only C voltmeter 3 only D voltmeter 1, voltmeter 2 and voltmeter Four wires are made from the same material. Which wire has the greatest resistance? 53. A plastic rod is rubbed with a dry cloth and becomes positively charged. Why has the rod become positively charged? A It has gained electrons. B It has gained neutrons. C It has lost electrons. D It has lost neutrons. MR. HOSSAM SAMIR Page 17

18 54. Which diagram shows a circuit that will allow the lamps to be switched on and off independently? 55. The circuit shown in Fig uses a 12 V battery. (a) Switch S is open, as shown in Fig State the value of (i) the reading on the ammeter, reading =... (ii) the potential difference (p.d.) across S. p.d. =... (b) Switch S is now closed. (i) Calculate the current in the ammeter. current =... (ii) Calculate the p.d. across the 8 Ω resistor. p.d. =... (c) The two resistors are now connected in parallel. Calculate the new reading on the ammeter when S is closed, stating clearly any equations that you use. reading = In the circuit below, one of the lamps breaks, causing all the other lamps to go out. Which lamp breaks? MR. HOSSAM SAMIR Page 18

19 57. Fig. 8.1 is the plan of a small apartment that has four lamps as shown. Power for the lamps is supplied at 200 V a.c. and the lamps are all in parallel. (a) In the space below, draw a lighting circuit diagram so that there is one switch for each room and one master switch that will turn off all the lamps. Label the lamps as 60 W or 100 W. (b) The 100 W lamp is switched on. Calculate (i) the current in the lamp, current =... (ii) the charge passing through the lamp in one minute. charge =... (c) The three 60 W lamps are replaced by three energy-saving ones, that give the same light output but are rated at only 15 W each. Calculate (i) the total reduction in power, reduction in power =... (ii) the energy saved when the lamps are lit for one hour. energy saved = The diagram shows four different circuits. What is the order of increasing resistance of these circuits? MR. HOSSAM SAMIR Page 19

The rod and the cloth both become charged as electrons move between them.

1 polythene rod is rubbed with a cloth. polythene rod cloth The rod and the cloth both become charged as electrons move between them. The rod becomes negatively charged. Which diagram shows how the rod