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Understanding DC Circuits: Key Concepts & Problem Solving

Learn about series and parallel circuits, Kirchhoff's rules, equivalent resistance, and more in physics lecture X. Test your knowledge with practice problems.

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Understanding DC Circuits: Key Concepts & Problem Solving

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  1. DC circuits Physics 122 Lecture X

  2. Test problem • For resistors connected in series, which of the following will be the same for each of the resistors? • A The current through. • B The potential difference across. • C The resistance of. • D The power dissipated by. Lecture X

  3. Test problem • For resistors connected in parallel, which of the following will be the same for each of the resistors? • A The current through. • B The potential difference across. • C The resistance of. • D The power dissipated by. Lecture X

  4. RC circuit • RC circuit contains at least one capacitor (C ) and at least one resistor (R ). +Q C -Q Lecture X

  5. Electric battery • For idealized battery emf – supplied voltage • Real life batteries have internal resistance r • Terminal voltage (supplied to the circuit) • Vab=emf-Ir Lecture X

  6. Kirchhoff’s rules • Junction rule (charge conservation): • At any junction point the sum of all current entering the junction must equal the sum of all currents leaving the junction • Do not disregard signs! • Assign initial signs based on your best guess – if you were wrong the currents will turn to be negative (opposite to initial guess) • Loop rule (energy conservation): • The sum of the changes in potential around any closed path of a circuit must be zero. • Choose a direction in which you circle the loop (random) • For resistor Vab=-IR – negative if current along the loop direction • For resistor Vab=+IR – positive if current opposite the loop direction • For battery Vab – positive if the direction is from – to + • For resistor Vab –negative if the direction is from + to - Lecture X

  7. Kirchhoff’s rules • Loop rule (energy conservation): • The sum of the changes in potential around any closed path of a circuit must be zero. • Choose a direction in which you circle the loop (random) • For resistor Vab=-IR – negative if current along the loop direction • For resistor Vab=+IR – positive if current opposite the loop direction • For battery Vab – positive if the direction is from – to + • For resistor Vab –negative if the direction is from + to - Lecture X

  8. R1=R2R R2=R3=R Req=3R4R R1=R2R R2=R3=R Req=R/3=2R/62R/5 Series vs parallel - Req If any of R’s increased the equivalent resistance will increase in both parallel and series connection. Lecture X

  9. R1=R2R R2=R3=R Req=3R4R I=V/Req=V/3RV/4R I1=I2=I3=I R1=R2R R2=R3=R Req=R/3=2R/62R/5 I=V/Req=6V/2R5V/2R I1=V/R1=V/RV/2R I2=I3=V/R – the same Series vs parallel - I Lecture X

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