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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4answers
310 views

Potential difference across a capacitor

Look at the above circuit, I didn't get anything of it. Firstly i tried it using Kirchoff's voltage rule, I failed. I'm confused with those batteries. Can someone please explain me the role of those ...
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2answers
449 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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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
134 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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It is possible that without resistance current flow a conductor [on hold]

It is possible that without resistance current flow a conductor (answer with proof by)
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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
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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
78 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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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
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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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202 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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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
30 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
43 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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4answers
585 views

Current from Middle Battery in a Two-looped Circuit

With this question, as with many tutorials of similar questions I’ve found online, my textbook only mentions three currents: $I_1$, which flows through the left loop from and to the 19 V battery, $I_2$...
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1answer
124 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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2answers
501 views

Current in discharging capacitor through fixed resistor?

In the textbook I'm using for physics it says that the charge left on the plates of a capacitor after time $t$, that is discharging through a fixed resistor, is $Q=Q_0e^{-t/\tau}$ where $\tau=RC$ is ...
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4answers
89 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
477 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
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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
34 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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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
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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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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
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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
865 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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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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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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75 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
96 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
34 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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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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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
58 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
22 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
238 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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1answer
2k views

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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4answers
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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
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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
115 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
40 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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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 ...
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3answers
142 views

Current in only inductive AC circuit

Current through a LR circuit is given by $$i=i_0 (1-e^{\frac{-tR}{L}})..1$$From here I can observe that as I tend R towards 0 no current flows through the circuit , and current will be 0 when the ...
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2answers
153 views

Stacking batteries and electron flow

About Fuel Cells and Batteries: I understand the analogue with increased water height as two cells (battery or fuel) are connected in series. However if we for instance have two batteries contected in ...