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Old 02-09-2009, 08:57 PM
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Gdrumm Gdrumm is online now
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Default What is infinite resistance?

I'm trying to solve a series circuit question from my DC Circuits class homework, and I can't seem to recall what infinate resistance means.

Here is the info I have on the circuit.
E=40v, R1=5ohms, R2=10ohms, R3= Infinate ohms.

I see the answer in the back of the book, but I don't know how they got it.

I'm solving for E Total, I Total, R Total, and P Total.

I'm guessing that infinate resistance means there is a short?
Thanks, Gary
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Old 02-09-2009, 09:01 PM
KL7AJ KL7AJ is offline
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Quote:
Originally Posted by Gdrumm View Post
I'm trying to solve a series circuit question from my DC Circuits class homework, and I can't seem to recall what infinate resistance means.

Here is the info I have on the circuit.
E=40v, R1=5ohms, R2=10ohms, R3= Infinate ohms.

I see the answer in the back of the book, but I don't know how they got it.

I'm solving for E Total, I Total, R Total, and P Total.

I'm guessing that infinate resistance means there is a short?
Thanks, Gary
Nope...infinite resistance means the component (resistor) does not exist. You may safely remove it from your schematic with no danger of punishment
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Old 02-09-2009, 09:55 PM
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Thanks,
But I'm still curious, because in the answer section of my workbook, it shows Total I=0 amps, meaning that R3 in effect neutralized R1 and R2.

So, does this look accurate?
ET = 40v
IT = 0A
RT = 00 ohms
PT = 0 watts

What does "fail open" mean?
I found that on this site, Vol 1, Chapter 5/7.
It implies that a resistor might "fail open", increasing it to near infinate levels.
Thanks, Gary

Last edited by Gdrumm; 02-09-2009 at 10:05 PM.
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Old 02-10-2009, 12:28 AM
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If the resistors are connected in series then no current will flow due to the infinite resistance (open circuit).

if the resistors are connected in parallel then current will flow only through R1 and R2.
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Old 02-10-2009, 12:55 AM
flat5 flat5 is offline
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"fail open" means resistor has been destroyed. It has failed.
In this case, "fail open", it does not pass any current anymore.
It is a dead resistor. Don't try to return it to the store where you bought it.

See "Monty Python Dead Parot Sketch".
http://www.youtube.com/watch?v=e6Lq771TVm4
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Old 02-10-2009, 05:11 AM
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I=E/R, so as R increases, I diminishes. As R increases without bound, I approaches zero. Once R is a few zillion yotta-Ohms, I is a few zillionths of a yocto-Ampere.
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Old 02-10-2009, 02:06 PM
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Quote:
Originally Posted by Gdrumm View Post
I'm trying to solve a series circuit question from my DC Circuits class homework, and I can't seem to recall what infinate resistance means.

Here is the info I have on the circuit.
E=40v, R1=5ohms, R2=10ohms, R3= Infinate ohms.

I see the answer in the back of the book, but I don't know how they got it.

I'm solving for E Total, I Total, R Total, and P Total.

I'm guessing that infinate resistance means there is a short?
Thanks, Gary
Infinite resistance is open circuit (burnt resistor in real life) no current will flow, zero ohms is short circuit.
Lets not confuse.
Brian
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