1. 1 Physics of Circuits Created for BW Physics Middle School Science Teachers By Dick Heckathorn 23 April 2K + 8

2. 2 Equipment 1.Meter 2.Resistors 3.Battery 4.Connecting Wire

3. 3 Table of Contents 4A.Finding Total or Equivalent Resistance of Resistors in Series 12B.Finding Total or Equivalent Resistance of Resistors in Parallel 19C.Circuit Analysis One Resistor 29D.Circuit Analysis Two Resistors Connected in Series 38E.Circuit Analysis Two Resistors Connected in Parallel 49Final Summary with Some Problems 64Connecting a 3-Way Switch

4. 4 A.Finding Total or Equivalent Resistance of resistors connected in Series

5. 5 1.Measure and record the resistance of three resistors. _______ _______ _______ R2R2 R3R3 R1R1

6. 6 R 2 + R _______ 2.Connect two of the resistors end to end (in series) and measure the resistance across each pair. R 1 + R 2 _______ R 1 + R 3 _______

7. 7 3.A new resistor equal to the sum of the two resistors can replace the two resistors and has the same effect in a circuit as the two resistors. We call the sum, an equivalent resistance or a total resistance.

8. 8 4.Develop a rule from which you can predict the equivalent resistance of two resistors in series. R 1 + R 2 R 1 + R 3 R 2 + R 3

9. 9 5.Connect all three resistors end to end and measure the resistance across all three. R 1 + R 2 + R 3 _____________

10. 10 6.Does your rule for three resistors connected in series the same as for two resistors connected in series? Yes ___ No ___

11. 11 7.Your instructor hopes that you found the following to be true. Remember this is for ONLY resistors in series!

12. 12 B.Finding Total or Equivalent Resistance of Resistors in Parallel

13. 13 1.Record the resistance of the three resistors that you measured before. R1R1 _________ R2R2 R3R3

14. 14 2.Connect two of the resistors as shown (in parallel) and measure the resistance across each end. R 1 : R 2 _________ R 1 : R 3 _________ R 2 : R 3 _________

15. 15 3.Develop a rule from which can predict the equivalent resistance of two resistors in parallel?

16. 16 4.Connect all three resistors as shown, then measure the resistance across all three. R 1 : R 2 : R 3 ____________

17. 17 5.Is the rule for finding the equivalent resistance of three resistors connected in parallel the same for finding the equivalent resistance of two resistors connected in parallel? Yes ___ No ___

18. 18 6.The rule is: Remember this is ONLY for resistors in parallel!

19. 19 C.Circuit Analysis One Resistor

20. 20 A R 1.Measure the value of a resistor. R = ___ Set the ammeter to its greatest value. Then construct the following circuit.

21. 21 VRVR VBVB Measure and record: A Current I I R Voltage V R Voltage V B VAVA Voltage V A

22. 22 VAVA VRVR VBVB Conclusion(s) A Compare V B with V A and V R and I R V B, I, and R? I? Compare V B with V A and V R and V B, I, and R?

23. 23 6.Divide the voltage (V B ) by the resistance (R). 7.How does V B /R compare to the measured current? Be sure to keep track of units.

24. 24 VRVR VBVB 8.Remove Ammeter R

25. 25 VRVR VBVB R V B = _______ V R = _______ 9.Connect and measure the voltage across the battery and then the resistor. Record the values.

26. 26 VRVR VBVB Conclusion(s)? R How do V B and V R compare?

27. 27 10.Calculate: How do they compare?

28. 28 11.What does your instructor say about this? Your instructor says that V B and V R should be the same as the energy per charge given to the electrons by the battery V B and then removed by the resistor V R.

29. 29 D.Circuit Analysis Two Resistors Connected in Series

30. 30 1.Measure the value of two resistors. R 1 = _________ R 2 = _________ Then construct the following circuit.

31. 31 A R1R1 R2R2 2.Measure and record the current. I = ____________

32. 32 3.Measure and record the voltage across the battery and both of the resistances. V B = _______ VBVB V1V1 V2V2 A I R1R1 R2R2 V R! = _______ V R2 = _______

33. 33 4.How does V B compare to V R1 and V R2 ? 5.Calculate V R1 /R 1 and V R2 /R 2 ______ ______ What do these values compare to?

34. 34 5.Calculate both V R1 /R 1 and V R2 /R 2. What do these values compare to? How do they compare?

35. 35 6.Write a conclusion about the current and voltage in a circuit when two resistors are connected in series with the battery.

