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
120 views

Does current flow when you connect a battery to earth?

Let's say that the earth has 0V and everything is ideal, does current still flow and why?
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1answer
69 views

Are these two circuit equivalent? [closed]

are the two circuits equvalent ? I have actually got a different problem (wheatstone bridge) but,I want to make sure that there is no mistake in my assumption before asking that question. In the ...
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2answers
89 views

Doubt about current density [closed]

We are taught in electrodynamics classes that current density is a vector quantity while current is a scalar. I understand why current is a scalar and current density is a vector. But what's troubling ...
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2answers
65 views

Potential difference of resistors in parallel linked systems

Before the question I want to explain somethings to see if I understand anything wrong please tell me if im wrong: When there is a Potential difference on a system then the electrical charge will move ...
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1answer
39 views

Will there be an induced EMF if the windings have no resistance?

Imagine a transformer, the primary has a voltage source, a 5 Ohms resistor, and obviously the windings too. If there were no resistance on the windings will there be any emf induced on the secondary ...
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1answer
96 views

Can electric potential be discontinuous?

I am studying the following problem, which is 9.11 of "Modern Electrodynamics" by Zangwill. The idea is that you have a wire attached to a perfectly conducting sphere (radius $a$) buried into the ...
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2answers
64 views

Is it the current which create magnetic field, or vice versa, or both?

Talking about stationary magnetic field, it is said that if a conductor rotates inside the field, a current is induced. Also, I read that current (moving charges) generate magnetic field, too. How are ...
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What were the 3 crirical experiments and the argument given by Ampere which helped in determining the magnetic field made by electric current?

In The Feynman Lectures on Physics volume 2, Magnetostatics, section 13-4 Mr. Feynman tells us that there were "three critical experiments and a brilliant theoretical argument given by Ampère" that ...
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1answer
89 views

The flow of electric current

If positive charges have higher electric potential difference than negative charges then why the negative charges (electrons) are the one that are moving in a circuit? and to my knowledge the ...
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4answers
107 views

Should a Step Up transformer necessarily need more Windings?

The Primary & Secondary has the same number of coils/windings, but the resistors on them are different, using P=I2 × R, we get that the current in the Secondary side decreases and Voltage ...
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4answers
121 views

How to understand Kirchhoff's Voltage Law?

I'm having a hard time trying to understand why Kirchhoff's Voltage Law is true. I looked for an answer on the forum but I couldn't find a convincing one. So my question is : How to "physically" ...
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1answer
161 views

Why is a parallel RLC circuit usually driven by a current source?

Almost always when I see an example of a parallel RLC/LC circuit diagram online, the circuit is driven by a current source instead of a voltage source. On the other hand, the series RLC is always ...
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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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3answers
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Is electric current relative?

Motion as we know is relative. According to this current which is the flow of charges should be also relative . That means that if someone is moving with the same velocity with repsect to the velocity ...
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1answer
37 views

Can we use magnetic flux formula $BA$ for straight wire/conductor placed in uniform magnetic field

While coming across electromagnetic induction, I learned that for an emf to be induced in a coil of wire there should be a change in magnetic flux which is given by $\frac{BA\cos\theta}{t}$ where ...
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4answers
110 views

Why Voltage Increases in a step up Transformer rather than the Current?

In a step up transformer, we all know voltage increases and current decreases, the answer to more voltage is because it has more windings, but why does more windings induce more voltage, can't the ...
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1answer
76 views

Measuring the earth's electric field

My question stems from a question on the Dutch VWO-level highschool state exam (from 1993) concerning a device to measure the earth's electric field. It consists of two plates positioned above one ...
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35 views

Would there be any current if an electric circuit is cooled to absolute zero?

My question is if I got a superconductor and cool it to absolute zero at least measurable by today's tool, it should have no electrical resistance but then would there be any current when there is a ...
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1answer
230 views

Does Kirchhoff's Law always hold?

There's a bit of furore from this question on Youtube involving Dr. Walter Lewin and another Youtuber. With Dr. Lewin claiming Kirchhoff's Law doesn't always hold when magnetic fields are involved, ...
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2answers
38 views

Voltage across parallel resistances

A resistor is connected to a battery of certain potential difference, it has now $V$ volt potential difference across its ends, after some time a resistor is connected in parallel with it. How does ...
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2answers
61 views

What is the voltage in electrical circuits?

I understand what the voltage is and I realize that the battery makes an electric field due to the accumulation of the charges in the anode and cathode this electric field causes electric potential ...
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2answers
30 views

Is voltage basically the measure of the strength (or density) of an electromagnetic field? And does an increase in voltage increase the amperage?

I have been in the process of fully understanding what is generally accepted as truth by the scientific community regarding voltage, watts, and amperage. Most engineers seem to say to simply use the ...
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1answer
31 views

Is there a limit on the magnetic field in a Hall generator?

In a Hall generator, charge accumulation on electrodes occurs because there is a generated current, $\bf{J}$, in a magnetic field, $\bf{B}$. This results in charge separation due to a Hall current ...
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2answers
159 views

Magnetic field in Ohm's law

In a linear, stationary, isotropic, homogeneous, only time-dispersive medium one usually writes Ohm's law as: $$\underline{\mathcal{J}}(\underline{r},\omega)=\sigma(\omega) \underline{\mathcal{E}}(\...
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1answer
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Conceptual question on volume current density and derivation of the continuity equation

The expression for the volume integral of the volume charge density is $\int_{V} (\nabla \cdot\vec{J}) d\tau = -\frac{d}{dt} \int_{V} \rho d\tau = -\int_{V} (\frac{\partial \rho}{\partial t}) d\tau$...
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1answer
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What is the EMF in a bar rotating around any point?

