# Questions tagged [electric-current]

A measure of the rate at which electric charge is transported (especially through a circuit), it has units of charge/time.

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### Current due to physically rotating a charged hoop — Is there emf associated? How is the scenario analyzed in electromagnetism?

Suppose I have a conductive metal hoop with insulator spokes that attach to a fixed gear. Now suppose I provide positive charge to the metal hoop and then I physically give it angular momentum. (For ...
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### How electrolytes conducts electricity?

While studying electrochemistry, I came across two key points that I'm unable to understand. why does DC alone break down the electrolytic liquid and b) Why doesn't AC do the same?
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### Electrical resistance of wet wood with voltage [closed]

in recent science projects I have been studying the effect of water on electrical resistance of materials that absorb water such as wood and sponge. I am calculating resistance by reading the current ...
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### Understanding if possibly current density can be made scalar by changing the current definition?

In the accepted answer to this question : Why does current density have a direction and not current? I understand the need for current density to be vector, but I am now curious if the definition of ...
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### Is $V_\text{RMS}$ an unfortunate abuse of operator?

My book introduces RMS voltage as typical in a discussion regarding AC circuits, however I now understand this as a tool of statistical mechanics. It would seem as though oscillation is not a great ...
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### Understanding the sources for the contributions made for the presence of electric field inside and outside the current flowing conductor

Consider a setup of a battery with a current carrying conductor. There are three contributions to electric field outside and inside of the wire that is by. surface charges on the conductive wire by ...
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### Understanding the role played by moving charge in electric field and why charges reside on surface only in current flowing conductor too

Suppose a direct current is flowing in a long straight conductor , in the comment below the answer in this link https://physics.stackexchange.com/a/62166/312538 by Ján Lalinský its being said that ...
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### THÉVENIN Equivalent of Circuit [closed]

I tried to convert the right generator of, current and resistance, to a generator of voltage in series with the resistances then adding the two resistances (both in series), then simplifying, but I ...
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### Inductor connected to an AC source

Consider an inductor connected to an AC source, $V=V_0\sin\omega t$. Let the the switch in the circuit be closed at $t=0$. Then by Kirchoff's voltage law, $$V-L\frac{dI}{dt}=0$$ where $I$ is the ...
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### Find the external work for getting the wire from $\infty$ to the current location. (the potential in $\infty$ is $0$)

A ball of radius $R$, with charge density: $$\rho(r)=\beta r,\quad\beta > 0$$ A thin wire, with charge density: $\lambda[\frac{c}{m}]$ and length $R$, located between $x=2R$ and $x=3R$. My ...
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### Why Do Van De Graaff Generators Only Shock When Grounding Someone?

When someone touchs the metal sphere of the Van De Graaff Generators, the charge on them builds up, causing the famous hair raising. However, why is it when a person is rapidly grounded by someone ...
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### Is there any material available whose strength changes with an input stimulus, say current or magnetic field etc?

Is there any material available whose strength can be controlled by varying an input stimulus like current flowing through the material or magnetic field without actually deteriorating the material ...
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### Kirchhoff's voltage law, signs?

Consider the circuit below from the book Electrical Engineering, Principles and Applications (p. 95). According to that book, we get from Kirchhoff's voltage law that $$-v_1+0.5v_x+v_2=0$$ However, ...
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### Is AC current equation in an RC Circuit wrong? [duplicate]

This is about the RC circuit current equation in AC which is similar to and RL circuit and both these equation seem to have the same problem. The equation is I=(V0/Xc)sin(wt+90) where I is the ...
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### How to correctly measure critical current density in superconductors?

In my experiments, I measure the critical currents of superconductors, and by dividing them by the cross-section areas, I derive the critical current densities. I've also seen colleagues doing the ...
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### Arbitrariness of Quantum Heat Current

Given a Hamiltonian $H$ for a closed quantum system, we know that the spectrum is invariant under any constant shift in energy $H'=H+c$. However, when talking about open quantum system where the ...
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### Two permanent magnets are allowed to attract each other. The field energy MUST decrease as they speed up. But Griffiths implies it INCREASES. How?

This is a relatively long question however I think I hit on a fundamental issue regarding the conservation of energy during magnetic attraction and how it is taught in standard texts. I'd really ...
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### Why is current finite for point charges?

If an electron passes through a flat plane, then there will only be a single point in its entire path which lies on the plane,i.e the entire charge of an electron passes through in an instant (as it ...
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### Current sign convention RC and LC circuits

When deriving the equations for RC and LC circuits we substitute the current in the circuit with the time derivative of the charge on the capacitor. However, when I think about it, the rate at which ...
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### How Can we Verify Mathematically, that electric field inside a current carrying conductor have same magnitude?

So, I was revising my concepts of Current and electricity,and while watching a related video on youtube, I came accross this video.... A simpler representation of above circuit is shown below-- NOTE:...
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### Actually my thought got stuck into a very curious question that what happen if we pass 1electron charge through a parallel combination of resistors? [closed]

Idea of conservation of charge ;division of charge in parallel combination ;smallest magnitude of charge that is of 1electron charge.and somewhat imagination.
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### Can changing magnetic field make a ferromagnetic material into a paramagnetic material

Suppose a ferromagnetic material (iron bar) is placed inside a solenoid that produces a sufficiently high changing magnetic field (due to AC current). In this case, will the iron bar will become ...
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### On the working of radios and interference of waves driving radios and TVs?

