Tagged Questions
2
votes
0answers
27 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 ...
1
vote
1answer
45 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
$$ \mathcal{E}=(\mathbf{v} \times \mathbf{B})\cdot \mathbf{l}$$
...
-1
votes
0answers
29 views
Displacement current in the Ampere equation [closed]
Does it explain the significance of displacement current in the Ampere equation?
4
votes
2answers
124 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 ...
1
vote
2answers
103 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 ...
2
votes
1answer
75 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 ...
1
vote
4answers
74 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 ...
-4
votes
3answers
190 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 ...
4
votes
2answers
117 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 ...
1
vote
1answer
51 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 ...
1
vote
1answer
48 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 ...
0
votes
0answers
42 views
Magnetic field at a point [closed]
Find the magnetic field near a straight current carrying conductor of Length $L$ and current $I$, at point located along the perpendicular bisector of the wire a distance $r$ from the wire. Show all ...
0
votes
1answer
141 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 ...
2
votes
4answers
121 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 ...
0
votes
1answer
63 views
how to find the diameter of this fuse? [closed]
A fuse blows if the current exceeds 1.0 A. It is made of material that melts at a current density
of 620A/cm2. What is the diameter of the wire, assumed to have a circular profile, in the
fuse?
0
votes
0answers
44 views
Object accelerated by electromagnet
If I have an electromagnet (powered by a battery) and a metallic object, the
power generated will depend on the voltage of the battery and the resistance of the coil.
If I accelerate the object, will ...
2
votes
2answers
134 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 ...
0
votes
0answers
153 views
RMS value of the A.C. current? [closed]
What is the RMS value of current $i=3+4sin(\omega t+\pi/3)$?
Please give step by step solution.
0
votes
3answers
307 views
charge density in a wire
if we have a infinitely thin and infinitely long straight wire on the z-Axis with given current I(t), how can i compute the charge density?
I figured out that the current-density is given by ...
4
votes
2answers
217 views
How can I cause a levitating magnet to rotate?
I have a device like this one:
http://www.youtube.com/watch?v=kA_hw_lY-OY (All of them work the same)
Here's an image:
I want to make it spin without touching it with hands.
I tried using magnets ...
4
votes
2answers
351 views
How to calculate required current and specifications for a “wet coil” to generate x Tesla of magnetic field?
A water management project requires a "wet coil" (coil will be submerged in aqueous media) designed to generate a steady-state electromagnetic field of adjustable magnetic magnetic flux density at the ...
1
vote
0answers
126 views
If we have a current I flowing down a wire, why must the net bound current be zero?
Say we are dealing with a wire that has a current I flowing through it, i.e. I is the free current. Why must it then hold that the net bound current, that is, the bound volume current, $J_b$, and the ...
1
vote
2answers
742 views
Does the 'mAh' rating of a battery have something to do with its power?
I'm curious about the 'mAh' of a battery: how can this impact the power of the battery?
I've done some research on the internet, and most of the articles I found explain about the 'amount of charge ...
3
votes
2answers
407 views
How do electrons know that?
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?
0
votes
0answers
152 views
How much current needed to cancel Earth's magnetic field [closed]
It can be shown the magnetic field in a long narrow tube that is 5 meters is uniform and given by
$$B=1.26 \times 10^{-6} N I$$
where N is number of wire loops/meter. Assuming the solenoid is aligned ...
2
votes
0answers
80 views
How much current would be generated by polarity reversal of Earth's magnetic field?
Continuing from my previous question Is reversal of magnetic polarity in a planet an instantaneous occurence?
A change in magnetic flux is expected to generate an EMF.
In the case where the ...
0
votes
1answer
272 views
Improvement Of Soft Iron And Steel As Magnets
I am given to know that soft iron is used as temporary electromagnet since it has high permeability i.e. the ability to align its domains corresponding to the electric field around it, however has a ...