The problem of a bar (or rod) of length $l$ rotating around one of its ends in a magnetic field of magnitude $B$ is very well known. The induced emf is $\frac{1}{2}B\omega l^2$, where $\omega$ is the ...
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4answers
71 views

Can Induced current be obtained by only changing the direction of the Magnetic Field?

According to Faraday, a change in magnetic flux induces current in a conductor. Just suppose we take a circular coil, and pass a magnetic field inside it, and keeping changing the direction of ...
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40 views

How a battery maintains the current in the circuit? [duplicate]

How a battery maintains the current in the citcuit? Iwant to know each and every step of this process mathematically and theoretically also.
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5answers
5k views

Why does a 60W bulb glow brighter than a 100W bulb in a series?

In my physics class I have this problem that shows two lightbulbs, one 60W and one 100W in series, connected to a 120V battery. The problems are: Which bulb is brighter? (A: 60W) Calculate the ...
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8answers
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Understanding voltage and power in the fluid analogy for DC circuits

I am trying to understand electric circuits (ie voltage, current, power, and resistance). For the most part, everything makes perfect sense, but for some reason I do not feel as if I understand the ...
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1answer
42 views

Movement of electrons in a circuit

Electrons move from negative to a positive terminal, but their path seems unusual. They seem to be taking the longer path to get to the positive terminal, The electrons could have gotten closer to ...
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1answer
55 views

Magnetic Force on a current carrying conductor

Why does a current carrying conductor parallel to the magnetic field not experience a force?
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0answers
64 views

How to calculate the current generated by a thin film?

I have a thin film with known dimensions and conductivity. If I hook up wires and apply a bias, how can I calculate/estimate the current that I will get? Here is where I'm at: $$ \mathbf{J}=\sigma \...
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What's the reason behind the current remaining the same after passing by a resistance?

I've been wondering why does this really happen, I mean by intuition if electrons are driven by EMF (ignoring wire's resistance), $n$ coulombs would pass by a point per second, until they encounter ...
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Why doesn't current flow between the wires in a coil?

Didn't find the answer online, maybe because of bad searching. So hope you here can give me an explanation. In an engine or transformer the coil is tightly wired, but how come the current doesn't ...
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1answer
271 views

Surface current density confusion

From Griffiths' Intro to electrodynamics: Now I'm confused about 3 things: 1) What is the 'mobile' surface charge density? Isn't the surface current density itself the 'mobile' surface charge ...
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1answer
23 views

How to explain these observations on the first load, with two loads in series?

Recently I purchased the Snap Circuits Jr. kit and was working through the different projects with my daughter. We decided to connect two loads in series circuit, powered by the battery source. The ...
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1answer
312 views

Ampere's Circuital law proof for closed circular loop

How do we prove the magnetic field for a circular loop is $\frac{\mu_0I}{2r}$ using Ampere's Circuital law I proved it using Biot-Savart Law but i am getting $\mu_0I/2\pi r$ instead of $\frac{\mu_0I}{...
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How is current in superconductors increased microscopically?

Imagine a superconductive ring with its current being increased by EM induction. How is current increased microscopically? I see only two possibilities: ...
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0answers
38 views

What is the electrical resistivity of air during breakdown?

There is a well-documented theory for breakdown voltage vs pressure in the form of Paschen's law. But what is the trend of the electrical resistivity of air as a function of the electric field ...
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Proof that true passive linear memristors don't exist

This is a sequel to the following (now irrelevent) question: My attempt to implement linear memristor Assume the "conceptual symmetry" of the fundamental passive circuit elements holds: Then let's ...
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COMSOL magnetic field time dependent [closed]

enter image description here I need to modelling conductor in Comsol 5.3 by MF physics in Time Dependent study Conductor model "Single conductor" in "Coil" feature doesn't work in TD study, and ...
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3answers
445 views

Does touching the Live wire makes it neutral?

If I have two 'hot' wires connected to a source and a load, and one of the wire is connected to the ground, this wire is called the 'Neutral'. But what happens if instead of using an additional wire ...
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2answers
34 views

Why doesn't ionized air give you a current shock?

According to Tesla coil, the air gets ionized and why doesn't ionized air give current shock to a person standing in the ionized air?
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1answer
48 views

Conservation of bound charge? [closed]

It is intuitively obvious that free charge is conserved in vaccum. But when is bound charge conserved? I tried to find this by formula: The charge conservation law in microscopic view (Assuming there ...
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2answers
110 views

In superconductivity, does the diameter of the cable affect the current?

In the water tank analogy below, the smaller diameter pipe (B2) will drain tank A slower than the larger diameter pipe (B1) We are told that resistance has this same effect on current the bigger the ...
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1answer
38 views

How do I experimentally measure the resistance from using dielectric grease on battery posts?

The internet gives lots of contradicting advise about greasing or not greasing car battery posts to prevent corrosion. So rather than rely on the internet, I want to perform an experiment so that I ...
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2answers
75 views

Touching single line of AC Power and charge oscillation in body

If a person touches a single line of AC(Only on the live line, and no where else. Say he/she is hanging on the power line using one hand) as shown in the attached image, Do the ions in his/her body ...
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2answers
68 views

Why is the electric potential difference independent of resistance?

According to wikipedia the definition of electric potential difference is as follows: The difference in electric potential between two points (i.e., voltage) is defined as the work needed per unit ...
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1answer
218 views

Charge accumulation in wire

I came across a question about charge accumulation. It states that if a steady current flows in a wire composed of a copper and iron wire of same area (see fig), will the charge accumulate on the ...