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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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Two types of electric field

My textbook mentions that electric field produced by electric charge and that produced by changing magnetic field are different in nature. After searching from various sources I found that electric ...
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2answers
59 views

How can AC current pass through an open circuit?

I think for example for oscilloscope what gets signal just in one wire and how can even ac go through only one wire?
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41 views

Relativistic effect in a current carrying wire

In many places I read that in the rest frame of a current carrying wire (electrons in motion), the spacing between the positive ions is length contracted and equal to the length contracted spacing ...
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41 views

What do $I_{x2}$ and $I_{x3}$ represent in this Circuit? [on hold]

I thought it would be Ix2 = I2 or Ix2 = 2I2. if that makes sense. The question asks for Voltage across R2 but i dont want an answer, i just need to know what those two symbols stand for so i can get ...
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'Why don't electrons accelerate in a circuit' Confusion

https://physics.stackexchange.com/a/18806 Apparently he said 'at the same time', so when the electrons are 'pushed' by the electric field it is 'blocked' by the resistance simultaneously, if he said ...
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0answers
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Difference in Electric conductivity based on connection type?

Is there a difference in electrical conductivity dipending on the way the Material is connected? For example, is there a difference between a copper wire connected to another one „via soldering“, ...
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3answers
70 views

Why doesn't the flow electrons occur in a broken circuit?

Take a battery and connect a small led bulb across it with the help of two wires. The bulb will glow, but if I cut a small piece of wire from any part of the connecting wires,the circuit will not work ...
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2answers
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Why is there no current induced when the coil is vertical in an AC generator?

In this picture, the movement of the coil inside an AC generator is shown. My question is when the angle is zero or like in the beginning, the coil is vertical to the magnetic field yet no emf is ...
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Why is a specific voltage limit needed to light a bulb in an electric circuit

The battery provides a potential difference between its terminals that allow acceleration of the electrons in the circuit, i.e the potential energy gets converted to kinetic energy, these electrons ...
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Secondary current in a loosely coupled transformer

How does the secondary current depend on the resistive load placed on the secondary winding of a loosely coupled transformer, in which the primary winding is supplied with a linear current ramp ?
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0answers
35 views

Why don't rectifiers deplete the AC source of electrons? [on hold]

As I understand it, the most simple rectifier can be made by attaching a diode to an AC source, only allowing half the wave form through, and then adding a capacitor to smooth it out. Then, the end of ...
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1answer
32 views

Which law is true at the transformator?

According to Faradays law The changing flux will generate voltage in the secondary winding/circuit, so if the N2 = 2*N1, then the U2 =2*U1, and according to conservation of energy in that case I1 = 2*...
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How is the current density derived?

I would like to know how the formula $J= \sigma E$ Our teacher said that all of the books never really explained how they found the question, so I assumed someone here knows the equation.
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40 views

How electric current is defined in a metal wire?

How current is defined if in a metal wire both positive and negative charge exist? Isn't the total charge/time 0?
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4answers
59 views

How can there will be current in purely inductive circuit? [closed]

In a purely inductive circiut there are two emf's one is applied and other is induced applied emf and induced emf are equal and opposite, then how can there will be current in a purely inductive ...
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2answers
52 views

What are the Possible Dangers of an Overheating Household Wire? [closed]

Can anyone tell me any possible dangers/risks that could happen if a wire overheats even if it's insulated properly?
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1answer
17 views

Why does previously rotating DC Motors not generate sparks?

Yesterday I was playing around with a small DC Motor ,(ones which you can find inside a toy) and found something interesting. I took a cell and fixed one terminal of the cell to a terminal of the ...
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1answer
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Photoelectric Current [duplicate]

Recently learnt that Intensity= nhv ; where n is the number of photos per unit area My textbook specifies that the photoelectric current only depends upon the number of photons striking per unit time ...
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1answer
55 views

Electricity and light bulbs [closed]

Kindly say if I am right? Case1: Current flow and light from an incandescent bulb. Reason for light due to current flow: Tungsten is an insulator (comparatively) so when sufficiently high ...
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Current in a loosely coupled transformer [closed]

How does the secondary current depend on the resistive load placed on the secondary winding of a loosely coupled transformer, in which the primary winding is supplied with a linear current ramp ?
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6answers
1k views

Does the resistance of the voltmeter affect the behavior of this circuit?

I have this setup. It consists of a battery of no internal resistance with voltage $V$ and a resistor with resistance $R$. It also consists of a voltmeter of some (not so large) resistance as good ...
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2answers
43 views

Power in a simple electrical circuit [closed]

In this picture, as we know power due to heating of the resistance is $V^2/R$ . Now, if we add a parallel resistance to the circuit, the power dissipated through this resistor is also $V^2/R$ ...
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2answers
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Electrical vs Heating Insulation

Let's say we have a 120V cable and a 600V cable, this means that the 600V needs more electrical insulation to prevent the insulator from exceeding its dielectric strength. But in the other case, the ...
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3answers
53 views

Brightness of lamp

Brightness of lamp (power) depends on two factors: Current which flows through the lamp. voltage (p.d) across the lamp. In the figure: When the variable resistance increases, what happens to the ...
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3answers
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Why is the change in resistance not directly proportional to the change in temperature?

Change of resistance with respect to temperature is defined as $$\frac{\mathrm{d}R}{R}=k\mathrm{d}T$$ where $k$ is a proportionality constant, $R$ the resistance, $T$ the temperature and $\mathrm{d}R$...
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2answers
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Is there (or was there) a unit of electric current based on Avogadros number or Coulombs constant?

