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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
69 views

Creation of electric field inside a conductor

My book says that as soon as the two ends of a conducting wire touches the two terminals of a battery, it generates an electric field inside the conductor. Why?
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27 views

Solving resistance using symmetry

Recently I've been studying current electricity and I saw many books using symmetry to solve circuits. broadly categorised as left/right symmetry and up/down symmetry where we take current to be ...
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1answer
36 views

Small current through a wire [closed]

Hi I dont know a great deal about electronics but I wondering if anybody can help me. I am making a small experiment and I want to send a very small current through a thin bare wire. I was thinking of ...
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14 views

How relative positions of battery and galvanometer affect the sensitivity of a wheatstone bridge?

I know one of the factors that affect the sensitivity of the galvanometer is the relative magnitudes of the resistances in the four arms of the bridge. the bridge is most sensitive when all the four ...
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2answers
496 views

Why do we use a specific point to find the resistance of a non-ohmic conductor? Why not tangent?

I was wondering why can't the tangent be used to do this calculation? Can a randomly chosen point be used?
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2answers
185 views

The importance and the role of a switch in an electrical circuit

There is this simple test: Three identical bulbs are connected in the circuit illustrated in the figure. When switch $S$ is closed: a] The brightness of $A$ and $B$ remains the same, while $C$ goes ...
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1answer
2k views

How does a voltage independent current source work?

I'm having some trouble understanding what a voltage-independent current source is. How can you have a current without a voltage? As I understand it, voltage or EMF is the force that drives the ...
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5answers
25k views

Speed of light vs speed of electricity

If I arranged an experiment where light raced electricity what would be the results? Let's say a red laser is fired at the same time a switch is closed that applies 110 volts to a 12 gauge loop of ...
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6answers
160 views

Why is it assumed that magnetic forces arising from magnetic fields do not do work on a current carrying conductor?

Imagine a long, thin current carrying conductor carrying a current $I$ and moving through space with a velocity $\mathbf v$. If there exists a magnetic field such that there is a force on the current ...
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28 views

It is possible that without resistance current flow a conductor [closed]

It is possible that without resistance current flow a conductor (answer with proof by)
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0answers
23 views

Current-carrying wire in a magnetic field. Cross product, vectors and scalars

We have a wire with cross-sectional area $A$, length $L$ and current $I$. If the wire is in a magnetic field $\vec B$, the magnetic force on each charge is $\vec F =q\vec v_d \times \vec B$. $\vec ...
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1answer
35 views

Conversion of a galvanometer into a voltmeter

When we are given a question regarding conversion of a galvanometer into a voltmeter,we are given full scale deflection current and initial resistance of the galvanometer...then we are given the ...
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1answer
83 views

Demonstration that electric current at equilibrium is zero in crystals

As it is well known, electrons at equilibrium (no external field) do not conduct electric current, i.e. $\int_{BZ} dk\,v_{k}\,f(\epsilon_k)=0$ where $f(\epsilon_k)$ is the Fermi-Dirac distribution $...
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5answers
17k views

How can one derive Ohm's Law? [duplicate]

I am looking for the derivation of Ohm's Law, i.e., $V$ is directly proportional to $I$. Can someone help me with it?
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1answer
45 views

Magnet position for maximum voltage in an ac generator (Lenz's Law)

Animated gif credit The picture above shows, that the voltage of a phase is greatest, when the magnet alligns with the coil of the phase. Why is that? To my knowledge of lenz's law the voltage and ...
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2answers
1k views

Inductive reactance 0 for dc current?

Inductive reactance: $$X_L=\omega L=2\pi f L$$ is the opposition to the flow of current by an inductor. Frequency $f$ being $0$ for a DC current, the inductive reactance too is $0$. But doesn't the ...
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2answers
269 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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How to measure transverse current-current correlation at arbitrary wave vector and frequency

Let $\hat J^{\mu}(t,\boldsymbol r) \equiv (c \hat \rho(t,\boldsymbol r), \hat{\boldsymbol J}(t,\boldsymbol r))$ be the density-current operator at spacetime coordinate $(t,\boldsymbol r)$, in the ...
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3answers
1k views

Voltage and Electric Field in a Circuit

I have a doubt regarding how the electric field acts in a circuit. I have been told that a normal cell creates a uniform electric field, but I find it a bit confusing. Let me explain my doubt with a ...
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1answer
37 views

Some confusion in Drude theory of metals

Discussion on the drude theory of metal usually begin with the case of zero magnetic field so that the force acting on the electrons is just the one from the electric field. But then, this electric ...
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2answers
74 views

Can we apply ampere's law for a current carrying circular loop

They used the ampere law to calculate magnetic field by a toroid ( assuming perfectly circular coils provinding symmetry and neglecting effects due to helical nature) whis is $μ_0ni$(where $n$ is no ...
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1answer
125 views

Would a solenoid move if a magnet went through it?

If you were to have a solenoid (0 current) floating still in space, and shot a magnet through it, would the solenoid move, or would it only create a DC current (what if it has a closed/open circuit)? ...
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4answers
106 views

Why does inductor current lag the applied voltage at its terminal by 90 degrees?

I studied electromagnetism and I am currently working with Inductors. I could not figure out the physical reason based on electromagnetics on why inductor current lags the applied voltage by 90 ...
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3answers
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Found some errors in some equations of electric power. What is the actual problem?

I think the following two equations are incorrect when $I, R$ refers to current and resistance respectively and $V$ refers to potential in the difference of potential of the two sides of the resistor ...
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2answers
532 views

From where do electrons gain kinetic energy through a circuit?

