A measure of the rate at which electric charge is transported (especially through a circuit), it has units of charge/time.

learn more… | top users | synonyms

-1
votes
0answers
17 views

Resistance in Potentiometer [on hold]

A potentiometer is shown in the figure. a) How will the balancing length be affected if resistance (R) is increased or decreased ? b) Will the balancing length be affected if resistance (S) is ...
0
votes
0answers
15 views

Free charge density and current in an ohmic material

I have come across what seems a paradox -or at least an exotic conclusion- regarding current conduction in an ohmic material. It is well known that free charge density can only be zero on an ohmic ...
1
vote
2answers
33 views

Why can't I connection the anode of a battery to the cathode of an other battery and get a current flowing?

If I touch the anode of a battery or connect the anode the the cathode of an other battery, none (or rather: a very small current) flows between those two. If I instead connect the connect the anode ...
-1
votes
0answers
22 views

Confusions about current, voltage and capacitors [on hold]

If it's okay I have a few quastions. First of all, what is current. I've had people tell me it's negativ charges moving but also that it's negativ and positiv charges moving in different directions. ...
0
votes
1answer
37 views

Probability flux: spatial variation of the phase equal to momentum?

We can write any wave function as $$\psi(\vec x, t) = \sqrt{\rho(\vec x,t)}\exp{\left[\frac{iS(\vec x,t)}{\hbar}\right]}$$ for $S$ real and $\rho >0$. Here we interpret $\rho$ as the probability ...
1
vote
2answers
46 views

Does the speed of electrons depend on energy?

I would like to know whether the speed of an electron depends on energy. If yes then in a circuit when electrons flow out of a resistor the energy decreases by a considerable amount, leading to the ...
0
votes
0answers
14 views

Flow of alternating current in an ac circuit

I know that it the frequency of an alternating current is 50Hz.It changes its polarity 50 times. So in a circuit does the polarity gets changed these many times. It seems that it is well applicable in ...
0
votes
0answers
13 views

Current flow in a polarized capcitor

What is a polarized capacitor? I have learned that in a polarized capacitor, the negative lead must be connected to the negative terminal of the battery and so the positive. But my doubt is that if ...
0
votes
0answers
28 views

Voltage in AC Currents [closed]

This is the graph representation of the voltage in an AC Current , my question is why is it increasing and decreasing and not constant ? I hope my question is clear now :)
0
votes
2answers
33 views

Finding current density?

I found (from here) that current density can be found with the formula: $$\vec j= \frac{dI}{ds} \vec a$$ where $s$ is the cross sectional area centred on the point we are considering and with a ...
0
votes
0answers
9 views

Magnetic field generated by wires with magnetic cores

Describe the magnetic field generated by alternating current as it passes through a wire's special core of tiny, metal-coated, cylindrical rare earth magnets? Examples of real-world consequences of ...
0
votes
1answer
14 views

Is the passive reference configuration different from the conventional direction of current?

Is the passive reference configuration different from the conventional direction of current? According to the passive reference configuration, current enters the positive polarity of voltage, while ...
0
votes
1answer
46 views

Forces on a wire moving in a magnetic field?

When a wire is placed inside a magnetic field and current starts to flow in that wire, that wire experiences the Lorentz force = $IL \times B$ and beings to move. Aside from induced motional - ...
3
votes
1answer
313 views

What proved Conventional sense wrong?

What fact proved for the first time that the conventional sense of current was wrong? And when it did happen? As a corollary of this question, why do we say that electrons have negative charge? Is it ...
0
votes
0answers
11 views

What causes a larger (longer) electrical arc when using a tesla coil

So, I really don't know much about this subject, if any at all, but I'd like to do a project on it. I've done some testing with my tesla coil and there appears to be a trend such that a larger ...
1
vote
4answers
85 views

Where does the energy of the electric cable come from?

