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Lecture 2

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Lecture 2. 2.1 Sources 2.2 Ohm’s Law 2.4 Kirchhoff’s Laws. Voltage and Current Sources. Independent Sources. Characteristics. An independent source establishes a voltage or current in a circuit without relying on voltages and currents elsewhere in the circuit.

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Lecture 2

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  1. Lecture 2

    2.1 Sources 2.2 Ohm’s Law 2.4 Kirchhoff’s Laws
  2. Voltage and Current Sources
  3. Independent Sources
  4. Characteristics An independent source establishes a voltage or current in a circuit without relying on voltages and currents elsewhere in the circuit. The value of the voltage or current supplied is specified by the value of the independent source alone.
  5. Exercise
  6. Electrochemistry of a Lemon Battery - e- + Add standard reduction potential to obtain the voltage across the terminals. Zn→Zn2++2e- +0.76 V +0.34 V Cu2++2e-→Cu Net: 1.10 V
  7. Typical Values 1 Lemon 0.9 Volts 300 uA 270 uW Red LED: 1.7 V 500 uA 850 uW, i.e. 3 lemons in series
  8. Ohm’s Law
  9. Analogy The height of the water=voltage The volume of flow through the hole per second=current The smallness of the hole = resistance Water wheel hit by the flow from the hole = power
  10. Thought Experiment #1 Fixed hole dimension↔ Fixed R Height of water↑ → flow rate↑. V↑ → I↑
  11. Thought Experiment #2 Fixed height of water↔ Fixed V Hole dimension↑ → flow rate↑ R↓ → I↑
  12. Derivation of Ohm’s Law Three variables: V,I and R. Different Possibilities: V=IR (1) I=VR (2) R=VI (3) Intuition If R is constant, V↑ → I↑. (3) is not possible. (1) and (2) are possible. If V is constant, R↓ → I↑. (2) and (3) are not possible
  13. Ohm’s Law V=IR Mnemonic: Victory Is Rare V represents the voltage difference between the two terminals of a resistor!
  14. Exercise Calculate the value va Determine the power dissipated in the resistor
  15. Exercise ` Current is equal to 50V/25 Ohms=2A The battery provides -100W of power. The resistor uses +100 W of power.
  16. My Favorite Quiz Question What is the current through the 25 Ohm resistor? Current =(50V-25V)/25 Ohms=1A
  17. Current Flows from a point of High potential to a point of Low potential
  18. Problem 2.21 Label the (+) and (-) terminal of the 65 Ω s and 50 Ω given the assumed direction of i0 and i1.
  19. Kirchhoff’s Laws
  20. KCL Kirchhoff’s Current law (KCL) The algebraic sum of all the currents at any node in a circuit equals zero
  21. Bipolar Junction Transistor Example Bipolar Junction Transistor IE=IB+IC Electronics I (ES230)
  22. A Voltage Adder Using an Operational Amplifier IR1 IRF IR2 KCL: IR1+IR2=IRF (Application:Noise Cancellation) Class: ES220
  23. KVL Kirchhoff’s Voltage Law The algebraic sum of all the voltage around any closed path in a circuit equals zero
  24. Exercise Sum the voltages around each designated path in the circuit
  25. Example 2.8 KCL at b KVL around cabc loop Solve for io and i1
  26. Problem 2.18 KCL at the top node KVL around the right loop Find i1, i2, vo
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