Tagged Questions
0
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0answers
17 views
electrostatic repulsion [closed]
Consider a homogeneous ring of radius $R$ made of a thin wire of cross section $A$ with $R^2≫A$. A charge $Q_1=10\mu C$, uniformly distributed over the ring, broke it apart due to electrostatic ...
0
votes
1answer
21 views
Doubt in problem regarding resistance a of cylinder
I've been working on some exercises and I'm in doubt if my procedure with this one is correct. We have a hollow cylinder with internal radius $r_a$, external radius $r_b$, resistivity $\rho$ and ...
1
vote
0answers
25 views
Induced current using a reference system bound with a moving charge
Let's suppose to have a charge moving at velocity $\textbf{v}$ and a square wire.
If I choose a reference system bound with the square wire, since the charge is moving at velocity $\textbf{v}$, in ...
0
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0answers
27 views
Magnetic Field on a particle between two Helmholtz Coils
Given a Helmholtz coil of radius $R$ and with a current $I$, and assuming the coil is a circle centered at the origin in the $xy$-plane, what is the magnetic field on a particle at the point $(a, b, ...
1
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0answers
27 views
Power transfer in a transformer
Can it be proved using the concept of induced emf that power supplied at the primary coil equals power consumed at the secondary. I tried following. Let primary coil be called 1 and secondary be ...
3
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3answers
165 views
Energy conserved… or not? Confused!
I am confused. Could someone kindly explain what's going on in this question?
A particle of mass $m$ and charge $e$ moves in the $x,y-$ plane. There is a constant magnetic field $B$ that points in ...
0
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0answers
35 views
Magnetic Field Lines predict? [closed]
Question: Magnetic field lines determine:
(A) only the direction of the field
(B) the relative strength of the field
(C) both the relative strength and the detection of the field
(D) only the ...
0
votes
0answers
32 views
Lagrangian of electromagnetic tensor in light cone coordinates? [closed]
I have Lagrangian Density of Electromagnetic field Tensor in light cone coordinates using D'Alembertian operator and Lagrangian density in Cartesian coordinates. I couldn't figure out the way to ...
0
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0answers
66 views
The electric field inside a uniformly polarized cylinder
Given a uniformly polarized cylinder with some polarization $P\vec{z}$ which has radius $R \gg d$ where $d$ is the height and $R$ is the radius. The cylinder's center is on $\vec{z}$ and it's on the ...
0
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0answers
54 views
The gauge-invariance of the probability current
It is simple to show that under the gauge transformation $$\begin{cases}\vec A\to\vec A+\nabla\chi\\
\phi\to\phi-\frac{\partial \chi}{\partial t}\\
\psi\to \psi ...
3
votes
1answer
38 views
inductance value of a single turn thin circular coil
the question may seem simple but I haven't found any fitting formula yet. The problem is the following:
consider a single-turn, circular coil made of reasonably thin wire (diameter of the wire much ...
4
votes
2answers
109 views
Vector potential
I have difficulty understanding the following vector calculus example. Text can be found here. It is the 5th Q&A -- starting with equation (31.1035).It concerns finding the vector potential of a ...
0
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2answers
44 views
Electrical force as a replacement for Gravitational force [closed]
Suppose the force between the Earth and Moon were electrical instead of gravitational, with the Earth having a positive charge and the Moon having a negative one. If the magnitude of each charge ...
2
votes
1answer
101 views
Induced Current, Dipole Falling Under Gravity Towards Circular Loop [closed]
Suppose a magnetic dipole $\mathbf{m} = m \hat{z}$ is falling towards a circular loop of radius $b$ under gravity. Assuming the dipole always stays along the $z$-axis of the loop, determine the ...
0
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0answers
35 views
Finding the magnetic dipole moment [closed]
I have been stuck on this question for awhile and it should be really easy.
The relative permeability of cobalt is $u_r = 600$ and the density of atoms is $N_e = 9.02*10^{18} [m^{-3}]$, calculate the ...
0
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0answers
36 views
Magnetic field of a Ferromagnetic cylinder [closed]
I have been stuck on this problem for hours and have no idea how to go about this problem.
You have an infinitely long cylinder made of linear ferromagnetic material of relative permeability Km, ...
1
vote
1answer
43 views
Induced voltage by a rotating ring
Two concentric rings dielectrics and uniformly charged are suspended on the same floor.
