Questions tagged [electric-circuits]

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

579 questions with no upvoted or accepted answers
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Express Laplace transform of voltage across a capacitor in terms of charge

In Charge Tunneling Rates in Ultrasmall Junctions section 2.1, the authors consider the problem of charge relaxation in a simple circuit shown in Figure A. The implicitly use an assumption made about ...
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1answer
518 views

How uniquely determined is the impedance of an infinite-chain circuit?

A recent question asked how to find the impedance of an infinite chain of series-plus-parallel circuits. The standard trick is to split the chain after the first link, and treat the tail of the ...
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The origin of contact noise?

I was trying to measure the noise of a device with metal probes. I was not sure whether I should trust the results because I was told contact noise might contribute to some degree. I am a little ...
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4answers
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Temperature distribution in a current carrying conductor

A rod of uniform cross section and composition is connected across a battery. Let the middle part of the rod(when divided into three equal parts) is heated uniformly. A book says that the temperature ...
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0answers
79 views

Formulate the equations that describe this transmission-line circuit (Veritasium's circuit)

My question Consider the following circuit. Two non-resistive long transmission lines ($R' = G' = 0 \text{ } \Omega$) , each of the same length $L$ and same inductance per unit length $L'$ and same ...
4
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1answer
81 views

What does the term 'high voltage' really mean?

This might be a dumb question but i am not so familiar with the word voltage: What does the textbooks really mean when they say high voltage?. Does that mean: There are more charges so more voltage, ...
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Can the Hall effect drive a current?

In the Hall Effect current is passed through a wide strip of metal in a perpendicular magnetic field. Since (some of) the negative charges in the metal move but the positive ones stay put, the ...
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2answers
633 views

What is capacitance, in general?

In circuit analysis software capacitance can be measured between any two nodes of a circuit or of a multiterminal device. In practical terms we take $C_{ij}$, the capacitance between $i$ and $j$ as ...
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1answer
97 views

Salt and electricity

Recently, I did an experiment with salt and electric current. I set up an open electric current in a used battery holder where the missing part of the circuit is two metal plates. I then fill this ...
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1answer
105 views

Apparent paradox of current through two parallel plate capacitors in series in an open circuit

This apparent paradox has been wrecking my brain. Suppose we charge up two parallel plate capacitors (with distance $d$ between each pair of plates) independently with different batteries to voltage $...
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2answers
50 views

Why is there an electric potential drop in electric circuits?

I know a battery creates a potential difference, making an electric field that exerts a force on the electrons, who start moving. But why is there a potential drop after a resistor for example? How ...
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Johnson Nyquist noise with voltage driving

In his 1928 paper, Nyquist derives the famous Johnson-Nyquist noise relation which is, to be very precise according to his paper: It gives the variance of the voltage at the boundary of a resistor ...
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0answers
67 views

Studying Chaos in RLD circuit

We are currently working on non-linear dynamics (chaos theory) by analysing a series circuit including a diode (the 1N4004), a 100 ohm resistor and a 20 mH inductance. It is driven by an alternative ...
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1answer
125 views

Voltage drop in Drude's model and the electromotive force

I'm trying to understand the meaning of the voltage drop and of the electromotive force in view of Drude's model. This model assumes a drift speed for electron equal to: $\mathbf{v_d} = \frac {-e \...
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0answers
79 views

Chua's Circuit: an inequality ensuring that the equilibrium is not stable

According to Kennedy's Robust op-amp realization of Chua's circuit(1992), the differential equations satisfied by several physical quantities in Chua's circuit are $$\begin{aligned} C_{1} \frac{d v_{...
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1answer
189 views

Thermoelectric voltage over a solder joint of two identic copper wires

My background: I'm engineer of electronic HW engineering and embedded computer systems. During repair of a vintage digital voltmeter (resulution 1µV) I discovered an effect that probably only a ...
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2answers
632 views

Flux linkage of 2 coils in series

I have a question about magnetic circuits. I am an engineering student, therefore I will neglect some minor errors. There is a simple magnetic circuit with 2 coils ($C_1$ & $C_2$), with $N_1$ &...
3
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1answer
638 views

Johnson-Nyquist noise for resistive element with temperature gradient

In Nyquist's 1928 paper, Thermal agitation of electric charge in conductors, the voltage noise for a resistor is derived assuming a circuit in thermal equilibrium and one temperature. How does the ...
3
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3answers
360 views

Is brightness proportional to power?

