Author Topic: Trying to prove a point  (Read 5502 times)

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Offline brabus

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Re: Trying to prove a point
« Reply #25 on: June 07, 2019, 09:11:08 am »
The correct answer is D.

No relay is mentioned, so a "switch" can be any manually activated switch, or a relay as well. The question only says "electrical state of the switch contacts".

Your teacher is very likely aware that the question is badly formulated, and that D is the correct answer, but he must defend his role as an educator*. What would happen if he accepted your point, even if it's correct? He should revise all the tests and reformulate the scores, surely facing hundreds of students who want to keep their marks.
It is a lot easier for him to just state his point, without giving you a clear explanation whatsoever.

You, as a student and a growing man, are learning a lot more from this experience than just the definition of a bloody switch.

*Otherwise, as often happens, he is just a poor chap that randomly snake his way into education, with no interest at all in sustaining a conflict of ideas with a student - we all know that kind of guy.


What I would do:
- Avoid conflict, of course.
- Buy a NC push button, bring it to class, and ask your teacher, following the answer C, how the NO/NC status of the switch is anyhow influenced by the power applied (to what?).
 

Offline DDunfield

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Re: Trying to prove a point
« Reply #26 on: June 07, 2019, 09:21:00 am »
No, a switch can be actuated by other means. For example end position/calibration switch in a machine, alarm system reed switch and power button of a notebook. Each one is a NO or NC switch.

Three examples of momentary switches which must be held in the activated state, either by a moving part of a machine, presence of a magnet in close proximity or by a notebook cover pressing on it's little "stub". These switches will resume their "normal" state when the source of activation is removed.

The "normal" state has nothing to do with whether or not the switch is held active more or less than it is held inactive, it is the state the switch assumes when there is no activating force applied to it. which is why the terms don't really apply to switches which naturally have more than one steady state.

When you spec. a toggle switch, you don't care about N.O. or N.C. because the switch can be used either way (unless it happens to have ON/OFF markings on it and you want them to match the logical function of your device). For a momentary switch the distinction becomes important as you must decide which states represents "activated" and "deactivated".

Dave

 

Offline DDunfield

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Re: Trying to prove a point
« Reply #27 on: June 07, 2019, 09:25:34 am »
- Buy a NC push button, bring it to class, and ask your teacher, following the answer C, how the NO/NC status of the switch is anyhow influenced by the power applied (to what?).

You should make it one with visible contacts, otherwise you can't observe it's state without applying power  ;D

Dave

Yeah - I know the pic is a N.O. button, but you get the idea.
« Last Edit: June 07, 2019, 09:58:50 am by DDunfield »
 

Offline DimitriP

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Re: Trying to prove a point
« Reply #28 on: June 07, 2019, 09:45:35 am »
Does a device have an electrical state when power is not applied?
Doesn't an "electrical state" imply existence of ....electricity?

Or to put in in other words, what's the weight of an elephant with no gravity "applied"?
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Offline DDunfield

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Re: Trying to prove a point
« Reply #29 on: June 07, 2019, 10:15:59 am »
Does a device have an electrical state when power is not applied?
Doesn't an "electrical state" imply existence of ....electricity?

Yep - I interchanged A and C when I referred back to the questions, probably because that was the only way the teachers answer could make any sense. "Power not applied" makes no sense at all, especially if you try to justify it with "electrical state".

Quote
Or to put in in other words, what's the weight of an elephant with no gravity "applied"?

That's an easy one: 0
The mass however remains the same.

Dave
 

Offline Brutte

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Re: Trying to prove a point
« Reply #30 on: June 07, 2019, 11:08:36 am »
The switch stays NO "normally open" no matter if you actuate it or not. It is a property of a switch and not its (electrical) state. So if you actuate a NO switch, the switch is still "normally open", although the switch starts conducting.
 

Offline Mechatrommer

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Re: Trying to prove a point
« Reply #31 on: June 07, 2019, 11:59:12 am »
No relay is mentioned, so a "switch" can be any manually activated switch, or a relay as well. The question only says "electrical state of the switch contacts".
manually actuated switches such as toggle switches, DPDT SPDT etc dont usually specified as NO nor NC. non-latched or returning switches are seldomly in use. so anyway, there are many type of switches, the person who made this question should take this into consideration. C is possible as well as D. the OP should also ask the teacher why it cant be D to understand his rational.
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Offline Rerouter

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Re: Trying to prove a point
« Reply #32 on: June 07, 2019, 12:17:04 pm »
When ever I feel like a question is ambiguous I just write my assumptions next to the answer,

Another Agreeing with D as the most correct answer given the assumptions, for the next one, a solar panel would be the most correct, as its the device generally used for that purpose. e.g. the lay person answer.

