Questions tagged [electric-circuits]

An electronic system, with closed loop current flow, and relative electrical potentials present across electrical components.

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118 votes
2 answers
89k views

On this infinite grid of resistors, what's the equivalent resistance? [closed]

I searched and couldn't find it on the site, so here it is (quoted to the letter): On this infinite grid of ideal one-ohm resistors, what's the equivalent resistance between the two marked nodes? ...
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76 votes
20 answers
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Why doesn't current pass through a resistance if there is another path without resistance?

Why doesn't current pass through a resistance if there is another path without resistance? How does it know there is resistance on that path? Some clarification: I understand that some current will ...
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63 votes
6 answers
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In what order would light bulbs in series light up when you close a long circuit?

For a few days, I was thinking of this question. Lets assume we have a simple circuit that is 100 meters long. And lets say that we have bulbs A, B and C connected to the circuit's 30th, 60th and ...
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59 votes
16 answers
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Intuitively, why does putting capacitors in series decrease the equivalent capacitance?

Can someone please explain, intuitively (without any formula, I understand the formulas), why the equivalent capacitance of capacitors in series is less than the any individual capacitor's capacitance?...
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56 votes
7 answers
19k views

Cyclist's electrical tingling under power lines

It's been happening to me for years. I finally decided to ask users who are better with "practical physics" when I was told that my experience – that I am going to describe momentarily – prove that I ...
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52 votes
13 answers
11k views

What *exactly* is electrical current, voltage, and resistance?

I am taking AP Physics right now (I'm a high school student) and we are learning about circuits, current, resistance, voltage, Ohm's Law, etc. I am looking for exact definitions of what current, ...
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48 votes
3 answers
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Why do we use Root Mean Square (RMS) values when talking about AC voltage

What makes it a good idea to use RMS rather than peak values of current and voltage when we talk about or compute with AC signals.
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45 votes
6 answers
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Does alternating current (AC) require a complete circuit?

This popular question about "whether an AC circuit with one end grounded to Earth and the other end grounded to Mars would work (ignoring resistance/inductance of the wire)" was recently asked on the ...
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44 votes
11 answers
11k views

Birds on a wire (again) - how is it that birds feel no current? They are just making a parallel circuit, no?

I have been thinking about this and I know that other people have answered this on here, but there's one part that still baffles me, and it has to do with parallel circuits. If I connect a battery ...
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43 votes
8 answers
179k views

Difference between live and neutral wires

In domestic electrical circuits, there are 3 wires - live, earth and neutral. What is the difference between the live and neutral wires? As there is AC supply, it means that there are no fixed ...
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42 votes
15 answers
101k views

I don't understand what we really mean by voltage drop

This post is my best effort to seek assistance on a topic which is quite vague to me, so that I am struggling to formulate my questions. I hope that someone will be able to figure out what it is I'm ...
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40 votes
9 answers
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If electrons are identical and indistinguishable, how can we say current is the movement of electrons?

When we talk about current, we say electrons are "flowing" through a conductor. But if electrons are identical particles, how does it make sense to talk about them flowing? To expand on that:...
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32 votes
10 answers
7k views

What happens to an inductor if the stored energy does not find a path to discharge?

Suppose an inductor is connected to a source and then the source is disconnected. The inductor will have energy stored in the form of magnetic field. But there is no way/path to ground to discharge ...
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32 votes
5 answers
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When jumping a car battery, why is it better to connect the red/positive cable first?

When jumping a car battery the standard advice is to connect the red (positive) cable first. What's the physics explanation for this?
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31 votes
6 answers
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How can Ohm's law be correct if superconductors have 0 resistivity?

Ohm's law states that the relationship between current ( I ) voltage ( V ) and resistance ( R ) is $$I = \frac{V}{R}$$ However superconductors cause the resistance of a material to go to zero, and ...
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30 votes
7 answers
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Could someone intuitively explain to me Ohm's law?

Could someone intuitively explain to me Ohm's law? I understand what voltage is and how it is the electric potential energy and that it is the integral of the electric field strength etc. I also ...
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30 votes
10 answers
8k views

Is every open circuit a capacitor?

