Combination circuit help

[ggunn]

My point is, from the forum point of view the circuit is to be analyzed from all angles and not merely to help the OP to gain more marks from the exam without understanding the theory behind.

In order to that you must be shown the entire circuit; in the original problem as stated this is not explicitly the case. If you assume that the entire 50V drop is exhibited across the three resistor network, you are, as Perry Mason would say, assuming facts not in evidence. That's incompetent, irrelevant, and immaterial.

 

[Sahib]

In order to that you must be shown the entire circuit; in the original problem as stated this is not explicitly the case. If you assume that the entire 50V drop is exhibited across the three resistor network, you are, as Perry Mason would say, assuming facts not in evidence. That's incompetent, irrelevant, and immaterial.

It is ridiculous to fail to notice these words in the problem statement:''.....the combination in a 50 volt circuit.'' and to think that the entire 50V drop is not exhibited across the three resistor network.

 

[Besoeker]

It is ridiculous to fail to notice these words in the problem statement:''.....the combination in a 50 volt circuit.'' and to think that the entire 50V drop is not exhibited across the three resistor network.

The information given does not support the assumption that the entire 50V is supported across the three resistor network.

 

[Sahib]

The information given does not support the assumption that the entire 50V is supported across the three resistor network.

What would happen if the current value through 242ohm resistance not given in the problem? Would you then proceed to find the current value through 180 0hm resistance using 50V source voltage assumption or declare the problem insoluble?
Ridiculous.

 

[mivey]

The real test posed by this question is to see if the testee can separate the information needed to solve the problem from extraneous irrelevant (and misleading) data. The calculation is trivial by comparison.

I agree. I have seen that many times.

 

[mivey]

What would happen if the current value through 242ohm resistance not given in the problem? Would you then proceed to find the current value through 180 0hm resistance using 50V source voltage assumption or declare the problem insoluble?
Ridiculous.

Are you really asking what if the problem were a different problem? Why would you want to make that ridiculous extrapolation?

Leave the making of mountains out of molehills to a more technically challenging thread then we can cast looks of distain (do we have a distain emoticon?) at the ECs who think we are making mountains out of molehills. As for this thread, where's the joy?

 

[Sahib]

Are you really asking what if the problem were a different problem? Why would you want to make that ridiculous extrapolation?

No, I just wanted to shed some light that the value 50V is not an ASSUMPTION but a value given in the problem.

As for this thread, where's the joy?

I am sorry if I made it a serious discussion.

 

[mivey]

No, I just wanted to shed some light that the value 50V is not an ASSUMPTION but a value given in the problem.

And it was, as has been pointed out, purposeful unneeded information used to weed out the pretenders.

I am sorry if I made it a serious discussion.

No problem. Just seemed like a pretty cut-and-dried problem. I was thinking too much digging away at endless possibilities on a simple circuit for a person of your knowledge but if you feel froggy...

 

[kwired]

No, I just wanted to shed some light that the value 50V is not an ASSUMPTION but a value given in the problem.

It could have been worded a little better to make it clear that it is the source voltage. Most have assumed it is, but some could assume it is voltage across some other part of the circuit.

 

[ggunn]

No, I just wanted to shed some light that the value 50V is not an ASSUMPTION but a value given in the problem.

I am sorry if I made it a serious discussion.

It is absolutely an assumption on your part. Show me where it explicitly says that there is 50V across the resistor network. You can't; it's not in there. The network is in a 50V circuit, but it's not necessarily the entire 50V circuit. Furthermore, if you do an analysis of the given facts, it cannot be the entire 50V circuit.

Perhaps you haven't taken any/many timed multiple choice exams; this is a very common practice. The problem statement contains language intentionally designed to mislead the testee if he makes assumptions that are not explicitly in the problem statement. The road signs are there and obvious to anyone paying attention; if you assume that there is 50V across the network, the (explicitly) stated current through that resistor cannot be correct. When faced with an apparent contradiction, you go with what is explicitly stated. Is it trickery? You betcha; it's designed to reward critical thinking. He who sees through the trick gets the question scored "correct". If it makes the testee take time to fully analyze it rather going straight to the crux of the biscuit (the current through one parallel resistor unambiguously defines the current through the other irrespective of what is going on in the rest of the circuit), he is penalized even if he eventually gets the right answer because it's a timed exam.

