Friends  I am, fairly late in life, trying to learn electronics in my spare time using a highschool/college textbook ('Electronics Fundamentals' by Floyd). I'm about 200 pages in, at this point. I'm working on parallelresistance networks and ran into this problem:
A certain parallel network consists of five 1/2Watt resistors with the following values: 1.8kΩ, 2.2kΩ, 3.3kΩ, 3.9kΩ and 4.7kΩ. As you slowly increase the voltage across the parallel circuit the current slowly increases. Suddenly the current drops to a lower value.
a) Excluding power supply failure, what happened?
b) What is the maximum voltage you should have supplied?
c) Specifically, what should be done to repair the circuit?
Of course, a resistor has failed. In deriving the maximum voltage, I reasoned that the maximum power for this circuit would be 2.5W as power is additive in parallel circuits.
I calculated a total resistance for the network of 561Ω.
I used what I could recall of my college algebra to manipulate the formula:
P=IV into V=√PR
and then used that to calculate the maximum voltage as 37.45v. The book's answer, though, is 30v. They do not show the steps; only the result.
I am the sort of person who finds it difficult to let go of an unsolved problem. In this case, I don't know if my approach is wrong, if my algebra is faulty or if the book is incorrect. If someone could set me on the right track, I'd be grateful. Thank you for the time and energy spent on such an elementary problem.
A certain parallel network consists of five 1/2Watt resistors with the following values: 1.8kΩ, 2.2kΩ, 3.3kΩ, 3.9kΩ and 4.7kΩ. As you slowly increase the voltage across the parallel circuit the current slowly increases. Suddenly the current drops to a lower value.
a) Excluding power supply failure, what happened?
b) What is the maximum voltage you should have supplied?
c) Specifically, what should be done to repair the circuit?
Of course, a resistor has failed. In deriving the maximum voltage, I reasoned that the maximum power for this circuit would be 2.5W as power is additive in parallel circuits.
I calculated a total resistance for the network of 561Ω.
I used what I could recall of my college algebra to manipulate the formula:
P=IV into V=√PR
and then used that to calculate the maximum voltage as 37.45v. The book's answer, though, is 30v. They do not show the steps; only the result.
I am the sort of person who finds it difficult to let go of an unsolved problem. In this case, I don't know if my approach is wrong, if my algebra is faulty or if the book is incorrect. If someone could set me on the right track, I'd be grateful. Thank you for the time and energy spent on such an elementary problem.
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