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Physics of Circuits

Physics of Circuits. Created for BW Physics Middle School Science Teachers By Dick Heckathorn 23 April 2K + 8. Equipment. 1. Meter 2. Resistors 3. Battery 4. Connecting Wire. Table of Contents. 4 A. Finding Total or Equivalent Resistance of Resistors in Series

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Physics of Circuits

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

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

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

  4. A. Finding Total or Equivalent Resistanceof resistors connectedinSeries

  5. R1 R3 R2 • 1. Measure and record the resistance of three resistors. _______ _______ _______

  6. _______ _______ R1 + R2 R1 + R3 R2 + R _______ • 2. Connect two of the resistors end to end (in series) and measure the resistance across each pair.

  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. R1 + R2 • 4. Develop a rule from which you can predict the equivalent resistance of two resistors in series. R1 + R3 R2 + R3

  9. R1 + R2 + R3 • 5. Connect all three resistors end to end and measure the resistance across all three. _____________

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

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

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

  13. R3 R2 _________ _________ _________ R1 • 1. Record the resistance of the three resistors that you measured before.

  14. R1 : R2 R2 : R3 _________ _________ _________ R1 : R3 • 2. Connect two of the resistors as shown (in parallel) and measure the resistance across each end.

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

  16. R1 : R2 : R3 ____________ • 4. Connect all three resistors as shown, then measure the resistance across all three.

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

  19. C. Circuit Analysis One Resistor

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

  21. A VA VR VB Measure and record: I R Voltage VA Voltage VB Current I Voltage VR

  22. A VA VR VB Conclusion(s) I R I? VB,I,andR? VB,I,andR? Compare VBwithVA and VR and Compare VBwithVA and VR and

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

  24. VR VB 8. Remove Ammeter R

  25. VR VB 9. Connect and measure the voltage across the battery and then the resistor. Record the values. R VR = _______ VB = _______

  26. VR VB Conclusion(s)? R How do VB and VR compare?

  27. 10. Calculate: How do they compare?

  28. 11. What does your instructor say about this? • Your instructor says that VBand VRshould be the same as the energy per charge given to the electrons by the battery VB and then removed by the resistor VR.

  29. D. Circuit AnalysisTwo ResistorsConnected in Series

  30. 1. Measure the value of two resistors. R1 = _________ R2 = _________ Then construct the following circuit.

  31. A R1 R2 2. Measure and record the current. I = ____________

  32. A I R1 VB V1 V2 R2 3. Measure and record the voltage across the battery and both of the resistances. VR2 = _______ VR! = _______ VB = _______

  33. 4. How does VB compare to VR1 and VR2? • 5. Calculate VR1/R1 and VR2/R2 • ______ ______ • What do these values compare to?

  34. 5. Calculate both VR1/R1 and VR2/R2. How do they compare? What do these values compare to?

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

  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 (VB) supplied by the battery equals the sum of the potential difference (V1+V2) lost in the components connected in series.

  37. E. Circuit AnalysisTwo ResistorsConnected in Parallel

  38. 1. Measure the value of both resistor. R1 = _______ R2 = _______ Then construct the following circuit.

  39. A I R2 R1 2. Record the value of the current IT= ________

  40. A1 I2 I1 A2 R2 R1 3. If you have access to two meters, create the circuit below and measure the current through both resistors. Otherwise, hook up A1 measure the current I1 and then repeat for A2.

  41. A1 I2 I1 A2 R2 R1 Measure and record both currents. IR1 = ____________ IR2 = ____________

  42. A1 IR2 IR1 AR2 R2 R1 4. How is the does the current through each meter, IR1 and IR2 compare to the total current IT? IT = _______IR1 = _______ IR2 = _______

  43. R2 R1 5. Remove all ammeters which will give you the following circuit.

  44. VB VR2 VR1 R2 R1 6. Measure and record the voltage across the battery VB, and the voltage across the two resistors VR1 and VR2 VB_______ VR1_______ VR2_______

  45. 7. How is the voltage of the battery VB related to the voltage through each resistor VR1 and VR2? • VB_______ VR1_______ VR2_______ • Calculate the following:

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

  47. Summary • 1. Current (I) from the battery equals the sum of the currents (I1+ I2) through the separate resistances. • 2. Potential difference (VB) supplied by the battery equals the potential difference (V1 = V2) lost in the resistances connected in parallel.

  48. Final Summarywith some problems

  49. 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.

  50. 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.

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