Author Topic: Trying to prove a point  (Read 5497 times)

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Offline CoopedUpTopic starter

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Trying to prove a point
« on: June 06, 2019, 07:37:56 pm »
So I'm not really a beginner but I figured this was the best place to put this. I had a packet for a class and this was a question on it. I want to prove to my teacher that he is wrong by having a poll I guess you could say of what answer you guys think it is and if I'm wrong I guess you can explain to me how I am wrong. I'm not going to say anything about what my answer is but just let me know.

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
 

Offline ejeffrey

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Re: Trying to prove a point
« Reply #1 on: June 06, 2019, 07:43:06 pm »
D for a mechanical switch, potentially C for a relay as long as you are clear that is is power to the coil not to the switch contacts.
 

Online mikerj

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Re: Trying to prove a point
« Reply #2 on: June 06, 2019, 07:46:03 pm »
With the context provided in the question the answer has to be D.
 

Offline dietert1

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Re: Trying to prove a point
« Reply #3 on: June 06, 2019, 07:49:26 pm »
I guess it should be D.
If the switch gets actuated by an electro magnet (like in a relay), then C may be correct, too: The switch is not actuated as long as power is not applied to the coil.

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Offline bsudbrink

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Re: Trying to prove a point
« Reply #4 on: June 06, 2019, 07:51:15 pm »
A little vague, but D.
 

Offline DimitriP

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Re: Trying to prove a point
« Reply #5 on: June 06, 2019, 07:55:33 pm »
Just to stirr things up.......    A !

   If three 100  Ohm resistors are connected in parallel, and in series with a 200 Ohm resistor, how many resistors do you have? 
 

Online ataradov

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Re: Trying to prove a point
« Reply #6 on: June 06, 2019, 07:58:27 pm »
I don't get it. It says right in the name "normally". Normally open is always normally open, not matter what.

But yes, it looks like they meant D.

And that's exactly what I hate about those theoretical academia questions.
« Last Edit: June 06, 2019, 08:00:05 pm by ataradov »
Alex
 

Offline SparkyFX

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Re: Trying to prove a point
« Reply #7 on: June 06, 2019, 08:03:56 pm »
What ejeffrey said.

From vocational training i think i remember that position switches might be drawn in the initial condition of a machine - its mechanical state in which the machine is supposed to run in (e.g. housing/tamper evidence switch, NO, but drawn closed).
"Normally" therefore refers to unactuated (as in holding it in hand), but a wiring diagram might show the normal mechanical state of the machine it is in.
Depending on which symbols are to be used, it might be possible to include the type and direction of actuation in the diagram, giving away the clue if it is actuated in this state.
« Last Edit: June 07, 2019, 04:03:08 am by SparkyFX »
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Offline larrybl

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Re: Trying to prove a point
« Reply #8 on: June 06, 2019, 08:30:02 pm »
Yes to Sparkly, I answered E-None of the above. From my diagram
Pedal Up = NO
Clutch OFF = NC
Not Occupied = NC

The state of a switch in a diagram should be clarified.
 

Offline StillTrying

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Re: Trying to prove a point
« Reply #9 on: June 06, 2019, 08:52:09 pm »
The answer has to be D. the switch is not actuated

C. power is not applied, is possibly a trap to check that you've read the question accurately, we all think "relay" when relay isn't mentioned anywhere, although it's always possible that the question writer doesn't know the difference.

If I had put D and the supposed correct answer was C, I wouldn't let them get away with it!
.  That took much longer than I thought it would.
 

Offline DDunfield

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Re: Trying to prove a point
« Reply #10 on: June 06, 2019, 09:24:24 pm »
The question says switch, as do two of the possible answers, so I would say 'D'.
Worth noting that 'D' covers off a relay as well.

One could argue that if you keep your computer on almost all the time, then it's switch is "normally" closed, however by convention the term "normally" applied to an electrical switch indicates it's position in a deactivated position.

Light switch - deactivated is open, so it's "normally open".

Reed sensor in a intrusion alarm, deactivated means loop not broken (closed), so it's "normally closed".

Dave

PS: What did the teacher say was the correct answer?
 

Offline neil t

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Re: Trying to prove a point
« Reply #11 on: June 06, 2019, 11:06:01 pm »
If no diagram of the switch unit is supplied your teacher has asked a stupidly vague question, all the multiple answers are possible dependant on the type of unit.
 

Offline JxR

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Re: Trying to prove a point
« Reply #12 on: June 06, 2019, 11:13:45 pm »
You didn't say what your answer was.  How can we tell you if your wrong or right?  Like everyone else said, the answer is D.

This shows alot of pictures, while I only scanned it nothing immediately wrong stood out.  Maybe it will help if your answer was not D.

https://www.electronicshub.org/switches/
« Last Edit: June 06, 2019, 11:18:31 pm by JxR »
 

Offline DDunfield

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Re: Trying to prove a point
« Reply #13 on: June 07, 2019, 01:59:46 am »
Also worth mentioning that it's fairly unusual to see N.O and N.C. applied to switches which have two steady-states (toggle), since these can be used in either capacity. If it does appear it will be describing the switch function in the circuit, not the physical switch itself.

