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PHY 2049: Physics II

PHY 2049: Physics II. Tutoring Center is open in room NPB 1215, M-F 12:00AM -4:00PM. It is free. Homework set for Chapter 28 has been posted. Circuits, networks and all that. Spread of information By Foot Spread of Christianity, St. Paul and his travels Buddhist missionaries

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PHY 2049: Physics II

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  1. PHY 2049: Physics II • Tutoring Center is open in room NPB 1215, M-F 12:00AM -4:00PM. It is free. • Homework set for Chapter 28 has been posted.

  2. Circuits, networks and all that • Spread of information • By Foot • Spread of Christianity, St. Paul and his travels • Buddhist missionaries • By Electromagnetic waves. • Connections (degrees of) • Telegraph, Radio, TV, cell phones • By Internet • Connections

  3. hitt • A portion of a circuit is shown, with the values of the currents given for some branches. What is the direction and value of the current i? • A. ↓, 6A B. ↑, 6A C. ↓, 4A D. ↑, 4A E. ↓, 2A

  4. Electrical circuits • Branches and junctions • Kirchhoff's Rules • All current coming to a junction equals the total current leaving the junction. (charge conservation) • Around any closed loop, the total voltage drop vanishes. (work around a closed loop)

  5. Kirchhoff’s rules • Identify a branch, assign a current. All currents obey the junction rule. • Identify a loop, assign a direction: • A battery, V from – to + is >0 • A resistor R, along the current is V = -IR • Each loop gives an equation, solve for the unknowns

  6. Circuits, Junctions • Charge can not be created, nor destroyed • Total Current in = Total current out • i = 8A - i

  7. Loop calculations • R2 and R3 are parallel. • The net is in series

  8. Not so fast • 5 resistances and 3 batteries. Neither parallel nor in series. • 3 braches, 2 junctions and 3 loops. • i1 + i2 = i3 • E1 +i1R1-i2R2-E2+i1R1 = 0 • E1 + i1R1+i3R1-E2+i3R1+i1R1 = 0

  9. What is i? All V = 10 Volts and all R = 4 Ohms

  10. What is i? All V = 10 Volts and all R = 4 Ohms? What is j? What is k? j k

  11. What is i? All V = 10 Volts and all R = 4 Ohms j k

  12. R = 4Ω, V = 4 V, what is the current through R?

  13. R = 4Ω, V = 4 V, what is the current through R? 8 = 4I => I = 2A

  14. Figure shows five 5.00 Ω resistors. Find the equivalent resistance between points (a) F and H and (b) F and G. (Hint: For each pair of points, imagine that a battery is connected across the pair.)

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