46 votes
Accepted

How did scientists deal with electronics' problems before Kirchhoff and Ohm's laws?

This is a bit like asking how Aztecs built cars without the wheel: they didn't. There was a chain of invention by scientists in the early 1800s building off each others work. Prior to then there was ...
pjc50's user avatar
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21 votes
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What is wrong about this application of Kirchhoffs Current Law?

Professor is wrong. The correct answer is 2A. I solved it algebraically just as every one else, 4=3+Ic+-1, Ic = 2. A DC simulation in Spice yields 2A as as well.
Doug Crowe's user avatar
17 votes
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Solving an ideal opamp-circuit leads to a contradiction

The error is in the assumption the I2 = I1. The OpAmp can (in general) sink and source current. When it would be sourcing current, this current would have to go to ground, either through R2 or through ...
Huisman's user avatar
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16 votes
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Mysterious energy disappearance of capacitors

The simple answer is that you cannot short circuit two ideal voltage sources without creating an over determined system of equations. So if you try to use network theory to describe the circuit you ...
Felix S's user avatar
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12 votes

Trouble understanding when voltages get split

Just re-draw the schematic, slightly: simulate this circuit – Schematic created using CircuitLab (Note that your confusion about "Would the 9V be split between these two resistors?" completely ...
jonk's user avatar
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12 votes

Is it possible for the system of equations of an electric circuit to not have a unique solution?

So long as you consider networks containing only positive-valued linear resistors, ideal voltage sources, and ideal current sources (and you don't put two current sources in series or two voltage ...
The Photon's user avatar
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12 votes
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A circuit cannot contain two different currents in series; otherwise KCL will be violated

Here is the circuit we understand you to mean when you say "two currents in series": simulate this circuit – Schematic created using CircuitLab For I2 to be a 2 A current source, 2A ...
The Photon's user avatar
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11 votes
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Does this experiment show that Kirchhoff's Law hold when there's a changing magnetic field involved in a circuit?

The lumped component models to which KVL is applied are just that--models. Like all models, they are only accurate to the extent that they represent the relevant characteristics of the system they ...
ajb's user avatar
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11 votes

Can two voltmeters connected to the same terminals show different values? Circuit with induced EMF

YES, two voltmeters connected to the very same couple of terminals can simultaneously show two different values. The reason is that, since the circuit path is enclosing a variable magnetic flux region,...
Sredni Vashtar's user avatar
11 votes
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Textbook's way of determining KVL polarities

Actually, it does not matter. It is kind of an arbitrary assumption. You just make a assumption about polarity. If the result is negative, then just change your decision to the opposite. Let choose ...
anilberg's user avatar
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10 votes
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Is it possible to have a resistor network whose total value is unsolvable?

If you have two terminals to a network of resistors, the resistance between the two terminals will always be a single value. This is a special case of Thevenin's Theorem, without the complicating ...
Neil_UK's user avatar
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9 votes

Circuit yields a peculiar contradiction between KCL, KVL and Faraday's law

The wrong assumption is that any point on the wires 'A' and 'B' are equivalent and that they constitute discrete "nodes". If you have a straight wire segment in a changing magnetic field, there will ...
Evan's user avatar
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9 votes

What is wrong about this application of Kirchhoffs Current Law?

I agree, it should be 2A. I don't know how it could be 8A
Voltage Spike's user avatar
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9 votes

How to handle four resistors in a square (OP-amp)?

