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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344 views

Electric power for current density

The electric power produced by a current $I\in\mathbb{R}^+$ and a voltage $V\in\mathbb{R}^+$ is $$ P = IV. $$ Now the current is given as an (alternating) current density ...
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1answer
430 views

quantum mechanics current operators

How to derive the charge current and the energy current operators in second quantized form in Quantum mechanics ? Also if you could comment in a similar way on the entropy current operator, that will ...
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3answers
5k views

Will current pass without any resistance?

I've learned that a resistor converts some electrical energy into heat energy while the current flows through it and thus causes a power loss, but what if there's not any resistor in a circuit. Will ...
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5answers
725 views

Difference between ways of transmitting power

There are two ways to transmit the same amount of power, 1 amp at 1 million volts or 1 million amps at 1 volt. Conceptually what is the difference? How can I think about it conceptually? I would ...
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0answers
170 views

What happens if torque = 0?

I am trying to understand torque on a current loop which is placed in a uniform $\vec{B}$-field. (http://i.stack.imgur.com/oNO8a.jpg) It says that $\vec{F}_2$ and $\vec{F}_4$ have the same ...
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2answers
225 views

Battery and current confusion?

How exactly does a battery produce a current in the circuit connected across its ends? I dont want to know the chemical reactions in the battery core, but just the essence of it. I believe it doesn't ...
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1answer
559 views

Charging by induction (and grounding)?

The very familiar phenomenon of charging by induction includes bringing a charged object near an uncharged sphere to induce a separation of charges in it and then grounding the charge (same as the ...
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0answers
421 views

Relationship between current, voltage, magnetic field in a torus

I'm trying to find the relation between current density $\boldsymbol{j}$, voltage $v$, and magnetic field $\boldsymbol{B}$ for the time-harmonic approximation in a cylindrically-symmetric coil (a ...
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2answers
166 views

How does current flow in a irregularly shaped heterogeneous resistor?

The motivation for my question is understanding how electricity gets through your skin as opposed to running along it, and how the presence of things like water on the skin affect the relative ...
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2answers
373 views

How does symmetry allow a rapid determination of the current between $A$ and $B$?

The following was originally given to me as a homework question at my physics 2 course: Consider the following circuit The difference of potentials between the point $V_{1}$and the ...
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0answers
107 views

About electric current analogy

my teacher gave me this analogy to the electric current , the wire is like a pearl necklace where the pearls can move, the current or the movement of electrons is like putting your fingers between 2 ...
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1answer
392 views

Induced voltage of a conductor in a magnetic field

A book which I referenced for Electrical Machinery states that the voltage induced in a conductor inside a magnetic field is given by $$ \mathcal{E}=(\mathbf{v} \times \mathbf{B})\cdot \mathbf{l}$$ ...
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3answers
415 views

Which quantity gives the resistance of a component?

In a current vs potential difference graph, we can obtain the value of the resistance of the component. There are books that say gradient-inverse is the resistance and also books that say the value of ...
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1answer
1k views

Does rubber insulate lightning more effectively than air?

Last week, an Ars Technica writer was struck by lightning. He says that the 911 operators were concerned about whether or not he was wearing shoes at the time, but he didn't think it would make much ...
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1answer
392 views

Why should a battery not give current in order to measure EMF?

Emf is the "potential difference (PD) across the terminals of a battery when it is giving no current to the circuit." What does "when it is giving no current mean"? Will the PD across the terminals ...
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2answers
134 views

Electric power transmission

If we want to transmit electic current for a long distance, we must minimize a heat that releases because of the resistanse. We cannot make a cable wide because it is expensive and it will be massive. ...
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3answers
1k views

Can a current carrying loop or wire produces no magnetic field?

A current carrying wire produces magnetic field around it. We can find the direction by Fleming's Right hand rule. We know change in electric filed produces magnetic field and change on magnetic field ...
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1answer
4k views

Volts, Amps, and Practical Electrical Knowledge [duplicate]

I've heard people say that high amperage or high voltage is dangerous to humans-aren't they both? And what are the advantages to high amperage versus high voltage? And how do you generate one or the ...
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2answers
121 views

Currents and the Speed of Light

Why is it that currents don't flow at the speed of light, but rather significant ratios of the speed of light. I don't have any formal reasoning as to why they would flow at the speed of light-I just ...
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1answer
1k views

Speakers and Static from Hands

Why is it that when you touch the a bare male end of a speaker feed that the speaker makes hissing noises? Is it just (eddy?) currents running through you?
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2answers
280 views

Simple ohms law on a battery ? Paradox or conceptual error?

Suppose we have a regular pencil battery which supplies DC voltage $V$. Say we take copper wire and connect the ends of the battery to an $R$ ohms resistance. Then Ohm's law tells use the current in ...
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1answer
203 views

iPhone compass not being affected by current

As you probably know, electrical current and magnetic fields are close friends. In an iPhone there is a compass, however there are also lots of cables and in all of them, or at least in most of them ...
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4answers
3k views

North and south of magnetic field

The current I is flowing upward in the wire in this figure. The direction of the magnetic filed due to the current can be determined by the right hand rule. Can we determine the north and the south ...
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3answers
1k views

There must be free positive charges, moving oppositely to electrons for the wire with current to stay neutral

All popular expositions (e.g. these ones) of relativistic electromagnetism claim univocally that electrons in motion become more dense due to the speed. They teach that Lorentz contraction of charges ...
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3answers
2k views

What does it mean for electric current to be a scalar?

After reading the reasons for considering electric current as a scalar quantity, I was confused at a point which read "The magnitude and direction of current does not depend upon the direction of the ...
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1answer
416 views

Is it possible create current by spinning a charged sphere?

