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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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2answers
44 views

What causes a magnetic field to be produced at a point in space, when an electric current is flowing nearby?

We know that a current induces a magnetic field along a circular path around it But what exactly causes the magnetic field to produced in that point of space? Is it that change in the direction or ...
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Confusion about Ohm's law

So does ohms law say if the resistance is increased the voltage will also increase but not the current? And in non ohmic conductors the current increases with the voltage even though the resistance is ...
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How does an increase in potential difference increase the resistance of a non-Ohmic conductor?

I am a little confused with the reasoning of why an increase in potential difference (P.D.) increases the resistance of a non-Ohmic conductor, namely a filament lamp. From what I've seen this is the ...
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If the cross-sectional area of a wire doubles shouldn't the current also double?

In this question the answer is B but I don't understand how that could be possible considering the area has doubled.
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Using ammeter to measure voltage

Suppose you have the following circuit: Where R1 = 1 kΩ, R2 = 2 kΩ, R3 = 3 kΩ, R4 = 4 kΩ, R5 = 5 kΩ, Vs = 5V. The voltage in the branch with R5 is then 5 I where I over R5 is .064A. Suppose you ...
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Charge stored in a capacitor with dielectric when relative permittivity varies

Suppose the relative permittivity of the dielectric in an uncharged capacitor of capacitance C varies with the voltage applied, e.g. k=xV where x has dimensions of V^-1 (After this capacitor is given ...
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35 views

Why can two nodes at the same potential be collapsed into one node?

I have a problem where I have a cube with resistance $R$ along each edge. I am asked to find the potential between various nodes (corners) using symmetry and the fact that two nodes at the same ...
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Voltage Change Across a Resistor/Circuit

Say you have a 9 volt battery, and you connect the two ends of the battery with a wire to form a circuit with no resistor. If you measure the potential difference between the two ends of the battery, ...
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A doubt and different approach regarding “A hypothetical magnetic field existing…”

A popular question from the book HC Verma's Concepts of Physics goes like this:- "A hypothetical magnetic field existing in a region is given by $$ \vec{B}=B_{0} \vec{e}_{r} $$ where er denotes the ...
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1answer
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Opacity/transparency of conductive meshes to charged particles (electrons/ions)

When using a conductive (metal) mesh, effectively a metallic woven fabric, in vacuum applications as a "grid" for charged particle optics, how does one calculate (or at least estimate) the opacity or ...
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What causes an electric shock - Current or Voltage?

Though voltage and current are two interdependent physical quantity, I would like to know what gives more "shock" to a person - Voltage or Current? In simple words, will it cause more "electric - ...
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Proof of continuity of voltage across a capacitor

It is known that the voltage drop across a capacitor is a continuous function of time. This means that, for each instant t0, we may write: V(t0-) = V(t0+) This relationship is very used in the time ...
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What happens to the brightness of bulbs if there is a “bridge” with a bulb connecting 2 branches in a parallel circuit? [on hold]

The title might be poorly worded but here is a picture: Bulb A & C is the same, bulbs B & D is the same and bulb E is added to the circuit as shown. What would happen to the current flow/...
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159 views

How to implement the form of current density in a Hall Effect related calculation?

Please consider the following; Question. A rectangular plate of semiconducting material has dimensions 10mm x 4mm x 1mm. A current of 3 mA flows along the length and a Hall Voltage of 13.6 mV is ...
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Confusion in usage of formulae for power dissipated in a circuit

When should we use $\frac {V^2}{R}$ and when to use $I^2R$. Because many times they ask about the power without giving details about series and parallel. I am really confused
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Why does Griffiths's book say that there can be no surface current since this would require an infinite electric field for an incident wave?

In sec. 9.4.2 Griffiths shows the well known boundary conditions for E and B fields, one of them is this: $$\frac{1}{\mu_{1}}\textbf{B}_{1}^{\parallel}-\frac{1}{\mu_{2}}\textbf{B}_{2}^{\parallel}=\...
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Some confusion regarding RLC circuits

I'm a mathematics student, and it has been years since I last did current/voltage/resistor related subjects in high school. However, for one problem that I've encountered, I actually need to calculate ...
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249 views

Long Current-Carrying Solenoid

Why is the magnetic field inside a long current-carrying solenoid does not depend on distance from the axis?
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Stumped on understanding a Feynman lecture about force from wire on magnet

I must (sheepishly) admit that I'm stumped on a beginning page of The Feynman Lectures Volume 2. I have included a picture from the page. [Let me know if I'm breaking copyright, or if I can include ...
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1answer
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Is electricity perpetual in a superconductor system?

I wonder if electricity consumption happen according to the Law of conservation of energy and Joule effect, in a regular circuit certain amount of energy is transformed into heat by components ...
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287 views

Is electric current frame dependent?

I came across a question in which an observer moves parallel to a current carrying wire(say 2A) with drift velocity(in the same direction as electrons) and then it has been asked what will be the ...
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What am I supposed to look for in the question “What is the total resistance between $X$ and $Y$?” [closed]

I'm not really concerned with answering the question but more so what I'm trying to look for. The question is "Three resistors are connected as shown. What is the total resistance between $X$ and $...
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Relation between AC Current and electromagnetic wave in transmission lines?

I m so confused we started by learning about electromagnetic waves in the vacuum , then we went to transmission lines and there the professor mentioned the em waves are traveling through them. I ...
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1answer
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Can any other thing rather than current pass through conductor? [closed]

A conductor is an object or type of material that allows the flow of charge (electrical current) in one or more directions. Materials made of metal are common electrical conductors. Electrical current ...
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Meaning of negative emf in the context of Kirchhoff’s Voltage Law

I’m wondering what it means when the emf of a battery is calculated to be a negative value through Kirchhoff’s Voltage Law. This is the problem: As you can see, we’re given the currents, and we can ...
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Could you transmit electricity wirelessly?