This really is pretty standard stuff.

 

[gar]

130726-0933 EDT

Some have proposed that in a real world problem there will be extraneous information, and that it is appropriate for tests to be written with that type of presentation. That is a useful approach, but the real world won't be inconsistent. In the real world you may have instrumentation error problems, or wrong information.

This problem is inconsistent when some improper assumptions are made, namely that the 50 V is applied across the three resistor network, and the answer list was wrong for any correct reasoning about the circuit.

hurk27 showed how incorrect reasoning of the problem could produce one of the given answers. The author of the original question did not understand electrical circuit theory, or was sloppy in creating the question. No double checking. Using the erroneous method that hurk27 found, the calculated value is 0.073562, and when rounded is 73.6 which is exactly one of the wrong answers. Not just something close.

.

 

[kwired]

130726-0933 EDT

Some have proposed that in a real world problem there will be extraneous information, and that it is appropriate for tests to be written with that type of presentation. That is a useful approach, but the real world won't be inconsistent. In the real world you may have instrumentation error problems, or wrong information.

This problem is inconsistent when some improper assumptions are made, namely that the 50 V is applied across the three resistor network, and the answer list was wrong for any correct reasoning about the circuit.

hurk27 showed how incorrect reasoning of the problem could produce one of the given answers. The author of the original question did not understand electrical circuit theory, or was sloppy in creating the question. No double checking. Using the erroneous method that hurk27 found, the calculated value is 0.073562, and when rounded is 73.6 which is exactly one of the wrong answers. Not just something close.

.

Possible that the method hurk discovered was exactly what the writer of the question did to come up with the final written result.

Writer may be well competent in this area and simply made a mistake this time, after all he is likely human.

 

[ggunn]

Possible that the method hurk discovered was exactly what the writer of the question did to come up with the final written result.

Writer may be well competent in this area and simply made a mistake this time, after all he is likely human.

The trickster tricked his own self, it appears. Hoist with his own petard, as it were.

 

[Besoeker]

I am sorry if I made it a serious discussion.

You didn't.

 

[Besoeker]

As my late, great friend Tommy use to say:
"The man who never made a mistake never made anything."

 

[kwired]

As my late, great friend Tommy use to say:
"The man who never made a mistake never made anything."

My high school math teacher always said "I never make mistakes. I once thought I made a mistake, but I was wrong".

 

[Sahib]

You didn't.

Then the question posed in post #64 would be easy to answer.

 

[mivey]

130726-0933 EDT

Some have proposed that in a real world problem there will be extraneous information, and that it is appropriate for tests to be written with that type of presentation. That is a useful approach, but the real world won't be inconsistent. In the real world you may have instrumentation error problems, or wrong information.

This problem is inconsistent when some improper assumptions are made, namely that the 50 V is applied across the three resistor network, and the answer list was wrong for any correct reasoning about the circuit.

hurk27 showed how incorrect reasoning of the problem could produce one of the given answers. The author of the original question did not understand electrical circuit theory, or was sloppy in creating the question. No double checking. Using the erroneous method that hurk27 found, the calculated value is 0.073562, and when rounded is 73.6 which is exactly one of the wrong answers. Not just something close.

.

You & hurk27 did make it interesting in trying to find how the question and answers came to be but in this case, I would write down the answer and note the provided answers were not valid solutions.

 

[mivey]

Writer may be well competent in this area and simply made a mistake this time, after all he is likely human.

I suspect the writer is competent and that it could be a publishing error. If the writer updated the material it is highly possible that the change was made incorrectly. Happens all the time, even after the author notifies the publisher more than once. Maybe they did not update the answers along with the question.

 

[ggunn]

You & hurk27 did make it interesting in trying to find how the question and answers came to be but in this case, I would write down the answer and note the provided answers were not valid solutions.

Unfortunately, most exams like this are electronically graded and your written in answer would not be logged. But at least it wouldn't be counted wrong; usually in order to discourage blind guessing there is more of a penalty for answering incorrectly than for not answering at all. The scoring I have often seen is R - W/4 for exams with five choice questions. That way if you don't answer a single question or if you guess randomly on each one, you get a zero score either way.