Lecture 2 2.1 Sources 2.2 Ohm’s Law 2.4 Kirchhoff’s Laws.
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Transcript of Lecture 2 2.1 Sources 2.2 Ohm’s Law 2.4 Kirchhoff’s Laws.
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Lecture 2
2.1 Sources2.2 Ohm’s Law
2.4 Kirchhoff’s Laws
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Voltage and Current Sources
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Independent Sources
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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.
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Exercise
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Dependent Sources
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Characteristics
• Dependent sources establish a voltage or current whose value depends on the value of a voltage or current else where in the circuit.
• You cannot specify the value of a dependent source unless you know the value of the voltage or current on which it depends.
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Exercise
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Exercise
What value of Vg is required for the wiring to be valid?
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Ohm’s Law
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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
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Thought Experiment #1
Fixed hole dimension↔ Fixed RHeight of water↑ → flow rate↑.V↑ → I↑
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Thought Experiment #2
Fixed height of water↔ Fixed VHole dimension↑ → flow rate↑R↓ → I↑
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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
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Ohm’s Law
• V=IR• Mnemonic: Victory Is Rare
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Exercise
• Calculate the value va• Determine the power dissipated in the resistor
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Exercise
Calculate id
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Kirchhoff’s Laws
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KCL
• Kirchhoff’s Current law (KCL)–The algebraic sum of all the currents at
any node in a circuit equals zero
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Exercise
Sum the currents at each node
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Multisim Demo
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KVL
• Kirchhoff’s Voltage Law–The algebraic sum of all the voltage
around any closed path in a circuit equals zero
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Exercise
Sum the voltages around each designated path in the circuit
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Example 2.8
1.KCL at b2.KVL around cabc loop3.Solve for io and i1
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Problem 2.18
1.KCL at the top node2.KVL around the right loop3.Find i1, i2, vo
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Problem 2.21
Find i1 if i0 is 1A.