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

2 Equipment with Schematic Symbols 1.Meters 2.Resistors 3.Battery 4.Connecting Wire 5.Connecting Wire with Clips A Ammeter Voltmeter V Resistor Battery

Voltmeter Ammeter with leads connected

4 Table of Contents 44A.Finding Total or Equivalent Resistance of Resistors in Series 1212B.Finding Total or Equivalent Resistance of Resistors in Parallel 1919C.Circuit Analysis One Resistor 2929D.Circuit Analysis Two Resistors Connected in Series 3838E.Circuit Analysis Two Resistors Connected in Parallel 4949Final Summary with Some Problems 6464Connecting a 3-Way Switch

Current Meter Connections Common Jack Black Lead Voltage Resistance

Units Current (amp) charge/time Voltage (Volts) energy/time Resistance (ohm) opposition

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

R in series

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

2 R in Series

11 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 _______

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

13 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

3 R in series

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

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

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

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

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

2 R in Parallel

21 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 _________

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

3 R in Parallel

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

Carry Electrical Problem Homework Assignment NDSL 25

26 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 ___

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

28 C.Circuit Analysis One Resistor 138

29 A R 1.Measure the value of a resistor. R = ___ Next construct the following circuit. Now, set the ammeter to 10 amp. Finally complete the curcuit.

Resistor with Amp Meter Circuit 30 A R

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

32 VBVB Measuring Voltge of Battery A I R I? V B = ________

33 VRVR Measuring Voltage across R A I R V R = ________

34 VAVA VRVR VBVB Measuring Voltage across Meter A I R V A = ________

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

36 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.

37 VRVR VBVB 8.Remove Ammeter R

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

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

40 10.Calculate: This is the same as the ___________.

41 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.

42 D.Circuit Analysis Two Resistors Connected in Series

43 1.Measure the value of two resistors. R 1 = _________ R 2 = _________ Then construct the following circuit. A R1R1 R2R2

Batt+A+2 R in Series A R1R1 R2R2

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

46 3.Measure and record the voltage across the battery and both of the resistances. V B = _______ VBVB V1V1 V2V2 A I R1R1 R2R2 V R1 = _______ V R2 = _______

Batt + 2R + Vr +Vr+2R in series

Batt+Vbatt+A+2R series

50 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?

51 5.Calculate both V R1 /R 1 and V R2 /R 2. What do these values compare to? Current? Yes How do they compare? Are Equal? Yes

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

53 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.

54 Conclusion(s) VBVB V1V1 V2V2 A I R1R1 R2R2 Compare V B with V R1 and V R2 Compare: V B, I, and R 1 + R 2 ?

7. V B should equal: V R1 + V R2 V B should equal: I x (R 1 + R 2 ) 55

56 7.What does your instructor say about this? Resistance in Series 1.Current (I) in the circuit is everywhere the same. 2.Energy per charge supplied by the battery (VB) equals the sum of the energy per change (V1+V2) lost in the components connected in series.

Apr 17 57

58 E. Circuit Analysis Two Resistors Connected in Parallel

59 1.Measure the value of two resistors. R 1 = _______ R 2 = _______ Then construct the following circuit. A I R1R1 R2R2

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

61 A2A2 A1A1 R1R1 R2R2 I R1 I R2 3.Construct the circuit below.

62 I R1 = ____________ I R2 = ____________ Measure and record both currents. R1R1 R2R2 A1A1 I R1 A2A2 I R2

63 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 ? R1R1 R2R2 A1A1 I R1 A2A2 I R2

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

Batt + A + 2R in parallel

66 6a.Measure and record the voltage across the battery V B. V B _______ VBVB R1R1 R2R2

Batt+Vbatt+A+2R parallel

68 6b.Measure and record the voltage V R1 V R1 _______ V R1 R1R1 R2R2

Batt+A+Vr’s+2R in parallel

70 6c.Measure and record the voltage V R2 V R2 _______ V R2 R1R1 R2R2

71 6.The voltage values are: V B _______ V R1 _______ V R2 _______ VBVB V R1 V R2 R1R1 R2R2

72 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:

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

74 Summary 1.Current (I) from the battery equals the sum of the currents (I 1 + I 2 ) through the separate resistors. 2.Potential difference (V B ) of the battery equals the potential difference across each resistor. (V 1 = V 2 )

75 Special Project I T _______ I R1 _______ I R2 _______ VBVB V R1 R1R1 R2R2 1 A1A1 I R1 A2A2 I R2 A3A3 I3I3 V B _______ V R1 _______ V R2 _______ V R2 V3V3

76 A Summary with some problems

77 Summary What governs the amount of electric energy an electron will lose in each resistor? The conservation of energy. The amount of energy lost (equal to the sum of the energy lost in the 2 resistors) is the same as the energy supplied by the battery.

78 Summary What governs the number of electrons that will take each path? The conservation of charge. There is no gain or loss of electrons from one region to anoher. The current supplied by the battery is equal to the sum of the current through each resistor.

79 Series Circuit R1R1 R2R2 R3R3 VTVT V1V1 V2V2 V3V3

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

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

82 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

83 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:

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

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

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

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

88 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

89 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

90 That’s all folks!

Electrical Transmission

12,000 V 240,000 V 2400 V 240 V Energy Transmission The voltage is increased to reduce the energy lost as it is transferred through the wires over a long distance. The voltage must then be reduced to a value that is acceptable for home usage.

3-Way Switch Connection

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