# Tagged Questions

2answers
70 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 ...
2answers
86 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 ...
1answer
67 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 ...
4answers
59 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 ...
3answers
171 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 ...
2answers
77 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 ...
1answer
43 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 ...
1answer
38 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 ...
0answers
39 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 ...
1answer
112 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 ...
4answers
104 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 ...
1answer
59 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?
0answers
43 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 ...
2answers
103 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 ...
0answers
141 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.
3answers
290 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 ...
2answers
188 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 ...
2answers
312 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 ...
0answers
121 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 ...
2answers
619 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 ...
2answers
383 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?
0answers
139 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 ...
0answers
76 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 ...
1answer
246 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 ...
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