Just look at this circuit. what I have done is that since both R3-R1 and R4-R2 are going to ground , I split it into two separate path flowing to ground. Now you can just re draw it and observe the ...
Hari Krishna's user avatar
9 votes
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Mistake in using KVL and KCL in ideal opamp-circuit

Jan, I don't see any need for the opamp power sources and their currents in this schematic (in some others cases, I might.) So I don't think that's an important insight here. Here's the schematic ...
jonk's user avatar
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8 votes

Mysterious energy disappearance of capacitors

If you build this circuit in reality, there is some resistance. Half the energy provided by the battery is stored in the capacitor and half of it is turned into heat in the resistor. You would think ...
user253751's user avatar
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8 votes

Mysterious energy disappearance of capacitors

This is called the two capacitor paradox. It is the reason charge pumps can not be 100% efficient. Although you have a battery instead of a capacitor, the problem is essentially the same. If you like, ...
Phil Frost's user avatar
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8 votes
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voltage direction confusion

Not notoriously trivial because the reason is notoriously silly. Benjamin Franklin did not know what actually moved to carry electricity so had to guess a polarity for each charged component. He ...
DKNguyen's user avatar
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8 votes

A circuit cannot contain two different currents in series; otherwise KCL will be violated

Consider two pumps connected with one sending 5 gallons per minute to the other that passes 2 gallons per minute. How can that happen?
stretch's user avatar
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8 votes
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How to analyze this RC circuit without finding Thévenin's equivalent circuit?

KCL Here's your re-drawn schematic (I'm in the practice of re-drawing schematics as a rule): simulate this circuit – Schematic created using CircuitLab My KCL sets up like this (treating your ...
jonk's user avatar
  • 77.9k
7 votes

Circuits explained without analogies

You don't want analogies since I've heard that those analogies break down when we get to more complex circuits. Yes, the models fall apart, just like Newtonian physics don't work when you get to ...
Oldfart's user avatar
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7 votes
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Is there any way to simplify this circuit?

Never underestimate the power of using your eyes and redrawing stuff to remove clutter. Making stuff de-cluttered makes things simpler and allows you to find an answer. Here's a simple helping hand ...
Andy aka's user avatar
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7 votes

Mistake in using KVL and KCL in ideal opamp-circuit

You've made a mistake in accounting for the supply current that flows to the op amp. It's almost certainly easier to start with a fresh set of equations as jonk's answer does, but it's also ...
nanofarad's user avatar
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7 votes

A circuit cannot contain two different currents in series; otherwise KCL will be violated

As you say you need to be spoon-fed, I need to make a number of observations. 'Ideal' components are abstractions, simplified models of the real world, that are sometimes not too intuitive. Ideal ...
Neil_UK's user avatar
  • 166k
7 votes

Determining currents in each part of the circuit using Kirchhoff 's laws

Your equations look correct to me. Congratulations on keeping resistor voltage polarities consistent with current direction labels, that's usually where people mess up. Your question, though, is not ...
Simon Fitch's user avatar
  • 35.2k
6 votes

How did scientists deal with electronics' problems before Kirchhoff and Ohm's laws?

Before tubes or semiconductors were used there was no electronics science, only electric science did exist. When Georg Simon Ohm discovered the laws of electrical resistance, he needed voltage ...
Uwe's user avatar
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6 votes

Should Kirchhoff's Law be changed to account for information removal?

Kirchhoff's laws are a huge simplification of Maxwell's equations under some very specific assumptions (lumped elements, quasi-static fields, etc.). Hence they are part of classical physics, as ...
LorenzoDonati4Ukraine-OnStrike's user avatar
6 votes
Accepted

Circuit doesn't seem to add up under Kirchhoff's laws

You actually have two problems right now, but let's just talk about one first (the one you are somewhat aware that you have. You seem to be oblivious to the other one right now but we'll get to it ...
DKNguyen's user avatar
  • 56.7k
6 votes
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How can Kirchoff current and voltage law be applied here

Preface I recommend early and continual practice at redrawing circuits to novitiates in electronics. It's an essential skill and it takes regular practice in order to yield some of its greater powers. ...
jonk's user avatar
  • 77.9k
6 votes

Nodal Analysis - Kirchoffs Current Law

Preface note: I originally used \$3\:\text{A}\$ as the current source. But I mis-read the problem, as stated. They specify, on the schematic, that the out-flowing current source value is \$-3\:\text{A}...
jonk's user avatar
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