All About Circuits Forum What is infinite resistance?
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#1
02-09-2009, 08:57 PM
 Gdrumm Senior Member Join Date: Aug 2008 Location: Dallas, Texas Posts: 432
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
#2
02-09-2009, 09:01 PM
 KL7AJ E-book Developer Join Date: Nov 2008 Location: North Pole, Alaska Posts: 1,547

Quote:
 Originally Posted by Gdrumm 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
__________________
REAL men don't need voltmeters.
#3
02-09-2009, 09:55 PM
 Gdrumm Senior Member Join Date: Aug 2008 Location: Dallas, Texas Posts: 432

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.
#4
02-10-2009, 12:28 AM
 mik3 Senior Member Join Date: Feb 2008 Location: Cyprus, but now in UK (GMT+0) Posts: 4,846 Blog Entries: 9

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.
#5
02-10-2009, 12:55 AM
 flat5 Senior Member Join Date: Nov 2008 Posts: 252

"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
#6
02-10-2009, 05:11 AM
 thingmaker3 Super Moderator Join Date: May 2005 Location: Rural, Oregon GMT -8 Posts: 5,072 Blog Entries: 6

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.
__________________
"I want to establish in your mind very clearly that you must not think I deny all that I do not admit. On the contrary, I think there are many things which may be true, and which I shall receive as such hereafter, though I do not as yet receive them; but that is not because there is any proof to the contrary, but that the proof in the affirmative is not yet sufficient for me"
- Michael Faraday
#7
02-10-2009, 02:06 PM
 blhoward New Member Join Date: Feb 2009 Location: Willow River BC Canada GMT-8 Posts: 5

Quote:
 Originally Posted by Gdrumm 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

 Tags infinate, infinite, resistance

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