Since you can wiggle an electron to get a radio wave And if you 'wiggle' it fast enough you get higher and higher frequency right? So couldn't you just broadcast an electromagnetic beam or whatever ...
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In a simple resistor circuit, does the current reach V/R instantaneously?

Essentially, if I were to plot current against time for a simple circuit with a DC cell and a resistor in it, would there be a non-flat profile from time $t = 0$. So, between $t = 0$ and $t = t_1$, ...
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Ampere's Law question

If we have a current carrying wire through a rectangular loop, the magnetic field through the loop, according to Ampere's law, is $\int B\,dl=\mu I$. But what if we have a second wire going through ...
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What is the difference between conventional current and electronic current?

what is the difference between conventional current and electronic current? How are they linked to one another?
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Explanation on the current circulation in a circuit

I'm studying the electromagnetsim, and I couldn't find a complete explanation on how the current flows in a circuit; I mean, basically, how do I decide whether the current is flowing in or out a node? ...
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1answer
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Chemistry of electrical conductivity of pure water

I understand the electrical conductivity of pure water is very low, but not zero, and is due to the slight number of H+ and OH- ions naturally present. I understand that they will move under the ...
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1answer
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Relation derivation based on the definition of Current Density

The current density is defined as: $$\textbf{J} (\textbf{r},t) = \rho(\textbf{r},t) \cdot \textbf{v}(\textbf{r},t)$$ where $\rho (\textbf{r},t)$ and $\textbf{v}(\textbf{r},t)$ is the charge density ...
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What does it mean by an AC of Infinite frequency?

For an AC of infinite frequency, Time period= 1/frequency = 1/$\infty\ $ = 0 So, this means the polarity of AC is 'reversed in every 0 seconds'? Can you clarify this phrase?
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Potential difference and current

According to Ohm's law: $V=IR$. Therefore $V$ is directly proportional to $I$. Furthermore, $V=W/q$ and $q=IT$. Thus $V=W/IT$. Therefore $V$ is inversely proportional to $I$. How can $V$ be both ...
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Electric field in a wire

Reading through my lecture notes I have written that the electric field $E$ drives a current $I$ around a wire such that $E = \frac{V}{L}$ where $L$ is the length of the wire and $V$ is the potential ...
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Why is the charge naming convention wrong?

I recently came to know about the Conventional Current vs. Electron Flow issue. Doing some search I found that the reason for this is that Benjamin Franklin made a mistake when naming positive and ...
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3answers
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Current in Square loop under electric field

From "Introduction to Electrodynamics" by David J. Griffiths, Example 12.13: Consider a rectangular loop of wire carrying a steady current $I$. Picture the current as a stream of noninteracting ...
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1answer
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What is the magnetic field of a radially moving current?

Let's say free electrons are contained in a small cloud because of electrostatic forces confining them. Now, if those walls vanish, the cloud will expand very fast because of the coulomb force ...
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Is there something similar to Bernoulli effect with electricity?

There are many parallels between fluid dynamics and electricity. Is there a thing similar to a Bernoulli effect with electricity? For example, would you see a decrease in voltage as the conductor ...
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1answer
295 views

Ohm's law and current due to magnetisation

I'm reading Landau's Electrodynamic of continuous media, specifically the following paragraph of section §29 (The magnetic field of a constant current): If a conductor carries a non-zero total ...
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1answer
20 views

Inductor behaviour in LC oscillation [closed]

I want to ask that in LC oscillation , when the capacitor is discharging then on other side the current is increasing in inductor do inductor should act means it should oppose the current ....as same ...
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3answers
52 views

What happens to resistance if we double current intensity?

problem: what happens to resistance if we double current intensity ? my attempt: ohm's law tells us $R = { V \over I }$ so : $${R \over 2} = { V \over 2I }$$ so resistance should decrease to half ...
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4answers
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Sinusoidal currents in AC circuits

(I had edited this question a number of times but did not receive a satisfactory answer. So I am re-wording this question yet again. The earlier version of this question can be found here : https://...
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3answers
477 views

Relationship Between Conductivity and Lossiness of a material

I read that a material is loss-less if the conductivity is zero. I have always learned that conductivity is a measure of how easily the material can conduct a current. Does this then mean that the ...
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1answer
268 views

If we increase dimensions of a wire, how does electron density change?

If we increase the diameter of a wire, does the electron density change at all? When we increase the diameter or the length of a wire (while solving numericals) do we add appropriate number of ...
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3answers
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Is four-current $J^{\mu}$ necessarily timelike?

In the spacelike case, there is a frame in which the charge density vanishes but current density does not. Additionally, the drift velocity of a free current would propagate superluminally. For this ...
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Skin depth; EM wave and AC

When I google skin depth, I get the following definition, Skin effect is the tendency of an alternating electric current (AC) to become distributed within a conductor such that the current ...
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How current flows in an ideal wire when there is no potential difference? [duplicate]

Such as in this case: Even though potential difference between points A and B is zero, a current of 9A will flow between these two points. Why it is so? I understand potential difference must exist ...
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2answers
332 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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1answer
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Paradox on setting up charges on capacitors

Staring with facts, 1)For a current to flow there must be a closed loop. 2)For a capacitor to be charged there must be a potential difference across it, 3)And obviously a charge must be transferred ...