The outer ring has a radius R and mass M,
while the other has radius r << R and mass M.
The outer ring ...
0
votes
0answers
44 views
The electrical field of a conductive sphere containing a charge - gounded vs not grounded
Let's suppose we have a sphere but unlike theoretical ones it'll has have some thickness say $\Delta r$ and inner radius $R$. What I was wondering about is how will it behave if we place some charge ...
0
votes
1answer
81 views
How to design a AC/DC generator and motor? [closed]
Through electrodynamics mechanics learning, it is possible to design a simple and elegant design for the following four machines:
1. AC generator
2. AC motor
3. DC generator
4. DC motor
I have some ...
0
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0answers
35 views
Solution of Maxwell's equation for simple, time-harmonic wire
I would like to compute the electric field $\boldsymbol{E}$ in the time-harmonic case for a (thick) wire parallel to the $z$-axis, but I can't quite get to it.
What I've got so far:
The current ...
1
vote
1answer
65 views
Movement of the particle in a magnetic field
This is the numerical question.
A particle having a mass of 0.05 mg carries a charge of $5\times10^{-6}C$. The particle is given an initial horizontal velocity of 5000 m/s, what is the magnitude ...
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0answers
52 views
Could anyone help me to interpret the wave geometrically? [closed]
This is the problem:
A 180-MHz wave travels in medium characterized by $\mu_r = 1$, $\epsilon_r = 25$, and $\sigma = 2.5$ mS/m. The electric field intensity is given by $\widetilde{E} = ...
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0answers
81 views
Equation of motion of charged particle under effect of magnetic field
A charged particle with specific charge q/m diverges from the origin [to the first quadrant] by angle X with x axis and with velocity v. To bring the particle back to the x axis, a magnetic field B is ...
0
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1answer
27 views
2 solenoids: emf and frequency
I'm studying a circuit in AC. I use a function generator and set a waveform.
I have a solenoid and I put a small solenoid inner it.
Could you tell me if there is a relation between frequency and emf ...
0
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0answers
23 views
Hitting the target in two different ways [closed]
Electrons are accelerated by an electron gun. As the electrons exit the gun they are deflected by a uniform magnetic field of fixed magnitude $B$ directed into the page. The electrons hit a small ...
0
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0answers
34 views
Can you find the potential between capacitor plates with liquid dielectric in the capacitor's frame? [closed]
A magnetic field B is applied perpendicular to the plates of a capacitor whose parallel plates are separated by d. An electrically neutral liquid of relative dielectric constant k flows between the ...
0
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1answer
54 views
If I have a rectangular loop moving through a magnetic field, which way will it go?
If I have a rectangular loop moving through a magnetic field, which way will it go?
A uniform magnetic field (say it's pointing into the page)
A square/rectangular loop of wire moving into the field ...
0
votes
2answers
253 views
Capacitors and resistor in series and in parallel [closed]
In this circuit, are $R_1$ and $C_1$ in parallel and $C_2$ and $R_2$ in series?
I have think that the currents that flows trought $R_1$ isn't the same that flows trought $C_1$ so, $R_1$ and $C_1$ ...
0
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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 ...
0
votes
1answer
58 views
A ring placed along $y^2 + z^2 = 4$, $x = 0$ carries a uniform charge of $5 \mu\ C/m$. Find $D$ at $P(3,0,0)$ [closed]
A ring placed along $y^2 + z^2 = 4$, $x = 0$ carries a uniform charge of $5 \mu\ C/m$.
Find $D$ at $P(3,0,0)$
How do I solve this using Coulomb's Law? I used $dE=\dfrac{dQ}{4\pi\epsilon_0 ...
0
votes
1answer
49 views
Electric field at a point $P$
Problem
Charge is distributed uniformly over a large square of side $l$, as shown in the figure. The charge per unit area ($C/m^2$) is $\sigma$. Determine the electric field at a point $P$ a ...
1
vote
1answer
50 views
B-field and Magnetic forces, speed of a particle
Let's say I have a particle moving perpendicular to a uniform magnetic field of magnitude $x \ T$, and it moves in circle with a fixed radius. How do I find the speed of this electron? Initially I ...
0
votes
1answer
48 views
Find the voltage between two points [closed]
Given two point charges $+2\text{ nC}$ and $-3\text{ nC}$ are located at the points $P_1$ $(2,2,-1)\text{ m}$ and $P_2$ $(1,-2,1)\text{ m}$, find the Voltage $V_{ab}$ between points $P_a$ ...
