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Quiz Preparation

Quiz Preparation. Have Quiz sheet ready. Top Center : QUIZ 3 Upper Right: Name (L, F, MI), Today’s date 9/4/12 Lab day , time section number. Announcements. Read Chapter 6 before lab. Work problems at the end of the Chapter 6 for practice. Solutions on web site.

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Quiz Preparation

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  1. Quiz Preparation • Have Quiz sheet ready. • Top Center:QUIZ 3 • Upper Right: • Name (L, F, MI), • Today’s date 9/4/12 • Lab day , time • section number

  2. Announcements • Read Chapter 6 before lab. • Work problems at the end of the Chapter 6 for practice. Solutions on web site. • Be sure to do the Pre-Lab assignment. You will lose in-lab points if you do not have the pre-lab worked when you arrive at lab.

  3. Electricity – Water Analogy • Electricity flows through a circuit like water through a pipe. • charge -- # of water molecules in the pipe • current -- water flow rate (gallons per minute) • voltage – pressure (psi = pounds per square inch) • resistance -- resistance to flow (inverse of pipe cross-sectional area) • capacitance -- water stored under pressure (e.g. a bladder tank)

  4. Units • charge -- coulombs (C) • current -- amperes (A), A=C/s • voltage -- volts (V) • resistance -- ohms (),  =V/A • capacitance -- farads (F), F = C/V Note: Farads are huge units -- usually use F (microfarads)

  5. Circuit Elements • voltage source (e.g. battery) – like water pump with specified pressure. Units: volts (V)

  6. Circuit Elements • resistor -- pipe with small cross-sectional area that impedes water flow. Units: ohms () Wire can be viewed as a resistor with very low or zero resistance.

  7. Circuit Elements • CAPACITOR – a reservoir or sponge that can store water (charge). Units of capacitance: Farads (F)

  8. Circuit Elements • diode -- valve that only allows current flow one direction. (No units) current

  9. Quiz • 1. Electric current is analogous to: • a. water pressure • b. water flow rate • c. # of water molecules in the pipe • 2. Voltage is analogous to: • a. water pressure • b. water flow rate • c. # of water molecules in the pipe

  10. Ohm’s Law • The current I flowing through a resistor is proportional to the voltage V across it and inversely proportional to the resistance R: or

  11. I + 5V - 100  I = 5/100 = 0.05A Ohm’s Law - Example Always: • Label current directions • Put +/- signs on voltages Passive sign convention: place the positive voltage reference at the same terminal that the current enters

  12. I + 10V - 1000  Quiz 3. The current I is (a) 100 A (b) 0.01 A (c) -10,000 A

  13. Connection Types • Series (daisy chain) • Parallel (side by side)

  14. I Series Connection • Single branch. Current is the same through all elements.

  15. Series Connection • Resistors add in series. Ex: R1=50, R2=100   R=150 

  16. Multiple voltage sources in series add. These circuits are equivalent. Multiple Voltage Sources

  17. Wait – I thought they ADDED! • 10 + 4 = 6? • Have to look at the polarity + 10 - 1k - 4 +

  18. Parallel Connection • Multiple branches connected at both ends. The voltage is the same across all elements.

  19. Parallel Connection • The reciprocal of resistance adds. For two resistors only = product / sum Ex: R1=50, R2=100   R=(50)(100)/150=33.33 

  20. Series vs. Parallel Are the lights in your house/apartment wired in series or parallel? Answer: Parallel!

  21. Voltage Division (wire) (motor) • If R1 represents the wire resistance and R2 represents the motor and motor circuit resistance, we want R1 to be as small as possible. This will deliver the maximum voltage to the motor.

  22. Voltage Division - Example 10 15V 20

  23. Resistors in Parallel - Example • What is the current in each branch? I1 I2 Vo

  24. Resistors in Parallel - Example • Voltage is the same across each branch– use Ohm’s law: I1 I2 Vo

  25. Resistors in Parallel - Example • Ohm’s law I1 I2 Vo 15V 20 10

  26. Series/Parallel Example • What is the current in each branch? I1 I2

  27. Series/Parallel Example • Combine the two 1kΩ resistors in series. I1 I2 2k

  28. Diode Example + VR - • What is the current in the circuit (I) and the voltage drop across the resistor (VR)? I R Vo

  29. Diode Example + VR - I R VD=0.7V Vo

  30. Diode Example + VR - I 1k VD=0.7V 9V

  31. Breadboards • Used for rapid prototyping • Easier & faster than soldering • Allow for easy alterations • Generally for temporary use • Components just plug in

  32. How a Breadboard Works • Connect components by plugging them in • Components are connected by copper wires underneath holes

  33. Connecting Resistors in Series

  34. Connecting Resistors in Parallel

  35. Quiz 4. Voltage division is used (a) to find the voltage across a single element in a series circuit (b) to find the voltage across a single branch in a parallel circuit (c) to determine the fair allocation of batteries in a team-based design

  36. Quiz 5. Current division is used (a) to find the current through a single element in a series circuit (b) to find the current through a single branch in a parallel circuit (c) to determine the fair allocation of batteries in a team-based design

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