In an exam, I am given a situation where a student investigates how the current varies with potential difference for two bulbs of the same type. For the same voltage, the current of bulb A is twice ...
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7answers
118 views

How can current flow without voltage?

The following is an image from my school textbook How do electrons travel from E to F is voltage (or the J per C of charge) is zero? I think my issue is a deeper misunderstanding of the nature of ...
2
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3answers
49 views

Deriving the equivalent capacitance in a series circuit formula

When we derive the formula for the effective capacitance in series, we say: $$Q/C_{eqv} = Q/C_1 + Q/C_2 + Q/C_3$$ (if there were 3 capacitors in this case). We would then cancel $Q$ to obtain the ...
2
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1answer
104 views

(Too?) simple model of pn junction

I am trying to build a simple model of a pn junction in order to show high school students how it works. I am not looking for something precise, so I use really simple discretization and I discard ...
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0answers
59 views

Why did the defected bulb glow brighter when switched off?

Suddenly an LED bulb in my house stopped glowing (actually it was having very little brightness (can be noticed in the video)). But when I switched off the bulb , it first glows brighter and then ...
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Tilted metallic plate touching two capacitor plates

A parallel plate capacitor of capacitance $C$ is as shown. A thin metal plate A is placed between the plates of the given capacitor in such a way that its edges touch the two plates as shown. Find the ...
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Why did a lack of electrical power generated in Texas recently almost cause fires?

This may be more of an engineering problem... A recent newspaper article stated that the rolling blackouts instituted during the recent cold snap in Texas narrowly averted parts of their grid catching ...
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0answers
101 views

How is the rotational energy of a black hole converted into a magnetic field used to power relativistic jets?

When an electric charge is lowered into a nonrotating black hole it will "spread" itself across the surface, and the surface will behave like an electrical conductor. Why does this spread ...
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0answers
27 views

Does a power station directly control the supplied power or voltage?

The electric grid's "job" is to provide to the end user a steady sinusoidal A/C voltage with an RMS value of 120 V and a frequency of 60 Hz. (That's in the United States - other countries ...
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0answers
25 views

Fermi-Dirac statistics and electrical filter

The graph of Fermi-Dirac distribution near absolute zero and an electrical filter looks very similar. My question is does: this similarity finds any application? I can't think of any scenario as such: ...
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2answers
232 views

Electric field in a DC circuit

I have a power source connected to a resistor in series. I am asked, "what is the electromagnetic field in the circuit?" I know there is a magnetic field due to the moving current but is ...
2
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0answers
118 views

In an $RC$ Circuit, when polarity of a battery is reversed, how much energy is dissipated into heat?

https://ibb.co/tPL02dZ In the figure, a $ 20 nF $ capacitor is connected in parallel across a $ 30 nF $ capacitor. There are $2 $ resistors of $10 Ω$ connected in series with the capacitors. A ...
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0answers
59 views

Circuit quantization and energy dissipation

So when we do the procedure of circuit quantization we use the hamiltonian formalism which is only true when theres no dissipation. however we know real life circuits are dissipative , Im aware that ...
2
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0answers
49 views

How do you apply "flux-rule" in free space?

Faraday's law of induction states that, the tangential component of the force per unit charge$^*$; EMF produced in a loop of wire, is equal to change in the magnetic flux through the loop, $$\int_C \...
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22 views

Photovoltaic Device and Photon Absorption

When dealing with a photodiode photons with lower energy (such as red light) penetrate deeper then a photon with higher energy (such as blue light). The responsivity of the photodiode has a lower ...
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0answers
214 views

In series RLC circuit, does decreasing the capacitance value really make the circuit more capacitive circuit?

