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What terms are correct for describing the resistance of an open circuit?


kioolt

Open circuit resistance  

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Do to a recent thread on this forum, I thought it would be a good idea to see what most people believe is the correct term or terms for describing the electrical resistance an open electrical circuit. Please give a short explanation of your choice. You may choose more then one selection.

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Do to a recent thread on this forum, I thought it would be a good idea to see what most people believe is the correct term or terms for describing the electrical resistance an open electrical circuit. Please give a short explanation of your choice. You may choose more then one selection.

 

Evening Kioolt

 

The common understanding of an open circuit resistance is (R = infinity) but depending on how far the open is & the humidity of the air around the open there is probably a slight measurable amount with the right equipment.

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Dirtrider,

 

I should have probable said for all practical purposes. I don't think I've ever seen any equipment that could measure the resistance of air but it probable does exist somewhere. But you are correct.

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For the person or persons that voted zero resistance and no resistance could you please tell me what you think a short circuit measures?

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Shiny Side Up
For the person or persons that voted zero resistance and no resistance could you please tell me what you think a short circuit measures?

Could it be this:

If there is no complete circuit - then no notable resistance can be measured. (i.e. attempting to measure ground continuity between the ngative battery post and a disconnected gnd wire?) This is really "no continuity". But I do see what you're getting at with "infinite resistance".

A short is current bypassing an intended load and continuing to gnd, thereby blowing a fuse or the intended load not functioning.

I'm NOT an electronic engineer - just a guy trying to live in everybody else's world...

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I went with infinite, but it is really sort of voltage dependent. You'd think a gap from the ground to a cloud would be open enough to prevent an arc, but...

 

Could it be this:

If there is no complete circuit - then no notable resistance can be measured. (i.e. attempting to measure ground continuity between the ngative battery post and a disconnected gnd wire?)

 

Hopefully that ground wire is disconnected at both ends, otherwise your meter probably just completed the circuit. Yes, the meter doesn't put out enough voltage to jump an air gap so an open circuit will show as infinite resistance (no needle movement) on an analog meter or open circuit on a digital meter. I think the confusion in people's brains is that no reading doesn't equate to no resistance, it equates to no circuit the meter is capable of measuring.

Edited by rxcrider
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Actually an open circuit does not give you no reading. The OL on my digital meter is a reading. It means over limit. The non movement of the needle on an analog is also a reading. It also could be interpreted as over limit. Out of range of the capabilities of the meter. But it definitely does not mean no or zero resistance. The OL on my digital meter means over 2 megohms. It's reading resistance even before you try to test the swtich, coil, etc. That's not zero or no resistance.

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Actually an open circuit does not give you no reading. The OL on my digital meter is a reading. It means over limit. The non movement of the needle on an analog is also a reading. It also could be interpreted as over limit. Out of range of the capabilities of the meter. But it definitely does not mean no or zero resistance. The OL on my digital meter means over 2 megohms. It's reading resistance even before you try to test the swtich, coil, etc. That's not zero or no resistance.

 

Correct - I should have said no change in reading does not equate to no resistance. And why do I keep reading OL as open line instead of over limit - I really should remember that I've learned this a few times already. For that matter, the pegged needle on the analog meter doesn't say infinite either, just some max that it is capable of measuring. In all my entire post was in the correct spirit with a whole bunch of errors. Brilliant.

Edited by rxcrider
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I went with infinite, but it is really sort of voltage dependent. You'd think a gap from the ground to a cloud would be open enough to prevent an arc, but...

Yes voltage plays its part since we see arcs in the sky with lightning, but this is extremely high voltage and actually corresponding low current (relatively speaking) due to the very high resistance of the air as measured by our simple 9vdc meters. :grin:

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I'm curious as to your curiosity about people's (mis)understanding of electricity. You're not asking an objective question. You're asking people what they THINK they know about a particular topic.

 

It's probably a good bet that most people will not know the answer. I'll hypothesize that people who don't know the answer are likely to avoid the poll. At the same time, it seems reasonable that people on this forum are more likely to know the answer (for a variety of reasons).

 

I know the answer to the poll question, but I didn't vote. There's probably a lot of us out there. :wave:

 

Achieving a meaningful poll gets complicated quickly. So what is it you're trying to learn here?

 

 

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I'm not really try to learn anything here. I was hoping that the poll would stir up a conversation to teach people. I've got another poll going about the reason for resistors when using LED turn signal bulbs. At this time more people are getting it wrong then right. There is a small discussion going on there. The only people commenting are the ones that got it right.

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Yes voltage plays its part since we see arcs in the sky with lightning, but this is extremely high voltage and actually corresponding low current (relatively speaking) due to the very high resistance of the air as measured by our simple 9vdc meters. :grin:

 

Not exactly. Lightning is many millions of volts and many thousands of amps. But for a extremely short time (milliseconds). Google it for more info.

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roger 04 rt
Do to a recent thread on this forum, I thought it would be a good idea to see what most people believe is the correct term or terms for describing the electrical resistance an open electrical circuit. Please give a short explanation of your choice. You may choose more then one selection.

 

Evening Kioolt

 

The common understanding of an open circuit resistance is (R = infinity) but depending on how far the open is & the humidity of the air around the open there is probably a slight measurable amount with the right equipment.

 

+1, the only proper way to describe an open circuit is: open circuit or infinite resistance. Terms like zero, nada, no, zilch, etc describe a short circuit.

 

In an open circuit, when you apply, a voltage zero current flows. In a short, when you apply a current, no voltage is produced; or if you apply a voltage, the maximum current of that voltage source will flow, usually with dramatic results.

Edited by roger 04 rt
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... In a short, when you apply a current, no voltage is produced; or if you apply a voltage, the maximum current of that voltage source will flow, usually with dramatic results.

 

To be pedantic, the current that will flow in a short circuit (or any circuit for that matter) for a given voltage is dependent on the resistance in the circuit (Ohm's law...current (amps) = voltage divided by resistance). Even a short circuit has some resistance altho it might be very very tiny, usually not measurable by even expensive ohmmeters. In some cases the limiting factor is the internal resistance of the source, a battery or generator etc.

 

No question, tho...a short circuit across a substantial supply will often be quite dramatic.

Edited by MarkAZ
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I remember years ago when I was working on an electric lift truck. The operator of the lift truck insisted that the problem was the battery plug. The lift truck wouldn't travel but the mast would work. The operator said if I shake the battery plug by operating the mast it well then travel. I explained to him that the mast wouldn't operate either if it was the battery plug. He was actually shaking the whole lift truck when he operated the mast. But to him it was only the battery plug he was shaking. While on one side of the lift truck the operator thought he was going to show me he was right by prying on the battery plug with a big piece of wood. Before I could stop him the battery plug broke and the two battery wires shorted. I ran because I thought the battery might blow up. You should have seen the sparks. These batteries are about 4 feet by 4 feet by 3 feet.

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Yes voltage plays its part since we see arcs in the sky with lightning, but this is extremely high voltage and actually corresponding low current (relatively speaking) due to the very high resistance of the air as measured by our simple 9vdc meters. :grin:

 

Not exactly. Lightning is many millions of volts and many thousands of amps. But for a extremely short time (milliseconds). Google it for more info.

I stand somewhat corrected. :grin:

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..... Please give a short explanation of your choice. ....

 

Actually, would be an "open" explanation.

 

har har har

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