Back when I was studying electricity in TAFE, There where a few tests where the teacher had obviously had his own go at rewording or answer flipping the reference test to try and catch people who found a copy of the previous years one, sadly he introduced a ton of typos and made some things really hard to answer,

I did win him over to revising the next years test with my suggestions, but that was more or less earned respect, as I tried to not be a dick about it, and he knew I was smart on the topic,

Best memory of that class was creating a washing machine ladder-logic solution, I solved it in about 4 minutes, had 30 minutes to do it, so iterated it down to the least relays and function blocks possible, It for one flagged any other student that had (tried to) copied me, and left the teacher needing to simulate the thing to make sure it worked as he could not follow it. was a fun task,
 

Offline LateLesley

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Re: Trying to prove a point
« Reply #33 on: June 07, 2019, 06:35:15 pm »
Another vote for D.

They label the "Normal" positions when the switch isn't activated. So NC will connect to common (C) , and NO will be floating. Once the switch is operated, the NC is disconnected, and NO is connected to common.

Look at page 2 of this datasheet. http://www.farnell.com/datasheets/1702886.pdf

EDIT : And as applies to Relays- https://circuitdigest.com/article/relay-working-types-operation-applications

2nd EDIT : "In schematics switches are always drawn in the OFF position." http://www.zen22142.zen.co.uk/Prac/relay.htm
« Last Edit: June 07, 2019, 06:52:07 pm by LateLesley »
 

Offline Nominal Animal

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Re: Trying to prove a point
« Reply #34 on: June 07, 2019, 08:05:48 pm »
CoopedUp: If I were you, I'd find a SPDT switch with NO and NC markings (any common microswitch, or say a wall-mounted light switch), and show it to the teacher:


These markings only make sense on an electrical switch when NO and NC represent the state when the switch is not actuated.  Whether there is current flowing/power applied or not, has nothing to do with the switch (unless the power is enough to break the switch); the switch controls the electrical connection. Thus, D is the correct answer.

Someone mentioned relays; they too have NO and NC markings:

However, for a relay, "actuated" state == "energized" state == "when power is applied" to the relay coil; and "normal" state is when there is no power applied to the relay coil.

Whether there is current flowing over the NO/NC pins or not, is irrelevant.  So, D is definitely still correct; C (power is not applied) is only correct if we amend the "when power is not applied" with "to the relay coil".  Otherwise there is ambiguity in where power is applied with respect to the relay.

In every single case, whether power is conducted through the connection controlled by the switch or relay, is completely irrelevant.

My instincts say that your teacher is in error, because they are fixated on looking at things from the point of view of controlling the current/power, instead of controlling the electrical connection.  If I were you, I'd start my objection with something like "that might make sense if you looked at from the point of view of controlling the current/power, but in reality, a switch controls the electrical connection, and not the current or power conducted through the connection", followed by the images and text above.



We need to learn how correct the utterance or writing, instead of the person making it, because you are at a common task, not adversaries.

This sounds silly social games, but it is important nevertheless.  It means you acknowledge that perhaps the person isn't wrong, and is simply expressing themselves poorly.  It means that you do not question their knowledge, simply the way they express it.  Mis-expressing stuff is, in my experience, much more common than being straight-out wrong, at least when talking with professionals.

That approach to error-correcting is fortunately very contagious, and rapidly spreads: we feel better when our output is criticized and made better, without criticising us ourselves as a person.  It also helps the lecturer, as correcting errors have much less impact on ones self-esteem, as it is questioning the way things are put, rather than the knowledge it stems from.  I've been on both sides (student and lecturer), and it definitely works well for me.

This is also why I use a pseudonym on the intertubes: it reminds me that any and all criticism is based on my work product, and has nothing to do with me as a person, as none who use that pseudonym know me socially.  (As a self-broken husk of a man, I need that sort of a social crutch.)
 

Offline Brumby

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Re: Trying to prove a point
« Reply #35 on: June 08, 2019, 02:27:54 am »
From the outset, I've dismissed any answers where "power" is mentioned as a condition.  As a couple of others have said, the state of the switch contacts in their "normal" position is not defined by whether power is, or is not, applied.  It is defined by a physical property when examined in isolation.

The answer is D - but if the teacher has a different one in mind, I'd like to hear their reasoning.
 

Offline vk6zgo

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Re: Trying to prove a point
« Reply #36 on: June 08, 2019, 05:25:01 am »
NO & NC are by convention, in the unoperated state of the device, & do not depend upon the external circuit.
The other interpretations are misunderstanding at best, & sophistry at worst.
 

Offline StillTrying

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Re: Trying to prove a point
« Reply #37 on: June 08, 2019, 06:02:40 am »
"The abbreviations NO (normally open) and NC (normally closed) represent the electrical state of switch contacts when
C. power is not applied."

