e17lecture2

e17lecture2 - Ch. 2: Circuit Elements Voltage and current...

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1 Ch. 2: Circuit Elements Voltage and current sources Electrical resistance (Ohm’s Law) Constructing a circuit model Kirchhoff’s Laws Analysis of a circuit containing dependent sources Electrical Sources An “electrical source” converts nonelectrical energy to electrical energy or vice versa (e.g., a generator, a motor). Key point: An electrical source either delivers or absorbs electric power, while generally maintaining either a constant voltage or current. Ideal Sources Ideal voltage source: maintains a prescribed voltage across two terminals, regardless of the current through it. This means that given the voltage, the current cannot be determined. Ideal current source: maintains a prescribed current through two terminals, regardless of the voltage across the terminals. This means that given the current, the voltage cannot be determined. Ideal Voltage Source Ideal Current Source Independent vs. Dependent Sources Independent source: establishes a voltage or current in a circuit without relying on voltages or currents elsewhere in the circuit. Symbol for independent source = circle (e.g., previous slide). Dependent source: establishes a voltage or current that depends on a voltage or current elsewhere. Symbol for dependent source = diamond (next slide). Dependent Sources
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2 Active vs. Passive Elements Active circuit elements generate electrical energy. Examples: the voltage and current sources on previous slides. Passive circuit elements don’t generate energy. Examples: resistors, capacitors, inductors. Example 2.1: Which of the interconnections in (a)-(e) are valid? Example 2.1: Which of the interconnections in (a)-(e) are valid? Answers: (a) is valid (b) is valid (c) is not valid (d) is not valid (e) is valid Example 2.2: Which interconnections in (a) through (d) are valid? Answer: Example 2.2: Which interconnections in (a) through (d) are valid? Answer: (a) no, (b) yes, (c) yes, (d) no Assessment 2.1 (a) What value of v_g below is required in order for the interconnection to be valid? Answer: (b) For this value of v_g, find the power associated with the 8 A source. Answer:
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3 Assessment 2.1 (a) What value of v_g below is required in order for the interconnection to be valid? Answer: i_b = -8, so i_b/4 = -2 and v_g = -2. (b) For this value of v_g, find the power associated with the 8 A source. Answer: Assessment 2.1 (a) What value of v_g below is required in order for the interconnection to be valid? Answer: i_b = -8, so i_b/4 = -2 and v_g = -2. (b) For this value of v_g, find the power associated with the 8 A source. Answer: p = vi = (-2)(8) = -16 W (16 W extracted from the 8 A source and delivered to the circuit) + - Assessment 2.2 (a) What value of is required in order for the interconnection to be valid? Answer:
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e17lecture2 - Ch. 2: Circuit Elements Voltage and current...

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