It's a well known fact that radios work by ensuring that the resonant frequency of their LCR circuits matches the frequency of the station one is trying to tune into, however, waves also interfere, so ...
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### How exactly is the value of DC in an AC circuit, given by the RMS of the AC

How and WHY does the RMS of current gve us the equivalent DC? I've been though this answer here:-root mean square for dc but it doesn't answer my question.
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### Circuit resembling wheatstone bridge but not exactly [closed]

The below circuit resembles that of two individual wheatstone bridge arrangements as the ratio of resistances satisfy the conditions however we cannot come to this conclusion as potential at one end ...
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### What happens to resistance of tap water as voltage is increased?

In recent days I have done a few experiments measuring the current of water as it goes up from 9 volts up to 36 volts, and following Ohms law to convert it to resistance. And I discovered a very ...
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### What is the current going into a resistor-capacitor parallel circuit and the current coming out of it? [closed]

I'm looking at the circuit below and know that I1 = I2. Can someone explain why those 2 currents are the same?
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### Why do we represent A/C currents with sine waves?

Why is it harmonic in nature? I am starting to learn about alternating currents and somehow I can’t get the fact that it’s described by a sine wave and not by any complicated waveform. Is there a ...
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### Apparent violation of Gauss Law

Consider the very long, current-carrying wire in the picture. On the left side in yellow, the wire has a very low resistance, that we will consider to be zero. But on the right hand side in green, the ...
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### How to understand electron drift velocity?

I know that electron drift velocity can be defined as $I$ = $nAve$, where $I$ is the electric current, $A$ is the cross-sectional area of a conductor, $v$ is the electron drift velocity in question, ...
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### Steady surface and line current conditions

I know the conditions for a volume current to be steady. My question is how can I know if a surface or line current is steady? + Does the surface current have to have the same surface current density ...
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### Flow of Electrons in Potential divider circuit

Take the above circuit. I'm trying to understand how current flows through this potential divider circuit. I used the following simulation to help me visualize this. In the simulation the electrons ...
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### Derivation of drift velocity treating electrons as doing work on the surroundings as a gas enclosed in a container [closed]

So, the original derivation of drift velocity can be found in this link; Method of averaging velocities of electron when deriving drift velocity Now I used(tried to use, to be more precise) an ...
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### Potential divider problem [closed]

What does the curved arrow represent? The answer states that L1 will be dimmer than L2. From my current knowledge, moving the contact K closer to X will somehow increase the voltage of L2 meaning it ...
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### Phototcurrent illuminated gold plate

Let's say we have a gold plate connected to a current meter and illuminate the plate. How would you calculate the photo current? My first idea was to check the ionization energy of gold $E_{ion}$ and ...
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### Why is it easier to raise AC current to high voltage than DC?

In my country (and maybe all around the world I don't know) once electricity has been generated, it is then raised to 200k Volts for transportation. I know this is to reduce the loss. Given $P=U.I$ ...
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### Voltmeter connected to parallel circuit

This is my current understanding. Voltage is defined to be the potential difference between 2 points, hence it only makes sense for a voltmeter to be connected in parallel. But why must this voltmeter ...
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### Will charge accelerate if we apply voltage accross superconductor? [closed]

Will charge accelerate if we apply voltage accross superconductor
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### Why do we take electric field inside resistor constant? [closed]

Why do we take electric field inside resistor constant
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### A question regarding determining internal resistance of a cell by using a potentiometer

In the given figure at null point J current does not flow through JD and AC but current does flow in the second circuit CDEF and primary circuit.My question is why doesn't current flow through ACFED ...
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### Voltmeter in parallel

I can't seem to understand the problem with connecting a voltmeter in series. All explanations say that voltmeters have extremely high resistance so connecting it in series will effectively stop the ...
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### Anomalous Hall Conductance by Kubo-Greenwood Formula

The Kubo formula is written below. \sigma_{ij}=\frac{e^2}{\hbar}\int_{BZ}\frac{dk_idk_j}{\left(2\pi\right)^2}\frac{1}{e^{\frac{\epsilon_n-\epsilon_{fermi}}{k_BT}}+1}\sum_{n^{'}\neq n}\frac{2Im\...
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### Some things I can't understand about Ohm's Law [closed]

I can't understand how PD is directly proportional to resistance and current intensity at the same time, although they are inverse, I know that an increasing in PE leads to an increase in current ...
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### Find the strongest point of the magnetic field from three long conducting wires

Consider three long power lines buried in the ocean, with (from left to right) current $\frac{I}{2}, I, \frac{I}{2}$, where the direction of the current in the edge cables are negative $z$ (in to the ...
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### Electrostatic attraction between charges in different media

Imagine you have two non-conducting spheres of density a (a < density of water). Therefore the spheres float on the surface of water with a portion of their bodies immersed in water. Now how do you ...
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### Can Chiral symmetry violating term in lagrangian violate charge conversation?

The regular Lagrangian is $\mathcal{L}=\bar{\psi}(i\gamma^\mu\partial_\mu-m)\psi$ If we add a chiral violating term $\mathcal{L}=\bar{\psi}(i\gamma^\mu\partial_\mu-me^{i\theta\gamma^5})\psi$ For the ...
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### Transformers in Power transmission [duplicate]

Recently I learnt that transformers are used in the national grid to increase the voltage, so we get less current. But my understanding V=IR and by increasing the voltage we get more current, so what ...
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### Does this situation violate Newton's third law? How? [duplicate]

Consider the following setup: We have an infinitely long current carrying wire placed on the X-axis. At some 'x' distance from it is another current carrying wire of length l and it is perpendicular ...