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
247 views

Faraday's law and “infinite induction”

I may have confused after thinking too much about Faraday's law. If an emf is induced in a circuit due to some changing magnetic field, the induced current will be in a direction such that the ...
2
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1answer
279 views

Ampere's circuital law for finite current carrying wire

When I was studying about Ampere's circuital law. Then there comes a question in my mind that "whether this law is applicable for finite current carrying wire or not"
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0answers
25 views

Drift velocity in Silicon wafer

I have been asked the following question in a problem sheet: A $100mm$ diameter, $0.5mm$ thick silicon wafer at room temperature has a charge carrier density of $1.5×10^{10} cm^{-3}$. A potential ...
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3answers
12k 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 ...
2
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0answers
29 views

Current density defined by the scattering operator

I have a problem with the definition of the current density. In most literature it is defined as $j^\mu=\frac{i}{2}(S^*\frac{\partial S(A)}{\partial A_\mu(x)})$. I understand that normally we use ...
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2answers
49 views

Which is more important, current or potential difference?

If i have a bulb rated 4V, 4A, and my power source is 2V, 2A. Should I use a step up or step down transformer to make it 4V, 1A or 1V, 4A? Which wold make it glow brighter?
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1answer
42 views

Resistance and potential difference across it

I have this question that has baffled me for hours now. My question is what really happens when charge passes from one point to another in a circuit for eg what happens when it passes over a ...
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1answer
25 views

How to implement the form of current density in a Hall Effect related calculation?

Please consider the following; Question. A rectangular plate of semiconducting material has dimensions 10mm x 4mm x 1mm. A current of 3 mA flows along the length and a Hall Voltage of 13.6 mV is ...
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0answers
57 views

Current Density Boundary Conditions and its Implications

According to Ohm's Law, one can say $ \overline{J} =\sigma \overline{E} $ if the field is in a conductor, and $ \overline{J} =0 $ if it's in empty space. Now if we take the surface of a conductor and ...
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1answer
127 views

Resistor cube problem solving method

I was solving problems from Irodov when I came across the method called point of symmetry method. I cant find this method anywhere. So what is this method? Here is the link to the problem solution ...
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0answers
15 views

Is their a visual difference between air-gap sparks of the same voltage but different current?

For example, if this spark gap has a kilovolt of power behind it @ 1A and the other is also at a kilovolt but is @2A will there be a visual difference (i.e. will the one with higher current be ...
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0answers
22 views

Is it possible to raise the voltage of a power source by lowering its current indefinitely (i.e. transformers)?

Let's say you have a D battery. You wire it up to the primary of a step-up transformer, which you then in turn wire up to another step-up transformer,...etc. Is there a limit to how high the voltage ...
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3answers
44 views

The standard definition of current

The book says current is the rate of flow of charge per unit time, but I don't understand whether it is rate of flow of charge through a single cross-sectional area per unit time or the entire amount ...
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2answers
64 views

How do you calculate maximum current density for alternating currents?

I think the answer is neither here nor on Wikipedia but forgive me if it is, I don't read maths well. This question applies specifically to current density during transcranial stimulation with either ...
0
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0answers
28 views

Calculating current on power line from induced voltage on nearby loop

The question I'm having trouble with is: A small circular loop of 5mm radius is placed 1 meter away from a 60Hz power line. The voltage induced on this loop is measured at 0.6 microvolts. What is the ...
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0answers
54 views

Noether Current and Feynman Diagrams

My question is simple. Assume that there is no anomaly and we have found from the lagrangian that there is a conserved current. I want to know what this means in terms of feynman diagrams, not in ...
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1answer
72 views

The image current due to moving charges and a current carrying thin wire

Suppose we have a plane conductor and positive charged particles of mass m are moving parallel to the plane conductor at a distance d. The trajectory can be assumed to be straight. An image current ...
5
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4answers
10k views

Is it possible to flow current in open circuit?

As I know a battery is an example of a closed circuit where it can then produce electricity , electrons will flow from negative pole to positive. A chemistry representation of this battery is for ...
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3answers
42 views

Where to start from and how to proceed for finding the resistance here? [closed]

Can anyone kindly help me in finding the effective resistance between A and B in the below goven case ? Each resistor is of 16 ohm .. Thank you .
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2answers
57 views

What should the length of my wire be in order to get a surface area of 10cm^2?

I would like to make a flat coil out of a steel wire that is $1.22 ~\text{mm}$ in thickness (or $1.22~\text{mm}$ in diameter). I wish to make the coil up the wire into a flat disk that has a surface ...
2
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2answers
160 views

Does “ac current” mean that the electricity goes left and right or just changes polarity?

AC goes one way in one phase and the opposite way in the other phase, but is going right and to left, or is it only changing the polarity from (-) to (+)? If light bulbs turn off and on (so fast we ...
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1answer
20 views

Magnetic field between two rings

Two rings are placed parallel atop each other along an axis with a distance $\epsilon$ which is much smaller than the radius of both rings a. Through one of the rings there is a current I and through ...
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1answer
34 views

Current and current density

Current, $I$, is generalised as: $I=\iint_{A}^{} \vec{J}. d\vec{A}$. I know that current density always points in the direction of flow of positive charge. I wonder if the infinitesimal element, ...
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4answers
1k views

How can there be a current and an electric field in an idealized wire with no voltage drop?

In an ideal circuit, How can there be a current b/w points a & b, when there is no potential difference and thus no electric field between a & b? If there is no current, then where does ...
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3answers
61 views

What does it mean when we say that power of a bulb is 10 W? Since $V/I=$ resistance is a constant, how can power $=VI$ be a constant?