I think that even open-ended wires can let AC current flow through them, just with a low capacitance. I also think an antenna could be a capacitor and open ended. Am I thinking correctly?
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30 votes
10 answers
90k views

Electricity takes the path of least resistance?

Electricity takes the path of least resistance! Is this statement correct? If so, why is it the case? If there are two paths available, and one, for example, has a resistor, why would the current ...
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29 votes
3 answers
5k views

How does energy flow in a circuit? Which is correct?

I have been very interested in this question since reading Electricity Misconceptions by K-6 There are two perspectives I have come across for how energy flows in a circuit: Electrons carry charge. ...
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28 votes
5 answers
5k views

Is there a simple proof that Kirchhoff's circuit laws always provide an exactly complete set of equations?

Suppose I have a complicated electric circuit which is composed exclusively of resistors and voltage and current sources, wired up together in a complicated way. The standard way to solve the circuit (...
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26 votes
5 answers
43k views

How does power consumption vary with the processor frequency in a typical computer? [closed]

I am looking for an estimate on the relationship between the rate of increase of power usage as the frequency of the processor is increased. Any references to findings on this would be helpful.
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26 votes
2 answers
8k views

Resistance between any 2 nodes on an infinite square grid

This question is motivated by this xkcd comic strip . The problem is indeed interesting, and my first recollection upon reading this was a similar problem in the book Problems in General Physics by I....
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25 votes
5 answers
31k views

What's the physical meaning of the imaginary component of impedance?

As you know, impedance is defined as a complex number. Ideal capacitors: $$ \frac {1} {j \omega C} \hspace{0.5 pc} \mathrm{or} \hspace{0.5 pc} \frac {1} {sC} $$ Ideal inductors: $$ j \omega L \...
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24 votes
3 answers
10k views

Why do 'dead' batteries work again after exchanging the places of the batteries in an electronic device?

My camera, which is powered by two AA batteries in series, would not power on. I removed the batteries, exchanged their locations, and the device worked again - for another 15 minutes or so. The ...
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23 votes
6 answers
7k views

Does Ohm's law hold in space?

My current understanding is this: When current passes through a resistor heat is generated which the resistor then gives off to the surrounding air. That way the resistor is kept at roughly the same ...
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23 votes
7 answers
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Are voltages discrete when we zoom in enough?

Voltages are often thought of as continuous physical quantities. I was wondering whether by zooming in a lot, they are discrete. I feel like the answer to the above question is yes as voltages in the ...
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23 votes
8 answers
16k views

Why is capacitance defined as charge divided by voltage?

I understand that capacitance is the ability of a body to store an electrical charge and the formula is $C=\frac{Q}{V}$. What I don't understand, however, is why it is defined as coulomb per volt. Of ...
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23 votes
6 answers
11k views

How do electrons "know" to share their voltage between two resistors?

My physics teacher explained the difference between voltage and current using sandwiches. Each person gets a bag full of sandwiches when they pass through the battery. Current = the number of people ...
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23 votes
5 answers
24k views

Why is there an electric field in a wire even though it is a conductor?

If you take a perfect conductor, there cannot be a field across it since if there were, the particles would arrange themselves in a way to cancel out the field right? Yet, why does the same not hold ...
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22 votes
6 answers
100k views

Will current pass without any resistance?

I've learned that a resistor converts some electrical energy into heat energy while the current flows through it and thus causes a power loss, but what if there's not any resistor in a circuit. Will ...
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22 votes
3 answers
46k views

What happens when we connect a metal wire between the 2 poles of a battery?

As I remembered, at the 2 poles of a battery, positive or negative electric charges are gathered. So there'll be electric field existing inside the battery. This filed is neutralized by the chemical ...
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22 votes
2 answers
6k views

Why doesn't the electric field inside a wire in a circuit fall off with distance from the battery?

We studied electric fields due to point charges. The magnitude of these fields decreases with the square of the distance from the point charge. It seems to me that we could treat the positive ...
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22 votes
5 answers
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Doesn't Veritasium's Recent Video About Circuits Violate The Speed Of Light?

A recent Veritasium video discusses the following circuit: ...
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21 votes
7 answers
4k views

Is the voltage ever undefined?