The nomenclature is usually applied to switches which must be held in the active state, such as momentary push buttons, spring levers and relays.

Dave
 

Offline CoopedUpTopic starter

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Re: Trying to prove a point
« Reply #14 on: June 07, 2019, 03:05:14 am »
 :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
 

Offline CoopedUpTopic starter

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Re: Trying to prove a point
« Reply #15 on: June 07, 2019, 03:16:06 am »
And of course I picked D because it applyable to most switches. Another question asks
A(n)______ converts light energy directly into electric energy

A. phototransistor
B. solar cell
C. photoconductive cell
D. LED

I wrote on the test that I'm sure all of them produce electricity when light is shown on them but I can personally vouch that b and d are correct. And his response was LEDs don't produce electricity when a light is on it... But they do and he's and electrical engineer... And he refuses to give me point because God forbid he's wrong
 

Offline L_Euler

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Re: Trying to prove a point
« Reply #16 on: June 07, 2019, 03:18:35 am »
He didn’t happen to explain what happens to the switch when power is applied did he?
There's no point to getting old if you don't have stories.
 

Offline CoopedUpTopic starter

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Re: Trying to prove a point
« Reply #17 on: June 07, 2019, 03:20:01 am »
His only explanation had something to do with a home switch in a cnc but it wasn't correct
 

Offline Gregg

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Re: Trying to prove a point
« Reply #18 on: June 07, 2019, 04:05:15 am »
For a relay, C is a subset of D.  If power applied means to the relay coil; the question does not state this. A rational person reading the question does not know what is meant by “power applied”; therefore choice D is far more rational and correct for more switching situations.

For a manual switch, choice C doesn’t make any sense when considered as an answer to the stated question.  However, D makes more sense than C but the question is very vague and flawed.

The question should be:
The abbreviation NO (normally open) represents the electrical state of:
OR
The abbreviation NC (normally closed) represents the electrical state of:

The teacher is trying to combine two questions into one; without a suitable answer. 

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Offline ejeffrey

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Re: Trying to prove a point
« Reply #19 on: June 07, 2019, 04:23:15 am »
And of course I picked D because it applyable to most switches. Another question asks
A(n)______ converts light energy directly into electric energy

A. phototransistor
B. solar cell
C. photoconductive cell
D. LED

I wrote on the test that I'm sure all of them produce electricity when light is shown on them but I can personally vouch that b and d are correct. And his response was LEDs don't produce electricity when a light is on it... But they do and he's and electrical engineer... And he refuses to give me point because God forbid he's wrong

OK, on that one you are just being a pain in the ass.  The answer is clearly B, and saying anything else is stupid even if in some situations the other devices can do it.  That is why most multiple choice exams state "circle the best answer" or similar at the top.  The best answer to that question is B, and I would absolutely not give you a point for any other answer.
 

Offline garethw

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Re: Trying to prove a point
« Reply #20 on: June 07, 2019, 05:48:51 am »
D. [emoji3]


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Offline Mechatrommer

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Re: Trying to prove a point
« Reply #21 on: June 07, 2019, 08:26:19 am »
: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
i'm a teacher by proffesion for already 15 years. my answer is that, thats not a good question, its called ambiguous question. since in order to actuate a switch (relay) you need to apply power, hence not actuated = power not applied, answer either C or D should be correct (from my understanding and experience). the problem with teacher, esp young teachers, albeit they are good at teaching, not necessarily good at making questions. good questions need to be peer reviewed, if we get different answers from different teachers in the same subject, that means its a flag that the question is ambiguous. different students/readers have different experience, we need to rule that out so everybody with good knowledge from various discipline should end up with the same answer. if ambiguous questions already given to students in a test we teachers in the panel usually end up with 2 or more correct answers before marking. tell this to your teacher, or better tell this to the other teachers in the same subject so they can advice their peer. some teachers are usually too ego to get advice from their student. ymmv.
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Offline dietert1

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Re: Trying to prove a point
« Reply #22 on: June 07, 2019, 08:52:35 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.

Regards, Dieter
 

Offline DDunfield

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Re: Trying to prove a point
« Reply #23 on: June 07, 2019, 09:00:43 am »
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

The only way I could see this being even partially correct is because the original question says "electrical state".

A normally-open button, not pressed has it's contacts open whether or not power is applied.
A normally-closed button not pressed has it's contacts closed whether or not power is applied.

It appears your teacher is looking at it in terms of current flow (electrical state?):

N.O. button is an open circuit when power is applied.
N.C. button is a closed circuit when power is applied.

A "trick" question that has very little to do with actual knowledge.

EDIT: Just re-read the original, C is "power is NOT applied". So I don't see any way for C to make sense. The above would argue (albeit weakly) for A "Power is applied".

Dave
« Last Edit: June 07, 2019, 10:08:21 am by DDunfield »
 

Offline exe

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Re: Trying to prove a point
« Reply #24 on: June 07, 2019, 09:02:08 am »
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.
 


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