My question is simple. In Ideal situation, at constant temperature, we know that normal appliances like a filament bulb has straight Voltage vs Current graph, meaning its resistance is constant or ...
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0answers
27 views

What is the physical meaning of $\overline{\Psi} \Psi$ in the Dirac current's “Gordon Decomposition”?

When writing the Dirac (charge) current out in a way that resembles the (charge) current in the Pauli/Schrödinger theories, one obtains the following: $ j^\mu = -\frac{\mathrm{i} e\hbar}{2m} \left[ ...
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4answers
184 views

Ohm's Law Question?

Since $V=IR$, if you were to have say a $5\:\mathrm{V}$ source connected directly to ground, no components in the circuit at all, you would need to add resistance for the current to flow? Or is there ...
0
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2answers
58 views

Is it low current or low voltage that dims a bulb?

At times we have dim bulbs due to some fault from national grid, what I want to know is if this fault is low current or low voltage. Other times electrical appliances blow-up, is that high current or ...
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1answer
33 views

current flow between two points

I can measure a voltage that is induced on my skin from a 50hz electromagnetic field (emf) source using a multimeter, how can I measure the induced current flowing between my finger and ground when I ...
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1answer
36 views

Why does 50/60hz waveform sometimes appear to change direction when imaged on an oscilloscope?

http://www.shutterstock.com/video/clip-32898-stock-footage-an-old-oscilloscope-demonstrates-a-waveform.html The video above displays a waveform moving from left to right. This is generally how my ...
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1answer
111 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 ...
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1answer
39 views

Is the magnetic field calculated by Ampere's Law only because of the currents crossing the loop? [duplicate]

In Ampere's Law, $$\oint \vec B \cdot \mathrm d \vec l = \mu I$$ the current outside the curve is not included on the right hand side of the equation.* Does it mean that the magnetic ...
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1answer
36 views

Is there an electric field in the direction of a uniform current?

In an infinite plane where uniform current is passing through,is there any electric field? Because i know that charge produces an electric field but in a uniform current and because it is an infinite ...
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0answers
14 views

What is the effect of a magnetic field on a plasma speaker?

I have been doing some research for the past couple years investigating the effect of a magnetic field on a plasma speaker. More specifically, if you apply a relatively uniform magnetic field in no ...
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0answers
38 views

How to apply voltage source in FEM when solve Maxwell equation?

I need to solve the Maxwell equation of electric field by finite element method. In this function, the right hand side is the current density. However, in my problem, the voltage source with 1 MHz ...
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2answers
121 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 ...
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1answer
70 views

Filament lamp: Negative part of I/V characteristic?

I don't understand the negative part of the graph. It shows that the resistance is decreasing as the voltage goes from negative towards 0. What does a negative voltage mean and why does the graph ...
2
votes
2answers
43 views

How is resistance defined when there is no current?

By definition, a component has a resistance of $1\Omega$ if a potential difference of $1$V makes a current of $1$A flow through it. So I was a bit confused when I saw somewhere "a filament lamp has a ...
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1answer
19 views

Inductor in transformer

In an inductor, a current waveform 90 degrees out of phase with the voltage waveform creates a condition where power is alternately absorbed and returned to the circuit by the inductor. If the ...
1
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0answers
43 views

Is shaking a phone enough energy to charge a smartphone?

Is shaking a phone enough energy to charge a smartphone? For example I'd like to use some kind of power generator to charge smartphone's battery but I'm wondering if shaking (by hand, or motion when ...
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1answer
35 views

How is the efficiency of an electric motor affected? [closed]

Consider that I'm having a motor (AC/DC) and the power switch is on and it's being supplied power and of course the motor is rotating. Now, I continuously start switching off and on the power. For 1 ...
1
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2answers
55 views

What is the rigorous definition for current in a closed circuit?

I know that $I = \frac {dq} {dt}$, but I have trouble reconciling that derivative definition with my intuitive understanding of current. At an arbitrary point in wire, the current is obviously the ...
3
votes
1answer
134 views

does a resistor slow down the flow of electrons or just let less electrons through? or is it both?

I like to have an intuitive grasp of whats happening our tutor said they 'resist' the flow of electrons but I want to understand exactly whats happening.
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1answer
48 views

Can Ampere's Circuital law be used on an infinite number of alternating Helmholtz coils?

I have the following surface current density $$ \bar{\sigma}_s = \hat{\phi} \sin(kz) |\bar{\sigma}_s| $$ to approximate an infinite number of alternating Helmholtz coils stacked along the z-axis with ...
3
votes
1answer
117 views

Why is the quench temperature fluctuation not a concern for maglev trains?

I am having trouble discovering why temperature fluctuations and magnetic field fluctuations are not a stability concern for superconducting magnetic levitation trains. I am under the impression that ...
1
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0answers
127 views

Earth magnetic field [closed]

I gather that, in these days, the most common explanation for the Earth magnetic field existence and strength is the theory of convetive currents of molten iron and nickel atoms in the outer core of ...
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1answer
41 views

What would you do to measure wind speed below 50m?

Is there a radiation spectrum that could be used near the surface of the earth to fluoresce air enough to see the currents? Is there a complimentary CCD that can image that spectrum? I am looking for ...
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1answer
564 views

What would be the resistance of a wire, if it is stretched to double length? [closed]

If there is a wire of resistance $R$ and we stretch it such that it becomes 2 times longer, then what should be the new resistance of the wire?
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2answers
116 views

Does a battery in a vacuum produce a current?

I've always assumed that the strong resistance of air is the reason there is no flow of electrons between the terminals of a battery until a wire is connect. However, in a vacuum there is no resistive ...
0
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3answers
8k 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?