0
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0answers
42 views
magnetic field due to circular coil [closed]
A circular coil has 5 turns and another coil has 8 turns.Both the coils havethe same diameter and both the coils are made up of same material with sameradius.Let 'n' be the strength of magnetic ...
2
votes
2answers
158 views
A charged sphere with pulsing radius
Radius increases and decreases periodically (as a pulse).And so does the charges on the surface of sphere.
I can't get what is gonna happen.the EM waves are produced perpendicularly to motion of ...
0
votes
0answers
66 views
An electron has an initial velocity in B and E field [closed]
An electron has an initial velocity of (14.5j + 18.5k) km/s and a constant acceleration of (1.60×1012 m/s2)i in a region in which uniform electric and magnetic fields are present. If B =(400μT)i, find ...
1
vote
1answer
67 views
Derivative of covariant EM tensor
I cannot seem to prove that the derivative of the duel tensor = 0.
$$ \frac{1}{2}\partial_{\alpha}\epsilon^{\alpha \beta \gamma \delta} F_{\gamma \delta} = 0. $$
Writing this out I get (for some ...
0
votes
1answer
60 views
how to find the diameter of this fuse? [closed]
A fuse blows if the current exceeds 1.0 A. It is made of material that melts at a current density
of 620A/cm2. What is the diameter of the wire, assumed to have a circular profile, in the
fuse?
0
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0answers
129 views
What is the current induced in a straight wire when a magnetic field is turned from on to off?
Consider a straight wire which runs along the y-axis. A B-field exists which is uniform and only in the x-direction:
$$\vec{B}=(B(t),0,0)$$
The B-field at time $t_0$ is 'switched off' in ...
1
vote
2answers
102 views
Potential Inside Conducting Cube
A cubical box with sides of length L consists of six metal plates. Five sides of the box { the plates at $x=0, x=L, y=0, y=L, z=0$ - are grounded. The top of the box (at z = L) is made
of a separate ...
0
votes
2answers
359 views
What is the force between two perpendicular wire? [closed]
What is the force between two perpendicular wire carrying current, one to the north and one to the east?
2
votes
1answer
417 views
Magnetic Fields created by Current-Carrying Wires
The drawing shows two perpendicular, long, straight wires, both of which lie in the plane of the paper. The current in each of the wires is I = 5.6 A. What is the force and torque acting on each wire ...
0
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0answers
73 views
Superconductors for sale? [closed]
Does anyone know where I can purchase superconductors for a school presentation? I don't need a whole kit, just the disk itself. Thanks.
0
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0answers
35 views
Charges and Fields [closed]
Three charged particles lie along the x axis of a Cartesian coordinate system. q1 is located at x = 0,
q2 lies at x and q3 lies at x = r. All three charges are positive, but only q2 is free to move. ...
1
vote
1answer
50 views
Regarding Electromagnetic Plane and Maxwell equations
I asked this on the math.stackechange but I was told that it might be a good idea to ask here too since my problem is physics/math! Here is the question:
Hello everybody I am kind of struggling with ...
0
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0answers
79 views
Parallel straight wires [closed]
Two parallel straight wires each have current in the same direction. If I use the force law for a current in a magnetic field, do the wires attract or repel?
Thank you
0
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0answers
36 views
State equations in magnetic systems
Assume there is an isotropic magnetic material in a homogeneous field $\vec{H}$ inside of a long coil. The work done to the material is given by $\delta A = H dM$, where $M$ is the magnetisation of ...
1
vote
1answer
82 views
Thermodynamics and electromagnetic fields
The energy density in an electromagnetic field is given by: $u = (1/2) <\vec{E}^2 + \vec{B}^2>$ where $<,>$ denotes the average over time. In a cavity it holds that $u= u(T) = ...
0
votes
0answers
48 views
Faraday's Pail Experiment [closed]
I have a question regarding Faraday's Pail Experiment. If we place a negative charge -Q at the centre (ie inside the pail), what will be the magnitude and sign of the induced charges that appear on ...
0
votes
1answer
92 views
a metal bar on a pair of conducting rails that carries a current
This is a homework question, and I solved it already, but something bugs me. So the problem is stated as following:
A metal bar of mass M sits on a pair of long horizontal conducting rails separated ...