This has to do with the SI definition of the Ampere. Why the quantity $2*10^{-7} $ Newtons in particular? It would make more sense to define 1 Ampere = 1 mole of electron charge per second. Which ...
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1answer
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Is there Electric Flux through a closed loop around a current wire?

In one of his lectures, Professor Walter Lewin is ammending Ampère's Law to include displacement current (i.e. It not only depends on the current that penetrates the loop, but also on the changing ...
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2answers
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Can we define rms current for pure inductive and capacitive ac circuit?

For a purely inductive and capacitive ac(sinusoidally varying) circuit, average power dissipated across a capacitor or an inductor is zero. Then does that mean RMS current is zero?
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3answers
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Basic question about electric shock

When we are negatively charged, and we touch a doorknob for example, why does the shock happen (i.e. the flow of charge)? I understand that the electrons want to flow to positive charges, and I know ...
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1answer
38 views

Calculate the voltage between terminals a and b [closed]

Calculate the voltage between terminals a and b before and after connecting the external resistance R, then calculate absolute and relative difference of these voltages.
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Why High Voltage Power Lines need more Insulation than a low one?

"A 400 kV cable requires less insulation than a 240V cable." This was regarded as False in one of my question papers, but why? Doesn't a higher voltage means, lower current(P=V. I) and a lower ...
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1answer
32 views

When two wires touch, electrons can flow from one to the other. Is that a metallic bond?

If two very hot wires touch, they melt together to form one wire and electrons can flow between them. If two cold wires touch, they do not melt together to form one wire but electrons can still flow ...
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2answers
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What are the differences of two electron current?

I often see two definition of current in the book and literature, and I am a little bit confused. The current density $$\textbf{J}_1(\textbf{r})=\frac{-ie\hbar}{2m_e}\sum\limits_{n\textbf{k}}\{\psi^*...
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0answers
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Power dissipated through bulb decreases to a steady value

The instant at which bulb is switched on, its power is maximum, then it decreases to a steady value. This can be explained by the increasing resistance due to heating of the filament. (P = V*2*/R). ...
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2answers
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How far do electrons actually move along a conductor under an alternating current?

This is more or less a curiosity question. But I have had really good luck with stack exchange so far. If I can expand on my question a little bit - it may not be super important, but I know under say ...
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2answers
66 views

A “lightning” came out of the outlet and shocked me. How?

I was sitting in my bed using my computer. It was almost out of battery, so I got up and grabbed the charger to connect to the outlet. Then a strange thing happened: when my hand got near the outlet, ...
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2answers
67 views

Current without EMF in AC capacitance circuit

In AC circuit with only capacitance, current in circuit is maximum at time t=0 but emf of source is E=0 at t=0 , how can this happen, How can current flows without emf.
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3answers
98 views

Ampère's circuital law in case of uniform current density in infinite space

Let's have an ideal conductor with current density $\mathbf{J}$. The ideal conductor takes up the entire space, effectively resulting in the entire space $\mathbb{R}^3$ being permeated with $\mathbf J$...
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Is it correct to say that a smartphone cable is only a “1A” cable? [migrated]

A store owner said that some lower quality smartphone charging cables are only "1A cables", so if you want 2A, those cables won't do the job. Is it correct to say a cable is only 1A? Does the metal ...
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4answers
112 views

Basics of electric current

I am a mathematician who never took a physics class besides classical mechanics. Recently I have been looking at biophysics for a small project and I have a hard time understanding the basics of ...
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1answer
28 views

How are free electrons produced in a gas?

I'm aware about ionisation but even to ionise a gas you need an electron. So how in a discharge tube, which has a low pressure gas and a high voltage, does current flow? How is the first electron ...
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1answer
38 views

Can a strong electric field cause the electrons to come out of the atoms?

Can a strong electric field cause the electrons to come out of the atoms, is this how free electron are obtained in a discharge tube?
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2answers
44 views

Is (DC/battery) voltage a result of charge? or energy? or both?

Backstory: I’m a software engineer just getting into electronics and it seems that everything I’ve ever been told about electricity my whole life is a candy-coated lie. I can’t find consistent logical ...
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4answers
99 views

How does resistance *really* work? (DC, battery, LED, atoms, electrons)

Backstory: I’m a software engineer just getting into electronics and it seems that everything I’ve ever been told about electricity my whole life is a candy-coated lie. I can’t find consistent logical ...
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1answer
40 views

Skin effect prevailing the drift velocity effect

In general, an electron will propagate randomly in a conductor at the Fermi velocity( produced due to thermal energy of the conductor). An applied electric field will give this random motion a small ...
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0answers
24 views

Can an Opposing Current Create another Opposing Current?

In Inductors when current increases it's magnetic field induces a voltage which causes an opposing current that slows down the rise of the current that initially creates it, but can this opposing ...
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1answer
29 views

About Supercurrent Direction in London Theory of Supercondutivity

I'm studying superconductivity starting from London's approach. After you obtain the two London's eqs you get for the static case: $\quad \nabla^2 \textbf{B}=\frac{1}{\lambda_L^2}\textbf{B}$ If ...
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4answers
79 views

How does an ideal transformer satisfy law of conservation?

I have read in books and articles that, keeping the power as is transformers increase the voltage and therefore reduce the current as per the formula $$ P = IV $$ and this results to reduction in ...
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1answer
34 views

What is difference between current and voltage? [closed]

If current passes through the bulb not using it up then how battery becomes weak after sometime?