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19 Current, Resistance, & DC Circuits

Explore the fundamental concepts of electric current, resistance, Ohm's Law, electromotive force, circuit configurations, power, and Kirchhoff's Rules. Learn how to measure current, voltage, and analyze circuits effectively.

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19 Current, Resistance, & DC Circuits

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  1. 19 Current, Resistance, & DC Circuits

  2. Electric Current Current: net charge passing through a cross-section per unit time. Units: Ampere (A), 1 A = 1C/s (mA, mA, nA, pA) Scalar , Positive current=flowing direction of positive charges

  3. Resistance and Ohm’s Law A L R: resistance, L: length, A:cross section, r: resistivity Unit(R): Ohm(W), 1W = 1V/A; Unit(r): ohm.meter (W.m) Temperature dependence: RT = R0[1+a(T-T0)] T in Celsius, R0 = R(T=T0=20oC) a: temperature coefficient (0.003~0.005 oC-1)

  4. Resistivities of Different Materials

  5. Superconductivity & Non-ohmic Conductors

  6. Electromotive Force & Circuits A pump is needed to keep the water circulating pump~electromotive force (emf) Circulating without pump No emf~imposiple

  7. emf Source (e) Terminal voltage: Vab = eVab = e = IR (ideal emf) Vab = e -Ir (with internal resistance, r)

  8. Voltage and Current Measurements

  9. Potential drops and rises in circuit

  10. Energy and Power in Electric Circuits Power: the energy consumed per unit time. Power Output of a Source Ir2 is the energy dissipated inside the sourceheat

  11. Resistors in Series & Parallel (in series) (in parallel)

  12. Combinations

  13. Kirchhoff’s Rules Junction Rule Loop Rule

  14. Kirchhoff’s Rules

  15. Electrical Measuring Instruments Ammeters Galvanometer Voltmeters

  16. Resistance-Capacitance Circuits and Transient Effects

  17. Summary: Current

  18. Summary: Resistance & Ohm’s Law

  19. Summary: emf

  20. Summary: Energy & Power

  21. Summary: Resistors in Parallel & Series (in series) (in parallel)

  22. Summary: Kirchhoff’s Rules

  23. Summary: Charging & Discharging

  24. Homework

  25. Problem 57

  26. Problem 61

  27. Problem 52 & 53

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