That makes no sense, is 100% wrong, ambiguous, and stupid, if they meant relay they should have said relay and not switch, and even then it should say coil somewhere. The OP should buy the teacher a hat with the correct answer on it.

Just a picture of one of those micro switches above with C, N/O, N/C on it would do. The explanation of where power comes in to it won't make any sense, so keep his new hat ready. :)
« Last Edit: June 08, 2019, 01:56:58 pm by StillTrying »
.  That took much longer than I thought it would.
 
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Online tautech

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Re: Trying to prove a point
« Reply #38 on: June 08, 2019, 07:54:49 am »
C. power is not applied.
Is 100% wrong, ambiguous, and stupid, if they meant relay they should have said relay and not switch, the OP should buy the teacher a hat with the correct answer on it.
This^^^
Teachers like to think they know everything and therefore occasionally need to be reset to show they are not infallible and in fact human and mistake prone like anyone else !
These are good examples of poor teaching skills and appropriate to take to the head of department for their correction of the syllabus.
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Offline Mechatrommer

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Re: Trying to prove a point
« Reply #39 on: June 08, 2019, 09:48:11 am »
C. power is not applied.
Is 100% wrong, ambiguous, and stupid, if they meant relay they should have said relay and not switch, the OP should buy the teacher a hat with the correct answer on it.
This^^^
Teachers like to think they know everything and therefore occasionally need to be reset to show they are not infallible and in fact human and mistake prone like anyone else !
These are good examples of poor teaching skills and appropriate to take to the head of department for their correction of the syllabus.
teaching skill is different from making question skill. syllabus is another thing made by another body. good teacher will encourage students to learn and accepts mistake incase student or anybody else highlight it. its more personal matter. i was lucky to get into some program to allow "non-education specialized course graduate" to enter education sector. i saw many of these "education specialized course" young teachers lack practical implementation of the syllabus they taught. but many from them are quite tolerant. stubborn teacher is quite rare though, its something they are taught in college? or just personal matter i dont know, but i believe its personal matter. i wish from time to time they will allow again "non-education specialized" such as from engineering, doctor, accountant degree course to become teacher so various discipline can share thoughts for better education.

if they meant relay they should have said relay and not switch, the OP should buy the teacher a hat with the correct answer on it.
so it mustn't be a transistor? he should call it an "electromagnetic coil actuated switch" not a relay, because relay means...
https://dictionary.cambridge.org/dictionary/english/relay
you cant apply power to nor "actuate" a group of people, its illegal.. well literalism hat off...
« Last Edit: June 08, 2019, 10:47:30 am by Mechatrommer »
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Offline soldar

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Re: Trying to prove a point
« Reply #40 on: June 08, 2019, 10:43:14 am »
Does a device have an electrical state when power is not applied?
Doesn't an "electrical state" imply existence of ....electricity?

Or to put in in other words, what's the weight of an elephant with no gravity "applied"?
If a man talks but his wife is not there to hear him, is he still wrong? :)
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Offline Cerebus

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Re: Trying to prove a point
« Reply #41 on: June 08, 2019, 05:25:44 pm »
If a man talks but his wife is not there to hear him, is he still wrong? :)

I've checked with the Mrs. and the answer is "Yes".

Back to the, according to the Mrs., much less important issue of the two questions presented as examples.

If the person who set them can't see why they are very badly written questions then they should be sent off for some remedial education themselves. If they actually know that they are terrible questions, but insist on still defending themselves to their students when they point out the inadequacies of those questions they should get the hell out of education as a career. Still claiming to be right, when proven wrong, is a disqualifier for almost any occupation except hermit or politician.
Anybody got a syringe I can use to squeeze the magic smoke back into this?
 
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Offline Nominal Animal

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Re: Trying to prove a point
« Reply #42 on: June 08, 2019, 06:09:44 pm »
I agree with what Cerebus wrote above, even though I recommend a softer initial approach.

That is, I still believe one should start with the assumption that it is a miscommunication and not an error.  Doing that in my experience makes others do that too, and therefore the quality of the information exchange rises, and that is excellent value for small effort.  Me fail English often myself when I get excited or tired, and no matter of remedial education seems to fix that.  However, when the error is proven (as it has in various posts in this thread), refusal to correct that error means nothing that person says can be taken at face value anymore.
« Last Edit: June 08, 2019, 06:11:19 pm by Nominal Animal »
 

