| Electronics > Beginners |
| Trying to prove a point |
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| brabus:
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?). |
| DDunfield:
--- Quote from: dietert1 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. --- End quote --- 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 |
| DDunfield:
--- Quote from: brabus on June 07, 2019, 09:11:08 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?). --- End quote --- 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. |
| DimitriP:
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"? |
| DDunfield:
--- Quote from: DimitriP 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? --- End quote --- 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"? --- End quote --- That's an easy one: 0 The mass however remains the same. Dave |
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