All Questions
Tagged with electromagnetism homework-and-exercises
1,550
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Magnetic field in the left focus of an ellipse current loop
given a 2D ellipse in 3D space parametrized as $x(t)=a\cos{t}$, $y(t)=b\sin{t}$, I would like to find the magnetic field at point $(-c,0,0)$, $c=\sqrt{a^2-b^2}$. (The current $I$ is running counter-...
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Why In the following $RL$ circuit, the connection to $b$ must actually be made an instant before the connection to $a$ Is broken? [duplicate]
In Resnick halliday, student 10th edition page - 795. In the topic current decay in RL circuit, the following statement is used, the connection to b must actually be made an instant before the ...
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Electric field is produced by the changing magnetic field and not by charged particles according to coulomb's law or Gauss's law?
In my physics textbook, Concept of physics by H.C. Verma, in the section on "Induced electric field", the statement below is written (p. 291):
Electric field is produced by the changing ...
user363762
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Is the strength of the charge equal on all points on an equipotential surface? [closed]
Since the equipotential is calculated by $V = q\cdot \frac{k}{r}$ I suppose that the charge is the same at any point on an equipotential surface but I'm not sure.
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What exactly is induced electric field, Is it present only in conducting loops? [duplicate]
In my textbook it is written that : The presence of a conducting loop is not necessary to have an induced electric field. As long as $\vec B$ keeps changing, the electric field is present. If a loop ...
user376280
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2
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Vector potential of axisymmetric electromagnetic field [closed]
Consider an axisymmetric electromagnetic field. Using cylindrical coordinates $(r,\theta, z)$, where the axis of symmetry is the $z$-axis, let the radial component of the vector potential $A$ be $A_r$ ...
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Help deriving Maxwell's equations from the Lagrangian [duplicate]
Starting with the Lagrangian density $$\mathcal{L} = -\frac{1}{2}(\partial_\mu \mathcal{A}_\nu)(\partial^\mu \mathcal{A}^\nu)+\frac{1}{2}(\partial_\mu \mathcal{A}^\mu)^2,$$ I don't understand how to ...
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What is the force between two charges moving at 0.5c relative to each other? [closed]
Suppose two charges, $q_{1}$ and $q_{2}$ are in uniform translational motion relative to each other. If the relativity velocity is relativistic, e.g. $0.5c$, how can the force between the two charges ...
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Confusion on Lorentz Factor for a line charge density
The question is from Griffith's Introduction to Electrodynamics, the chapter on Special Relativity:
A stationary magnetic dipole, $\vec m = m\hat z$, is situated above an infinite
uniform surface ...
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Calculating Magnetic Vector&Scalar Potential
I want to calculate the magnetic scalar and vector potentials for an infinite axial current density given as
\begin{equation}
J(r,\varphi) = \frac{I}{R} \delta(r-R) \sin\varphi \cos\varphi \bf{\hat{k}...
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Where does force act in two parallel current carrying conductors?
F=ILB.so consider length as 5 m and I as 2 ampere and B as 5 T.so the force is 50 N.does this 50 N act at one point or equally applied on full length like pressure.So what does force/length in this ...
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Point charge between two infinite dielectrics [closed]
Two infinite linear homogeneous and isotropic dielectrics $\epsilon_1$ , $\epsilon_2$, occupy the regions $z>0$ , $z<0$ respectively. A point charge q is located at the origin. By applying the ...
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Purcell/Morin: Why is approximating the resistance of a tapered rod using disk slices in series not adequate when the taper occurs very quickly?
The following exposition and question are based on two problems from the book "Electricity and Magnetism" by Purcell and Morin (problems 4.32 and 4.6 from Chapter 4 called "Electric ...
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What is the expression for current density of a ring in spherical coordinates [closed]
I am not understanding the following expression for the current density of a ring of radius $a$ : $$J_{\phi}= I \sin\theta'\delta (\cos\theta')\delta(r'-a)/a.$$ It is dimensionally correct. I do not ...
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Prove that the electrostatic potential is zero (Wald) [closed]
Let $V$ be a bounded region of space and let $\phi $ be an electrostatic potential that is source free in this region, so that $\nabla^2 \phi=0$ throughout $V$. Suppose that $x$ is lying on the ...
