Timeline for Why is the current the same across these resistors?
Current License: CC BY-SA 4.0
17 events
| when toggle format | what | by | license | comment | |
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| Nov 4, 2022 at 13:42 | answer | added | Devesh Kumar Singh | timeline score: 0 | |
| Nov 1, 2022 at 4:05 | comment | added | user57037 | @RamblinWreck, I don't know. For this particular circuit it is easy to solve for V+ first using the 0 amps assumption. Then assume V- = V+ (because there is negative feedback). Then it is really easy to solve for i1 (2V / 2k). It is fine if your way is easier for you. But I think the conventional way works well too. | |
| Oct 31, 2022 at 22:09 | comment | added | Ramblin Wreck | The "assume input current is zero" approach has always bothered me, because under that assumption you can easily draw a KCL to show that the current through the 5k resistor is also zero...and same for the 2k. I prefer to use the equivalent circuit for an ideal op amp and then work out the voltages/currents from there using node analysis equations. | |
| Oct 31, 2022 at 18:00 | history | tweeted | twitter.com/StackElectronix/status/1587142392922128394 | ||
| Oct 31, 2022 at 15:46 | answer | added | Audioguru | timeline score: 0 | |
| Oct 31, 2022 at 13:36 | history | edited | spuder | CC BY-SA 4.0 |
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| Oct 31, 2022 at 12:44 | history | became hot network question | |||
| Oct 31, 2022 at 10:21 | answer | added | feynman | timeline score: 2 | |
| Oct 31, 2022 at 10:04 | history | edited | ocrdu | CC BY-SA 4.0 |
added 118 characters in body; edited tags
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| Oct 31, 2022 at 7:36 | answer | added | user57037 | timeline score: 3 | |
| Oct 31, 2022 at 7:28 | comment | added | user57037 | If it turns out that the current is negative, then you can just reverse the direction: all charges which flow into the 2 k resistor have no choice but to carry on through the 5 k resistor. | |
| Oct 31, 2022 at 7:27 | comment | added | user57037 | One of the assumptions of op-amp circuits (given that there is negative feedback) is that no current flows into the op-amp input. Therefore all the charges which flow into the 5k resistor have no choice but to continue on through the 2k resistor. They are not allowed to take the alternate path into the op-amp. This is what the person means when they say that the currents must be the same. | |
| Oct 31, 2022 at 7:22 | answer | added | bobflux | timeline score: 9 | |
| Oct 31, 2022 at 4:58 | comment | added | Hearth | Why do you say there's 2 V across the 5 kΩ resistor? There's not. | |
| Oct 31, 2022 at 4:46 | comment | added | Spehro 'speff' Pefhany | Current is not across, current is through. Remember all currents into a node add up to zero (when consistent direction is used) by Kirchhoff's Current Law. | |
| Oct 31, 2022 at 4:39 | comment | added | Bryan | To intuit the answer: ask yourself how much current is flowing in or out of the negative terminal of the opamp. | |
| Oct 31, 2022 at 4:35 | history | asked | spuder | CC BY-SA 4.0 |