Offline bson

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Re: Trying to prove a point
« Reply #43 on: June 08, 2019, 06:13:14 pm »
I don't like such questions. Why can't they put it as "what is default state of a normally open (momentarily) switch"? Looks like they over-complicate things just to pan students. Why doing this? Give knowledge, not frustration.
In a sense yes, but it's also about reading comprehension, paying attention to detail, and context.  Such as, what is a switch.  A switch closes two contacts.  In the absence of other information, that is what a switch is.  Hence, C or any other talk of applying power is irrelevant.  A relay is a coil-actuated switch, but there is no talk of coils or relays here.  Just a switch.  Nor do coils or power need to be introduced to answer the question.  Questions like this teach students to work with the information provided, not go off and imagine something other than what's actually stated.  This is a critical cognitive engineering skill, because 99% of the time PMs will come with a poor explanation of a problem that requires clearing up before proceeding to find a solution, along with a proposed solution (that should be courteously accepted but doesn't need to make it further than your inbox).  It's a pretty basic critical reasoning skill.
« Last Edit: June 08, 2019, 06:23:47 pm by bson »
 
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Online ebastler

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Re: Trying to prove a point
« Reply #44 on: June 08, 2019, 07:13:20 pm »
Why can't they put it as "what is default state of a normally open (momentarily) switch"?

Yeah, or even better: "What is the normal state of a normally open switch?"  :P

The standards at school are not quite that low, I think...  ;)
 

Offline soldar

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Re: Trying to prove a point
« Reply #45 on: June 09, 2019, 11:49:12 am »
Yeah, or even better: "What is the normal state of a normally open switch?"  :P

How about "You are asked what is the normal state of a normally open switch, can you check 'open' in the choices given to the right?"
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Offline Psi

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Re: Trying to prove a point
« Reply #46 on: June 09, 2019, 11:53:01 am »
Yep, question is trying to confuse you.
Need to read it carefully and not jump to any conclusions.

That's pretty common with multichoice questions.
When creating multichoice questions the test writer has to be careful they don't give away the answer by simply having it as an option.
So they make it a bit confusing and have multiple correct answers and you have to carefully figure out what exactly the question is asking.
« Last Edit: June 10, 2019, 12:43:26 am by Psi »
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Offline tpowell1830

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Re: Trying to prove a point
« Reply #47 on: June 09, 2019, 10:50:11 pm »
Ok, I will throw my 2 cents into this discussion, since I have been a successful electrical engineer since well before the turn of the century. The use of the word "power" is ambiguous in nature, since power is a measure of watts. However, even if the question used the term EMF or Voltage, it does not apply in the case of the syntax of the question. So, all answers with the word "power" in them are ambiguous. Further ambiguous is the term in question "electrical state", which NO and NC does not apply to any electrical state when a switch is normally open or normally closed. NO and NC apply to the physical condition of a switch that is not actuated, period, whether it is a relay or a manual switch. In the case of a solid state relay, the same is true, even though the active part of the switch is not a contact. As someone earlier posted, there are conditions that are spelled out on the schematic where a switch can be NO, but held closed on machinery, and the same with NC, held open, but this is not even in the ballpark of the syntax of the question.

The abbreviations NO (normally open) and NC (normally closed) represent the electrical state of
switch contacts when
A. power is applied
B. the switch is actuated
C. power is not applied
D. the switch is not actuated

BTW, my answer would be "D." in all cases.

Hope this helps...

EDIT: If voltage is not applied, there is no "electrical state", just sayin'.
« Last Edit: June 09, 2019, 10:54:54 pm by tpowell1830 »
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Offline jmelson

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Re: Trying to prove a point
« Reply #48 on: June 09, 2019, 11:35:59 pm »
:blah: he says the only correct answer is c and refuses to accept that he is wrong, and let me tell you it's not the only question he made that had several correct answers... He's such a stubborn guy... I like him as a person just not as a teacher
Forget everything you learned in this class (unless you can verify it elsewhere), this guy doesn't know what he is talking about.
if this is a university or tech college, report this to higher ups, it really is not good that he is giving his incorrect understanding to a class full of students.

If you want corroboration, look up switch info on a manufacturer's web page, the makers of switches have been using this terminology for well over 100 years!  Or, see :
https://en.wikipedia.org/wiki/Switch  in the section on "Contact terminology".  They correctly state that the NO or NC designation has NO reference to POWER, but only to whether the contacts are touching or not touching!

Jon
 

Offline DimitriP

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Re: Trying to prove a point
« Reply #49 on: June 10, 2019, 12:50:06 am »
Quote
The abbreviations NO (normally open) and NC (normally closed) represent the electrical state of
switch contacts when
A. power is applied
B. the switch is actuated
C. power is not applied
D. the switch is not actuated


Dear everyone, the question as posed ( whether it's an appropriately phrased for the intent or not ) includes the magic phrase "electrical state".
Everyone that says D, is not answering the question as worded, but answering the "intent" of the question instead.
Out of the four possible answers, there is only one single, solitary, lonesome answer that involves the "electrical state" of the switch and that's when electricity is present.
No electricity, no electrical state. 
Either way in my book it justifies a "your question doesn't mean what you think it means" tshirt .
   If three 100  Ohm resistors are connected in parallel, and in series with a 200 Ohm resistor, how many resistors do you have? 
 


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