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Thevenin’s, Norton’s, and Maximum Power Transfer Theorems
46 questions By Tony R. Kuphaldt
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Question 43 of 46
At what load resistance value is the power dissipation maximized for the source’s internal resistance?
Reveal answerSource dissipation will be maximized at Rload = 0 Ω. Surprised at this answer? Expecting power to be maximized at Rload = Rsource, perhaps? If so, you have misunderstood the Maximum Power Transfer Theorem.
Notes:The wrong answer anticipated in the “Answer” section reflects a common student misconception, and a tendency to memorize simple rules rather than think and analyze circuit behavior. Remind your students that the Maximum Power Transfer Theorem specifies what value the load resistance should be at to maximize power dissipation at that same load, not elsewhere.
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Question 44 of 46
Explain why it is important for optimum performance to connect speakers of the proper impedance to an audio power amplifier.
Reveal answerImproper speaker impedance may result in low power output (excessive Z) or overheating of the amplifier (insufficient Z).
Follow-up question: since consumer-grade audio speakers are typically uniform in impedance (8 Ω is a very popular value), how would it be possible to connect a wrong speaker impedance to an audio power amplifier?
Notes:I find it typical that students of electronics new to basic electrical theory are fascinated by discussions related to audio technology, as it is difficult to find someone who does not in some way appreciate music. This is a good thing, for the more “real” you can make your students’ classroom experience, the better they will learn.
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Question 45 of 46
At what source resistance value is the power dissipation maximized for the load?
Reveal answerSource dissipation will be maximized at Rsource = 0 Ω. Surprised at this answer? Expecting power to be maximized at Rsource = Rload, perhaps? If so, you have misunderstood the Maximum Power Transfer Theorem.
Notes:The wrong answer anticipated in the “Answer” section reflects a common student misconception, and a tendency to memorize simple rules rather than think and analyze circuit behavior. Remind your students that the Maximum Power Transfer Theorem specifies what value the load resistance should be at to maximize power dissipation at that same load, not elsewhere.
I think there is an error in 8th question, Thevenin’s resistance must be 479.53 and not 210.53
There is another mistake in question 39:
“this student’s power source circuit resembles a 3 volt source in series with a 5 kΩ resistance”—should be 2.5 kΩ resistance