Calculation

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gar said:
230103-1003 EST

ggunn:

Where in the original post was there any mention of "power" being held constant? What is held constant is the total line to line voltage.

And by implication, since tungsten filament bulbs are the load, the relative bulb resistances are very different between each other when the center wire is open vs closed.
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Where did the OP state the 'lamps' were tungsten?

Where in the OP did it say the problem should be solved over a time range rather than at a singe point in time after the system has stabilized?
 
Besoeker3 said:
Oh chill ! I don't hate anything and I very much enjoy this forum. The concept you are promoting is correct. But the mathematics is wrong. The tutor should have known that and should have sorted that.
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I think someone studying to be an engineer likely learns some the finer details that aren't as important to the lesson in the OP at a sooner time than maybe a typical field electrician would. There probably is some out there that been electricians for several years and don't know some those finer details, and for the most part haven't needed to know them very often. Guys that do a lot of troubleshooting will pick up on it at some point. Guys that install things but seldom do any troubleshooting may never really know it.

Kind of no different than a first or second year electrician that can bend conduit quicker and more accurately than an engineer can. The engineer possibly can do it but normally doesn't need to know all the little tricks that someone that does it all the time does
 
gar said:
230103-1003 EST

ggunn:

Where in the original post was there any mention of "power" being held constant? What is held constant is the total line to line voltage
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The question as stated declares that the light bulbs are of specific Watt ratings, and those power numbers are used in the calculations. At least that is how I remember it but there has been a whole lot of smoke blown since then. :D
 
ActionDave said:
No. A light bulb is a tangible
and relatable item to introduce a concept.
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Indeed it is. But the voltage between the two bulbs does not equate to their ratios. The students might not understand that but the tutor have known the difference that bulbs would react differently as their temperature changes. I'm sure you know that.
 
Clearly the test question could be improved by simply adding to the text "Treat the lamps as fixed resistors," or maybe "Assume the lamps obey Ohm's Law." I'll let the rest of you argue about the magnitude of the deficiency of that omission. Although for all we know the question may be from a class in which it was already established that for all purposes that would be the case, just like we assume the transformer is ideal, etc.

Cheers, Wayne
 
wwhitney said:
Although for all we know the question may be from a class in which it was already established that for all purposes that would be the case, just like we assume the transformer is ideal, etc.
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Which is a very common practice.
I have had many courses where we were not to assume any non-ideal condition not explicitly presented in the test, and I have had tests where we were supposed to make and document conditions which we would expect in the real world.
 
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