36. 36 7.What does your instructor say about this? Resistance in Series 1.Current (I) in the circuit is everywhere the same. 2.Potential difference (V B ) supplied by the battery equals the sum of the potential difference (V 1 +V 2 ) lost in the components connected in series.

37. 37 Conclusion(s) VBVB V1V1 V2V2 A I R1R1 R2R2 Compare V B with V A and V R Compare: V B, I, and R 1 + R 2 ?

38. 38 E. Circuit Analysis Two Resistors Connected in Parallel

39. 39 1.Measure the value of both resistor. R 1 = _______ R 2 = _______ Then construct the following circuit.

40. 40 A I R1R1 R2R2 2. Record the value of the current I T = ________

41. 41 A2A2 A1A1 R1R1 R2R2 I1I1 I2I2 3.If you have access to two meters, create the circuit below and measure the current through both resistors. Otherwise, hook up A 1 measure the current I 1 and then repeat for A 2.

42. 42 A2A2 A1A1 R1R1 R2R2 I1I1 I2I2 I R1 = ____________ I R2 = ____________ Measure and record both currents.

43. 43 A R2 A1A1 R1R1 R2R2 I R1 I R2 I T = _______ I R1 = _______ I R2 = _______ 4.How is the does the current through each meter, I R1 and I R2 compare to the total current I T ?

44. 44 5.Remove all ammeters which will give you the following circuit. R1R1 R2R2

45. 45 6.Measure and record the voltage across the battery V B, and the voltage across the two resistors V R1 and V R2 V B _______ V R1 _______ V R2 _______ VBVB V R1 V R2 R1R1 R2R2

46. 46 7.How is the voltage of the battery V B related to the voltage through each resistor V R1 and V R2 ? V B _______ V R1 _______ V R2 _______ Calculate the following:

47. 47 11.Write a conclusion about the current and voltage in a circuit where 2 resistors are connected in parallel with the battery.

48. 48 Summary 1.Current (I) from the battery equals the sum of the currents (I 1 + I 2 ) through the separate resistances. 2.Potential difference (V B ) supplied by the battery equals the potential difference (V 1 = V 2 ) lost in the resistances connected in parallel.

49. 49 Final Summary with some problems

50. 50 Summary What governs the amount of electric potential energy an electron will lose in each load? The conservation of energy. The amount gained is equal to the sum of the total energy lost.

51. 51 Summary What governs the number of electrons that will take each path? The conservation of charge. There is no gain or loss of electrons nor any accumulation at any point.

52. 52 Series Circuit R1R1 R2R2 R3R3 VTVT V1V1 V2V2 V3V3

53. 53 Resistance in Series 12 Ω, 25 Ω, and 42 Ω in series The equivalent resistance is 79 Ω

54. 54 Resistance in Series Three 30-Ω light bulbs and two 20-Ω heating elements connected in series The equivalent resistance is …. 130 ohms

55. 55 Resistance in Series two strings of Christmas tree lights connected in series, if the 1st string has eight 4-Ω bulbs & the 2nd has twelve 3-Ω bulbs The equivalent resistance is …. 68 ohms

56. 56 Resistance in Series a 20-Ω, a 18-Ω, and an unknown resistor are connected in series to give an equivalent resistance of 64-Ω 26 ohms Find the value of the unknown resistance in the following:

57. 57 Parallel Circuit R1R1 R2R2 R3R3 V1V1 V2V2 V3V3 VTVT I1I1 I2I2 I3I3 ITIT

58. 58 Find the equivalent resistance when a 4-Ω and an 8-Ω bulb are connected in parallel. 2.7 ohm Resistance in Parallel

59. 59 5.3 ohm Resistance in Parallel Find the equivalent resistance when a 16-Ω and an 8-Ω bulb are connected in parallel.

60. 60 2.9 ohm Resistance in Parallel Find the equivalent resistance when a 20-Ω, a 10- Ω and a 5-Ω bulb are connected in parallel.

61. 61 What resistance would have to be added in parallel with a 40- Ω hair dryer to reduce the equivalent resistance to 8- Ω? 10 ohm Resistance in Parallel

62. 62 30 Ω Resistance in Parallel Find the equivalent resistance of two, three, four, and five 60-Ω bulb are connected in parallel. 20 Ω 15 Ω 12 Ω Is there a simple relationship for the equivalent resistance of ‘n’ resistors in parallel? R/n

63. 63 That’s all folks!

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