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Equivalent Resistance

Equivalent Resistance. Series and Parallel Circuits. Two Kinds of circuits. Circuit Diagrams. When drawing pictures of circuits, symbols are used as shorthand instead of pictures of components. Circuit Diagrams. Instead of a battery, the symbol

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Equivalent Resistance

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  1. Equivalent Resistance Series and Parallel Circuits

  2. Two Kinds of circuits

  3. Circuit Diagrams • When drawing pictures of circuits, symbols are used as shorthand instead of pictures of components.

  4. Circuit Diagrams • Instead of a battery, the symbol is used. (Note: sometimes voltage is called emf or potential difference)

  5. Circuit Diagrams • Instead of a resistor, the symbol is used.

  6. Circuit Diagrams • Resistors and batteries will be labeled with their respective values most of the time. 10 Ω 10 Ω 9V

  7. Practice • Draw a series circuit with a 5V battery and two resistors (one 3Ω and the other 5Ω)

  8. Practice • Draw a series circuit with a 5V battery and two resistors (one 3Ω and the other 5Ω) 3Ω 5Ω 5V

  9. Practice • Draw a parallel circuit with a 12V battery and two resistors (one 6Ω and the other 2Ω)

  10. Practice • Draw a parallel circuit with a 12V battery and two resistors (one 6Ω and the other 2Ω) 6 Ω 2 Ω 12V

  11. Using Ohm’s Law (V=IR) • Ohm’s Law can be applied to A) the WHOLE circuit or B) each RESISTOR separately

  12. Ohm’s Law- WHOLE Circuit • What is Rtotal for the circuit? What is the current? 3Ω 5Ω 5V

  13. Ohm’s Law- WHOLE Circuit • Rtotal: • I: 3Ω 5Ω 5V

  14. Ohm’s Law- EACH Resistor • What is the voltage in each resistor? 3Ω 5Ω 5V

  15. Ohm’s Law- EACH Resistor • What do we know about the current in each resistor? 3Ω 5Ω 5V

  16. Ohm’s Law- EACH Resistor • What do we know about the current in each resistor? 3Ω 5Ω 5V

  17. Ohm’s Law- EACH Resistor • With that in mind we can solve for voltage. 3Ω resistor5Ωresistor 3Ω 5Ω 5V

  18. Ohm’s Law- EACH Resistor • With that in mind we can solve for voltage. 3Ω resistor5Ωresistor 3Ω 5Ω 5V

  19. Ohm’s Law- EACH Resistor • With that in mind we can solve for voltage. 3Ω resistor5Ωresistor 3Ω 5Ω 5V

  20. Ohm’s Law- EACH Resistor • Double check your answer to be sure. 3Ω resistor5Ωresistor 3Ω 5Ω 5V

  21. Summary- SERIES Circuits • We can write the ways we used Ohm’s Law as: Whole Resistor 1, Resistor 2, Resistor3, … Circuit

  22. Practice • Pg. 650 Practice A

  23. Ohm’s Law for PARALLEL circuits

  24. PARALLEL (WHOLE circuit) • To apply Ohm’s Law (V=IR) to the WHOLE circuit: V=10V 2Ω 4Ω 10V

  25. PARALLEL (WHOLE circuit) • To apply Ohm’s Law (V=IR) to the WHOLE circuit: V=10V 2Ω 4Ω 10V

  26. PARALLEL (WHOLE circuit) • To apply Ohm’s Law (V=IR) to the WHOLE circuit: V=10V Rtotal=1.33Ω I=? 2Ω 4Ω 10V

  27. PARALLEL (WHOLE circuit) • To apply Ohm’s Law (V=IR) to the WHOLE circuit: V=10V Rtotal=1.33Ω I=? V=IR → 10V=I(1.33Ω) 2Ω 4Ω 10V

  28. PARALLEL (WHOLE circuit) • To apply Ohm’s Law (V=IR) to the WHOLE circuit: V=10V Rtotal=1.33Ω I=7.51A 2Ω 4Ω 10V

  29. PARALLEL (EACH resistor) • Now find the CURRENT in each resistor. 2Ω 4Ω 10V

  30. PARALLEL (EACH resistor) • What do we know about VOLTAGE in a PARALLEL circuit? 2Ω 4Ω 10V

  31. PARALLEL (EACH resistor) • The VOLTAGE is the same everywhere… V= 10Volts everywhere… 2Ω 4Ω 10V

  32. PARALLEL (EACH resistor) • Now use V=IR to solve for current at each resistor: 2Ω resistor4Ωresistor 2Ω 4Ω V= 10V V= 10V 10V

  33. PARALLEL (EACH resistor) Total Circuit: V=10V Rtotal=1.33Ω I=7.51A Compare the currents 2Ω resistor4Ωresistor Equal + 2Ω 4Ω V= 10V V= 10V 10V

  34. Summary of Ohm’s Law • For PARALLEL circuits: • Vtotal=V1=V2=V3=… • Itotal=I1+I2+I3+… 2Ω 4Ω 10V

  35. Practice • Find • A) total resistance in circuit • B) current in each resistor 6Ω 2 Ω 12V

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