I was in a question in Electronics SE, and a lot of people said something that I'm sure is wrong. They said, "The voltage between two points that are not part of the same circuit is undefined&...
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21 votes
9 answers
7k views

The water analogy seems to imply that power = current. Why is this incorrect?

Many people think of the water analogy to try to explain how electromagnetic energy is delivered to a device in a circuit. Using that analogy, in a DC circuit, one could imagine the power-consuming ...
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  • 379
21 votes
3 answers
144k views

Different batteries connected in parallel

If we have 2 batteries one of emf x and the other is of emf y and we connect them in series we get an effective emf of x+y. But what if we connect them in parallel, how to calculate the emf now?
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20 votes
6 answers
88k views

In an alternating current, do electrons flow from the source to the device?

If electrons in an alternating current periodically reverse their direction, do they really flow? Won't they always come back to the same position?
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20 votes
4 answers
4k views

Are the "bird sitting on a live wire" answers wrong?

Long ago, my high school teacher wrote the popular question on board, "Why doesn't a bird sitting on a live wire get electrocuted?" He gave us four options (I don't remember all of them) ...
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20 votes
2 answers
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Where does electricity go from a solar panel that is not plugged in to anything?

I found a similar question here on this site, but my question is slightly different. If a solar panel is exposed to sunlight but is not plugged in to anything--dc load, inverter, etc--where does that ...
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19 votes
12 answers
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Why doesn't the voltage increase when batteries are connected in parallel?

Can you please explain the thing below? When we add a battery in circuit then, it gives out some electric field that moves through the circuit and gives a force on electrons in conductor to produce ...
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19 votes
4 answers
4k views

Are the plates of a battery really charged?

In a zinc/copper Daniell cell correct me if I am wrong : Zinc has 2 valence electrons. So it wants to get rid of them. To do so it sends them to the copper which needs 2 to complete its valence shell....
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19 votes
9 answers
18k views

What happens to half of the energy in a circuit with a capacitor?

For a simple circuit with a battery supplying a voltage $V$ to a capacitor, let us assume that the charge on the capacitor is $Q$. Now, the work done by the battery or the energy supplied is given by ...
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19 votes
4 answers
2k views

Distorted colors of Google StreetView photographs near electric power lines

This is a followup to my question: Cyclist's electrical tingling under power lines Some users presented a convincing picture that the electric shocks under power lines are primarily from the ...
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18 votes
5 answers
20k views

Is current in superconductors infinite? If they have 0 resistance then I (V/R) should be infinite? [duplicate]

I learned many years ago that according to Ohm's law, current is equal to voltage divided by resistance. Now if superconductors have zero resistance then the current should be infinite. Moreover the ...
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18 votes
1 answer
2k views

Reduction of Maxwell's equations to classical circuit theory

Can classical circuit theory based on lumped element models be obtained from Maxwell's equations as a limiting case in an appropriate sense? If this is the case, what exactly are all the assumptions ...
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18 votes
9 answers
39k views

Does a current carrying wire produce electric field outside?

In the modern electromagnetism textbooks, electric fields in the presence of stationary currents are assumed to be conservative,$$ \nabla \times E~=~0 ~.$$ Using this we get$$ E_{||}^{\text{out}}~=~E_{...
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18 votes
8 answers
40k views

What is Electromotive force (EMF)? How is it related to potential difference?

What is Electromotive force (EMF)? How is it related to the potential difference? Is it created by the potential difference in any conductor? Is it a process? Why is it called force? Does writing EMF ...
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  • 857
17 votes
6 answers
40k views

Why is current the same in a series circuit?

So I am a 10th grade student and my teacher told me that the current is the same at every point in a series circuit. It does split up in parallel circuit but it then recombines and the current flowing ...
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17 votes
8 answers
392k views

Why do bulbs glow brighter when connected in parallel?

Consider a circuit powered by a battery. If light bulbs are attached in parallel, the current will be divided across all of them. But if the light bulbs are connected in series, the current will be ...
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17 votes
6 answers
13k views

Why does a Resistor cause a potential drop?

I need to know the underlying physics of what exactly happens different with the electric field in the resistor than in superconducting wires. Why is it that when I connect a resistor, potential drops ...
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