I'm stuck on one really simple example, I can't figure out what's happening to energy here... (This is not homework) Let's consider an uncharged electric cable, we'll model it by an infinite ...
0
votes
1answer
32 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 ...
0
votes
2answers
72 views

Flow of electrons in electric current

In an electric circuit, how does the excitation of the free electrons to higher energy levels translate into net forward motion of the electrons to the positive terminal? My concept of electrons ...
0
votes
2answers
52 views

Optimal method for solving circuit

This problem seems quite simple, and I can easily find a way to solve it but the possibility of error in my method is extremely high. This is just a sub-task of a bigger task but this is the only part ...
0
votes
3answers
43 views

Electric warning signs question

I've always wandered why do the warning signs show the voltage, not the current. I mean, it's the current that kills you.
0
votes
1answer
44 views

Magnetic Wire Doesn't conduct Electricity

I recently bought a 22 and 30 gauge loop of magnetic wire from radio-shack. The loops of wire were colored differently (if this makes any difference) and on the package it noted how these wires were ...
20
votes
6answers
3k 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 ...
1
vote
1answer
48 views

Spherical Magnet Inside a Solenoid

When passing a bar magnet through a long solenoid why is it that the induced emf when the magnet is in the middle of the solenoid is zero? And if a spherical magnet is put inside the solenoid, will ...
1
vote
4answers
108 views

Why does a magnetic field go anticlockwise of the direction of current?

Why never clockwise? How does it 'know' to go anticlockwise?
0
votes
1answer
29 views

Relation between Power, Voltage and Current when one or more of them is amplified?

Power(P) = Voltage(V) * Current(I) If voltage or current is amplified or multiplied what happens to power and current. Does this affect in increase or decrease in power and current values or does ...
0
votes
2answers
81 views

How does a magnetic field “push” charges?

I was under the assumption that a magnetic field acts similar to that of the normal force in mechanics; both affect the path of the object, but do no work. So now suppose that we have a rectangular ...
0
votes
2answers
39 views

Ampere's law of circular path when “bulging” out

The picture shows a use of Ampere's law. A circular path is chosen. $$\oint \vec B \bullet \mathrm{d}\vec l=\mu_0 I_{encl}$$ When using Ampere's law we are talking about the current enclosed. That ...
0
votes
1answer
58 views

The graph of Alternating current

I am beginner Physics student and currently studying Alternating current. One thing that confuses me about this topic is the graph Voltage/Time. Now I know it is a sinusoid, but it is the ...
0
votes
1answer
47 views

Does current flow if the current density $J=\sigma f=0$?

A current density $J$ is proportional to the force per unit charge and is of the form $J=\sigma f$. In cases of a conductor where $\sigma=\infty$ and hence $f=0$, is it that current is moving so ...
0
votes
3answers
130 views

(Capacitance of a battery?) Finding the charge accumulated on a rod

We all know the expression for the potential difference across a conducting rod moving through a region with a uniform magnetic field: $\epsilon = B l v$ Now my question is different. Is it ...
3
votes
1answer
84 views

Why are charging times so long for Lithium-ion batteries?

Why do rechargeable batteries (e.g., mobile phone batteries) need sometimes several hours to be fully charged? In other words, what are the physical constraints that don't allow me to charge my iPhone ...
0
votes
0answers
14 views

Time domain reflectometry (TDR) used on conductive “block”, not wire

What would happen if you tried to use time domain reflectometry (TDR) on a conductive block, opposed to a wire? Using electrodes or something. If you could describe the physical behavior of the ...
0
votes
0answers
29 views

Li-ion Battery charging

Why are constant current mode and constant voltage mode needed when charging Li-ion batteries? Why do we apply saturation charge even after the cell voltage reaches 4.2V? What exactly is 'I-sense' in ...
1
vote
3answers
92 views

Defining Reference Directions for Voltage and Power (sign convention)

My professor decided to use the above reference directions when calculating power in circuits. He says that when power > 0, power is consumed. When p < 0, power is generated. This definition is ...
-1
votes
3answers
71 views

Why Voltage Drop is not Influenced by Resistor Value?