This seems very counter intuitive to me. How can decreasing the capacitance value make the circuit more capacitive ? The math tells me so : If $C$ decreases then $X_c = \dfrac{1}{\omega C}$ ...
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364 views

What is Capacitance for a Spherical Shell pair?

Consider three Scenarios : 1) In this case , we are Calculating $$\frac{d(Q_b)}{d( \triangle Vab)} $$ 2) In this case , we are Calculating $$\frac{d(Q_a)}{d( \triangle Vab)}$$ 3) In this ...
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409 views

Approximating the equivalent resistance of a large resistor network

Per the elegant solution of this Phys.SE question we can find the equivalent resistance between nodes $k$ and $l$ of a resistor network like this: $$R_{kl} = {{\rm det}A^{(kl)} \over {\rm det} A^{(l)}...
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80 views

What if in potentiometer, the loops are not balanced to cancel the potential and current flows?

As described in the book (image) that loops should be balanced with equal potential with help of the galvanometer. What if the we do not balance it to zero and have some current flowing? Can we still ...
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1answer
132 views

Tangential Current of plates in charging capacitor (Function of x)

Suppose we have a capacitor which is charging with applied voltage $(V(t)).$ I want to know what the surface current is which is shown in figure. I know the continuity equation says the current of ...
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574 views

Sensitivity of Wheatstone bridge

I was going through my textbook and it told me that the sensitivity of a metre bridge is maximum when the resistances in its arms are equal (at balanced conditions) and for a potentiometer if the ...
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0answers
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What is the most critical aspect of a CDU's output in order to obtain load discharge?

I am trying to better understand the exact circuitry and physics that go into a functioning CDU. Currently, I understand that CDU’s, also known as Electronic Detonator Units (EDU’s) consist of ...
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1answer
36 views

With the help of a given charge is it possible to obtain a charge many times greater in magnitude

Consider a spherically conducting sphere. If a charge(say positive) is placed near the sphere, then it will lead to separation of charges inside the sphere.My question is, can we create charges more ...
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2answers
893 views

What happens to the resistance, voltage and current when DC passes through saltwater?

I have a circuit of a battery(1.5V or 9V) connected to a multimeter, a connected to 2 metal pieces in water(distilled)(see picture, in place of the LED is a multimeter). With the addition of salt 1. ...
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0answers
91 views

Why is the current measured through a thin film increasing with time? (experimental question)

I'm doing an experiment: I'm thermally evaporating a metal in a vacuum onto a quartz (very insulating) substrate, between two gold contacts that I use to measure the current through the (growing) film....
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Concepts in Gabriel Kron's later papers

Gabriel Kron was an important research electrical engineer known for applying differential geometry and algebraic topology to the study of electrical system. Towards the end of his career he published ...
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1answer
34 views

Current in a diode circuit without a external voltage source

Will there be any current in the given circuit? If current exists then why do they exist and what will be the forward and reverse current and voltage(across the diode)?
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25 views

Capacitance of a thin conducting ring

I am following an exercise in which the capacitance of a thin ring is computed. The ring has radius $b$ and thickness $2a$ where $a<<b$. In this exercise they compute the potential due to a ...
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2answers
60 views

Does a higher voltage always mean a higher electric field strength?

In a step-up transformer, the output voltage is higher than the input voltage, while the output current is lower than the input current. Basically, since P = VI is conserved, the current has to ...
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5answers
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Please help understand Electric Potential Loss in a DC circuit

What is meant by "Electrons lose potential Energy" when going through a resistor. In a case of falling from a height you would be at a lower altitude and therefore lower potential but how is ...
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0answers
22 views

Meaning of Continuous Charge in the Inductively Shunted Cooper Pair Box

I asked this question on QC.stackexchange before, but received no answers and only the advise to post ist here. Thus: In the Cooper Pair box, the conjugate momentum $\hat{n}$ of the reduced ...
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1answer
29 views

Time-reversal in a simple current loop

In classical physics, time and velocity change sign under time-reversal while position, acceleration and force do not. An accelerating particle going to the right becomes a decelerating particle going ...

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