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If we had a group of n resistors connected in a parallel combination, and one of the resistors burns out, what is the effective resistance? I had a question based on this in my exam recently and I want to make sure I was right. I assumed a resistor burning out would result in an open circuit.

Exam question

I assumed that a resistor results in an open circuit when it burns out.

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  • \$\begingroup\$ Does this answer your question? What happens to resistor when it “breaks” due to over-current or over voltage? \$\endgroup\$ Commented Dec 11, 2019 at 11:35
  • \$\begingroup\$ I can add the picture of my question paper , I'll edit the question, please give me a minute \$\endgroup\$ Commented Dec 11, 2019 at 12:06
  • \$\begingroup\$ Yes, resistors become open circuit when they burn out. \$\endgroup\$ Commented Dec 11, 2019 at 12:20
  • \$\begingroup\$ Hopefully they do not damage the circuit board or start a fire when burning out. Some are even rated for this ("flameproof") for safety. \$\endgroup\$
    – rdtsc
    Commented Dec 11, 2019 at 13:26
  • \$\begingroup\$ [My original comment used "n" but now that you've posted the question where n has a different meaning I have deleted the original and re-written it here.] By burning out you mean "has failed open-circuit"? Thought experiment: (1) What is the resistance of m identical resistors in parallel? (2) What is the resistance of m - 1 identical resistors in parallel? Higher or lower? (3) What then is the effect of that group on the whole circuit? \$\endgroup\$
    – Transistor
    Commented Dec 11, 2019 at 14:49

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When answering exam questions you unfortunately have to make assumptions. If no numbers are given then you generally are expected to assume an extreme case, the extreme cases would be open-circuit or short-circuit, the question makes no sense with the short-circuit assumption, so open-circuit it is.

Open-circuit is certainly one plausible outcome of a resistor "burning out", but I would not assume during actual circuit design that it was the only possibility.

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  • \$\begingroup\$ Thank you sir, that was exactly what I assumed. \$\endgroup\$ Commented Dec 11, 2019 at 15:52

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