If we have a sphere which has $σ$ surface charge density and rotate it in axis z will this create current ? Is it possible without any potential difference ?
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2k views

Light bulbs, Wattage meaning? [closed]

Light bulbs, Wattage meaning? Two incandescent bulbs (120 V, 25 Watt) and (120 V, 500 Watt) connected to the same batteries. Which one shines brighter? And why?
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1answer
164 views

Understanding drift velocities in currents

I have a doubt about the understanding of drift velocities in a current. My problem is that the textbook speaks very loosely about this. It's like: "well, if we apply a field $E$ then the charges will ...
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1answer
170 views

Negative emf in AC generator

At a certain instant in AC generator, when the normal of the plane (rectangular coil) makes an angle of 270 degrees with with the magnetic induction B, the value of emf is: $E = -NAB\omega$ My ...
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76 views

Current between supeconducting rings

How to calculate the current between two superconducting rings with radius r separated by a distance d? Please note that being unfamiliar to the concept of superconducting rings, I can't approach ...
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1answer
264 views

Supersymmetric Noether theorem and supercurrents — invariance requirements

Consider $\mathcal{N}=1,d=4$ SUSY with $n$ chiral superfields $\Phi^i,$ Kaehler potential $K,$ superpotential $W$ and action ($\overline{\Phi}_i$ is complex conjugate of $\Phi^i$) $$ S= \int d^4x ...
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0answers
61 views

What works on 8-10 volts, 4 milli amps, and is not hardwired? [closed]

I want to know what is the smallest device that can work on a few milli amps? I know a NE-2 neon bulb works on less than 10 mAmp but on 90 volts at least. I need to find a small device that: 1- ...
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1answer
2k views

AC passed to a DC motor

What would happen when an alternating current (AC) is passed to a DC motor? And a direct current (DC) passed to an AC motor? Will it work or not? What will happen to it?
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2answers
2k views

Frequency Response RLC circuit - Current against Frequency graph - Symmetry?

I understand that in a Frequency Response experiment dealing with an RLC circuit, the graph of Current against Frequency is supposed to be symmetrical about the resonant frequency theoretically. ...
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5answers
29k views

Why is AC more “dangerous” than DC?

After going through several forums, I became more confused whether it is DC or AC that is more dangerous. In my text book, it is written that the peak value of AC is greater than that of DC, which is ...
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1answer
329 views

Eddy current losses in electric steel by harmonics of a magnetic field

I am working on an model of a permanent magnet synchronous machine. Right now I am stuck with calculating the eddy current losses caused by the harmonics of the stator magnetic field in the electrical ...
3
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1answer
299 views

Flow of supercurrent in a superconductor

I have two questions one practical and one theoretical. Even though I have a decent understanding of superconductivity both phenomenological as well as theoretical (i.e. BCS), some things just slipped ...
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3answers
4k 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
253 views

Why in $F = iLB$, $L$ is a vector but $i$ is not?

I learned $F = iLB$ recently. However, I don't understand why $L$ is marked as a vector but $i$ is not. For a normal rod, how should I define the direction of length vector $L$? And if I reverse the ...
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1answer
151 views

current electricity and voltaic cell

let us consider that i have a voltaic cell in an open circuit that has copper plate at higher potential w.r.t zinc plate. Now my query is, since the electrolyte separating them is a conducting medium, ...
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6answers
10k views

Parallel circuits - Overall resistance decreases with additional resistor [closed]

Let's say that there is a parallel circuit with two identical resistors in parallel with each other. If a third resistor, identical to the other two, is added in parallel with the first two, the ...
3
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2answers
1k views

Round bulb and Long bulb in Series Circuit

If you have a series circuit with a battery, one round bulb (with thicker filament), and one long bulb (with thinner filament), the round bulb does not light up and only the long bulb lights up. ...
4
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3answers
4k views

Capacitor circuits with light bulb

Let's say we have a normal circuit with a light bulb, with wires and a battery. When one places a capacitor in this circuit, how is the light bulb able to light up, even when the capacitor prevents ...
0
votes
1answer
3k views

Relationship between resistance and voltage drop

In a series or parallel circuit, if two bulbs have the same resistance, do they have the same voltage drops? The problem I am asking about is below. Do A, B, and C have the same voltage drops since ...
2
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1answer
103 views

Which of these two methods is correct for calculating current?

I recently came across a question, for which I saw two possible methods of finding the solution. I was required to calculate the "current flowing" $I$ when given the voltage $V$, frequency $f$, total ...
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6answers
2k views

Is voltage electric potential or electric potential difference?

On Wikipedia, voltage is defined to be the electric potential difference. However, I am still not certain as to whether voltage is the electric potential ($PE/q$) or electric potential change ...
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3answers
2k views

How is possible for current to flow so fast when charge flows so slow?

How is possible for current to flow so fast when charge flows so slow? We know electrons travel very slowly while charge travels at ~the speed of light.
2
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2answers
4k views

Ohmic and Non-Ohmic devices

Why do some conductors follow Ohm's law and some do not? Isn't there any universal law that can explain the flow of current?
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3answers
3k views

Why does the current stay the same in a circuit?

I was informed that in a circuit, the current will stay the same, and this is why the lightbulbs will light up (because in order for the current to stay the same, the drift speed of the electrons need ...
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2answers
514 views

Under what condition charges do not flow in closed circuit?

I wanted to ask under what conditions will charges not flow in a closed circuit. Or when is current through the circuit zero even when an EMF is applied? Like in the case of potentiometer, we say that ...