To my understanding, if a resistor reduces the potential energy of the current across it, then the current that leaves the resistor will have less potential energy and thus, less pressure or voltage. ...
0
votes
1answer
42 views

Mean-free-time between collisions and drift-velocity

In a physics text book I need help to make sense of the part highlighted in yellow: This is out of context of course, so just to make it clearer: $\tau$ is the mean free time of the electrons in a ...
0
votes
1answer
44 views

What is the equivalent of the “amount of fuel” for a battery?

I am trying to make a performance diagram of an electrical powered device vs range, speed, etc. I want to compare it using the equivalent of fuel for a battery? I am not sure if it is just voltage... ...
2
votes
1answer
85 views

Why does current density have a direction and not current?

As I understand it the definitions are as follows: Current is a scalar $I$ with units of $\mathrm{[J/s]}$. It is defined as $I=\frac{\mathrm{d}Q}{\mathrm{d}t}$. Current density is a vector $\vec{J}$ ...
1
vote
1answer
25 views

Drift velocity of charges in current

In an electric curcuit, charges (electrons e.g.) move randomly around very, very fast. When a current is set in a curcuit, the charges still move randomly, but have a drift velocity around the ...
0
votes
1answer
64 views

Opacity/Transparency of Conductive Meshes to Charged Particles (Electrons/Ions)

When using a conductive (metal) mesh, effectively a metallic woven fabric, in vacuum applications as a "grid" for charged particle optics, how does one calculate (or at least estimate) the opacity or ...
1
vote
1answer
42 views

Current in a fluorescent tube that is not in a circuit

In Walter Lewin's 8.02 Electricity and Magnetism course, he places a fluorescent tube pointing radially outwards from a large Van der Graaf (VDG) generator. Due to the VDG's E-field, this causes a ...
0
votes
7answers
155 views

Why Two Equal Resistors Cut Voltage in Half?

I've been reading several books on electronics, one of them called "Electronics All-In-One For Dummies - D. Lowe (Wiley, 2012) BBS". It states that if two resistors of the same value, no matter the ...
0
votes
1answer
49 views

does a coil generate emf if field passes near and not trough it?

So I was visiting this insctructable safety light for bikes which takes advantage of magnetic induction to get current and power some 2V red LEDs. How does it work if no magnetic field gets trough ...
0
votes
2answers
64 views

Is it possible to have both a conduction current and a displacement current at the same time?

According to Ampere's law, is it possible to have both a conduction current and a displacement current at the same time? In the classical derivation of the displacement current using a parallel plate ...
1
vote
1answer
46 views

Induced electric field due to a moving wire

An infinite wire carrying a constant current $I$ in the $\hat{z}$ direction is moving in the $y$ direction at a constant speed $v$. Find the electric field, in the quasistatic approximation, at the ...
2
votes
1answer
96 views

Trying to show that the current is conserved

$ \newcommand{\p}{\partial} $ I am trying to show that the current $J^{\mu} = (\gamma_{\nu}\partial^{\nu} \phi - m\phi)\gamma^{\mu}\psi$ is conserved for all fields that satisfy the Klein-Gordon and ...
0
votes
3answers
243 views

Why the bulb glows brighter?

If the total current is divided into the branches in a parallel configuration and it is constant in series. How come the bulbs glow brighter when connected in parallel than when connected in series?
0
votes
1answer
52 views

Formula for Magnetic field due to current loop

I need expressions for $B$ field off the axis due to current loop. The ones I came across on the internet aren't very convincing. I verified them with Mathematica, and none seems to be correct. I'm ...
0
votes
2answers
59 views

Whats the point in conserving electricity if the AC current produced cannot be stored?

If we cannot save the ac current produced in a battery or some device like the DC current there is no point in conserving it because current once produced should be consumed somehow!!
0
votes
2answers
66 views

Currents induced by rotation of a coil about magnetic field lines

If the coil on the left is rotated about the magnetic field lines, will there be an induced current? I know that the flux concerns only the component of the magnetic field perpendicular to the ...