Supposing an ideal wire, How do electrons accelerate and gain kinetic energy? What I understand: When a circuit is opened ,electrons are crowded at the negative term of the battery and have high ...
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1answer
48 views

Current in RC circuit

Why is current drawn in an RC circuit (in a circuit powered by DC voltage supply) independent of the capacitor used? While the capacitor is charging current drawn from the battery only depends on ...
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1answer
36 views

LCR circuit (AC source) potential difference across capacitor

For a LCR circuit connected to AC source of emf$$E= e\sin(ωt)$$ and let the current in LCR circuit be I then $$I=i*\sin(ωt+Φ)$$ then it is given that potential drop across the capacitor is V.ie$$V=-...
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1answer
22 views

Heating effect on metals

Why does a metal emit photon on heating? Where this photon came from as soon as the metal is heated? What makes the metal to emit photon while heating?
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3answers
108 views

Why the current is the same at all of the positions in a series circuit?

Why the current is the same at all of the positions in a series circuit? although there are different voltages at different positions of the circuit. What i know is that as the electron passes one ...
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3answers
37k views

How exactly does a resistance reduce current?

I've heard that resistors are used to decrease current to a particular appliance, such as in the regulator of a fan. However, I've also heard that the total current in a circuit is always the same- in ...
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4answers
11k views

How do electrons know which path to take in a circuit?

The current is maximum through those segments of a circuit that offer the least resistance. But how do electrons know beforehand that which path will resist their drift the least?
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7answers
19k views

Difference between current and voltage sources

I am confused about the current and voltage. My intuitive example would be that of a pipe of say water. The diameter of the pipe determines the amount of water flowing per second but the pressure is ...
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4answers
920 views

Ohm's law: Why is the voltage equal to the product of current and resistance?

I'm a bit confused I know V=potential difference of a conductor is the work done by the battery in pushing one charge across a conductor.This means it is inversely proportional to the number of ...
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6answers
6k views

Could someone intuitively explain to me Ohm's law?

Could someone intuitively explain to me Ohm's law? I understand what voltage is and how it is the electric potential energy and that it is the integral of the electric field strength etc. I also ...
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13answers
9k views

What *exactly* is electrical current, voltage, and resistance?

I am taking AP Physics right now (I'm a high school student) and we are learning about circuits, current, resistance, voltage, Ohm's Law, etc. I am looking for exact definitions of what current, ...
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5answers
33k views

Current in series resistors and voltage drop in parallel resistors

When we have resistors in series, the current through all the resistors is same and the voltage drop (or simply voltage) at each resistor is different. Question 1: It is fine that voltage drop (...
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1answer
2k views

Current in Parallel Circuits

For the parallel circuit below: Why is the current across the ammeter unchanged when the resistance of the variable resistor is increased? I've always learnt that current varies in parallel and ...
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3answers
81 views

Why voltage is same across parallel resistance?

Since voltage stands for energy per unit charge to be used to carry it from one point to another,why should energy per unit charge be same for two resistors of different resistances,?the energy ...
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3answers
101 views

Basic question on Ohm's law

I have what I assume is a very basic question on Ohm's law. Let's say that we have $n$ equal light bulbs in a series with a battery. We know that $$ U - IR - IR - \cdots -IR= U - nIR = 0.$$ Solving ...
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1answer
37 views

What is causing the current sinusoidal delay regarding voltage in inductive circuits? [duplicate]

Do electrons acquire some electromagnetic 'mass'as they have so much slow acceleration in the coil due to obviousely electromagnetic field acting on them or it is just the net voltage that drops down ...
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0answers
7 views

Calculation of eddy currents and subsequent heating in a metal, ATEX-rated junction box

We are building a system which will make use of a stainless steel junction box to connect different circuits within it. This will be located in a hazardous offshore environment so we will be using an ...
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0answers
20 views

Conventions for direction of current flow and forming a charge difference

I have explored many videos, postings, and lectures regarding the interaction of electricity, magnetism, and motion, including Fleming's Right Hand Rule and Left Hand Rule. While the explanations of ...
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1answer
65 views

What causes changes in frequency in the Nation Grid electricity supply? [duplicate]

Following the power cuts in Britain this week, we were told that lack of power being generated led to a drop in the AC frequency as shown in this graph: I understand why a stable frequency is ...
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1answer
24 views

Relation Between Current and velocity of electrons

In a conductor, all the electrons are few to move to conduction bands. If we say that magnitude Current is increased (I= dq/dt) can we infer that the velocity with which the electrons flow also ...
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1answer
297 views

Difference between bound and free charge/current in a perfect conductor

For the case of charge, it seems clear that in a perfect conductor the free charge refers to the excess charge that has been dumped into the conductor, while the bound charge refers to the charge that ...
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4answers
1k views

Electromagnetic field and voltage drop in a circuit

I have been thinking for a while about what really causes voltage drop and how to explain it in terms of what the electric and magnetic fields do. So I've been reading a lot of posts here and in other ...
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1answer
17 views

How to use the definition of volume current density?

The volume current density $ J$ is defined as $ \frac {dI}{da_{\perp}}$ where $dI$ is a small current segment flowing in the volume with cross section $da_{\perp}$ where $da_{\perp}$ is a small area ...
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1answer
123 views

Can Polarization Current Density be a tensor quantity?

I've seen a definition of Polarization Current Density (usually given when explaining displacement current) given by: $$\vec{J}_P=\frac{d\vec{P}}{dt}$$ But this seems to not contain all the ...
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1answer
41 views

The currect density in materials of uniform resistivity

Inside an infinitely large piece of material that fills the whole $\mathbb R^3$ space with uniform resistivity $\lambda$ (which letter should I use, when $\rho$ has been used for charge density?), ...
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3answers
67 views

Constant Current Conundrum [duplicate]

Say we have a simple circuit with three resistors in series, each of which have the same resistance. We also have a battery with a given constant potential difference hooked up in series with these ...