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Why does $\vec v \times \vec B$ change to $\vec a \cdot \vec B$? [closed]
I was doing a question where the solution said this:
$$\vec F = q (\vec v \times \vec B)$$
$$m \vec a= q (\vec v \times \vec B)$$
$$ \therefore \vec a \cdot \vec B = 0 $$
$$(x\hat i + 7 \hat j) \...
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Why does a circular loop in an external magnetic field when released flip over?
A current-carrying loop of wire is placed in a uniform external magnetic field as shown. If the current in the wire is traveling counterclockwise in the picture, what do you predict the loop will do ...
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Propagation delay from moving magnetic field [closed]
If you have a magnet moving according to some velocity with a given magnetic field how do you compute the field at a given time given the propagation delay?
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Trying to find the magnetic force applied by an infinite wire on a circuit both carrying different currents
The problem I'm trying to solve is:
We have:
An infinite wire carrying the current I and creating the magnetic field: $\vec{B}(M) = \frac{\mu_0I}{2\pi\rho}\vec{e}_{\phi}$
A square shaped loop ...
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Force exerted by the southern hemisphere of a uniformly charged sphere on the northern hemisphere
I understand that this question has been asked multiple times before but my question is regarding something specific.
I came across the following solution on the web:
Since $\vec{E}$ is the field at ...
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EMF vs time graph for a coil moving into and out of a magnetic field
Here is the context:
Here is the answer key:
Please see the images attached. Why does the emf graph have curves on it? What is causing the induced emf to change as it enters the magnetic field, and ...
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Current density in the presence of a stationary point charge of varying magnitude
I have been trying to solve the following problem out of Modern Electrodynamics by Andrew Zangwill (Problem 20.8):
A charge density $\rho(\vec{r},t) = q(t)\delta(r) $ where $ q(t) = 0$ for $t < 0$ ...
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How to derive the magnetic field at a point a distance $x$ from the center of the axis of a circular loop of radius $R$ carrying current $I$? [closed]
Question: What is the magnetic field at a point a distance $x$ from the center of the axis of a circular loop of radius $R$ carrying current $I$?
I was given the answer $\frac{\mu_0}2 \frac{IR^2}{(x^...
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Why is west side wing at higher potential? [closed]
A Boeing 747 with a wingspan of 64.4 m is flying in this area due north at 275 m/s. The earth's magnetic field at the plane’s location has a magnitude of 52.5 µT. Although it points north, it is ...
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Drift velocity current electricity [closed]
I have a question which I got stumbled upon between two different options (MCQ), as it required to have only one correct option. So the question goes like this:
In a metallic conductor, under the ...
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Help with forming a dimensionless combination proportional to $e^2$ [closed]
I am currently working on a physics problem that asks me to form a dimensionless combination of the fundamental constants $e=\left|q_e\right|$, $\hbar$, $c$, and $\epsilon_0$ that is proportional to $...
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Finding the equation of motion for vector potential $A_{\mu}$ in topologically massive electrodynamics
Essentially I want to vary the action
$$
S_M = \int d^3x \sqrt{-g} \left[- \frac{1}{4} F^{\mu \nu} F_{\mu \nu} - \frac{\alpha}{2} \epsilon^{\mu \nu \rho} A_\mu F_{\nu \rho} \right]
$$
with respect to $...
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In The question given below, why the length for calculating reluctance is taken by those dotted lines?
The question is as follows:
For the core shown in Fig. 3.20, it is required to produce a flux of 2 mWb in the limb CD. The entire core has a rectangular cross section of 2cm × 2cm. The magnetizing ...
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Physics HL IB 2008: Transformer currents question
A question on the IB HL Physics paper of a couple of years back looks like this:
In the second image, taken from this video solution, you see that the given answer should be D.
Now, I have an issue ...
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Confusion regarding magnetic length
Consider the geometric length of a magnet to be $L$ and magnetic length to be $L'$.
Some sources claim that $L'$ = $(0.84)L$.
One such claim can be found here:-
I cannot find any good reason to be ...
user355398