All Questions
28
questions
1
vote
1
answer
54
views
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) \...
- 29
0
votes
1
answer
32
views
How can equilibrium state be considered even if body is an accelerated motion?
This is a question from Irodov:
Two small equally charged spheres, each of mass $m$ are suspended from the same point silk threads length $l$. The distance between the spheres $x\ll l$. Find the rate ...
0
votes
3
answers
492
views
Using Binomial and Taylor Expansions to Demonstrate Harmonic Motion [closed]
I'm doing a physics 2 self-study and I came across this question in my textbook:
A ball of mass m and charge q is constrained to move along the y axis. At the origin is a stationary charge Q. The ...
- 1
1
vote
2
answers
50
views
Equation for a rotating loop with one fixed end [closed]
This loop is rotating with angular speed $\omega$ in the counterclockwise direction in a magnetic field. I need to find the differential area element (for the purpose of finding flux). Is it going to ...
- 11
-3
votes
2
answers
169
views
Can someone explain why the moment of inertia of a circular current carrying loop is $\frac12 mr^2$? [closed]
Can someone explain why the moment of inertia of this circular current carrying ring about its diameter is $\frac12 mr^2$?
- 63
0
votes
1
answer
319
views
How come the Biot–Savart law is not applicable to derivation of magnetic field around an infinitely long, straight wire? [closed]
Context
[Edited Nov 20, 2021]
When the present question was initially asked, there was a derivation presented that lead to the wrong result. The Biot–Savart integral that I used to write the magnetic ...
- 460
0
votes
2
answers
99
views
Lorentz Force and Circular motion - What is the magnetic field causing the movement? [closed]
I am given this problem:
A particle with mass $m$ and positive charge $q$ is moving in the following path on the $x$-$y$ plane. It's path consists of semicircles as shown below. The particle's ...
-3
votes
1
answer
43
views
Problem on mechanics of bodies [closed]
I am trying to solve this problem
I thought using archimidis principle would be a way. the second body has more cavity than the first body(left body), i think, given that the 1st body will ...
- 31
3
votes
2
answers
2k
views
How to find the equation of motion of a particle in an electric and magnetic field? [closed]
I'm trying to solve a homework problem. The statement of the problem says:
"When the negatively charged plate of a parallel plate capacitor is lit up by light of a certain wavelength, electrons are ...
- 207
1
vote
1
answer
674
views
Charged particle moving in magnetic field using cylindrical coordinate [closed]
It's knowen that a charged particle take a helix trajectory in a uniform magnetic field $B =B e_z$
I tried to study this problem using cylindrical coordinate and i get that
$$F=q v ×B = m a$$
in ...
- 257
1
vote
2
answers
236
views
Non-relativistic limit of a particle in the uniform electric field
For this problem, the solution is:
$$y=\frac{m}{qE}\gamma\left[\cosh\left(\frac{qEx}{mv\gamma}\right)-1\right]$$
where $\gamma = 1/\sqrt{1-v^2}$. Here something seems to be wrong. I think that for the ...
- 1,669
1
vote
2
answers
703
views
How to calculate Centripetal force of a helical movement inside a magnetic field?
I have recently studied about the movement of a particle in a basic electromagnetic field. It circulates perpendicular to the field lines.
And the equation is then, $F= Bqv$
$B$ is the value of the ...
- 189
2
votes
3
answers
205
views
Prove a force driven by a cross product between a vector and its velocity gives a spiral movement parallel to the vector
I was given a problem in a Classical Mechanics course that went somehow like the following:
"Consider a particle of mass $m$ moving under the presence of a force $\vec{F} = k\hat{x}\times\vec{v}$, ...
- 382
0
votes
1
answer
40
views
Particle with constant momenta? [closed]
Consider a particle of mass $m$ subjected to the following potential,
$$
\vec{A}=\frac{1}{2}(\vec{B}\times\vec{r})
$$
Where the magnetic field $\vec{B}$ is constant.
Can someone prove that $\dot{...
- 297
0
votes
1
answer
77
views
Why can you equal $e\times U=\frac12 mv^2$? [closed]
When calculating the accelerating voltage to accelerate an electron to a certain speed, we usually use the following equation:
$$e\times U = \frac{1}{2}mv^2$$
But why does this work? On the left ...
- 13
0
votes
1
answer
140
views
How do I show that the total energy of a particle moving in an electrostatic field is constant?
Basically the Lorentz force says that:
$$F=qE+qv × B$$
I am asked to show that if a particle moves in an electrostatic field
$$E= - ∇V(x,y,z)$$
and ANY magnetic field, then the energy:
$$\frac{1}{...
0
votes
2
answers
10k
views
Electromagnet Electricity Consumption?
Wikipedia states that -
The only power consumed in a DC electromagnet is due to the resistance of the windings, and is dissipated as heat.
Is this true? So powerful magnets like junkyard magnets ...
- 251
6
votes
3
answers
1k
views
What would it take to cause lightning to jump between the Moon and the Earth?
This question comes from @Floris' speculation at the end of his excellent answer about what it would take to kill everyone on the Earth with electricity.
Doing all this in 1/10th of a second requires ...
- 4,534
2
votes
0
answers
492
views
Motion of a charged particle in a "solid" charged sphere (accounting for radiation)
Consider a particle (point charge) with charge $q$ and mass $m$ that crosses into a uniformly charged sphere (with charge $Q$ and radius $R$). The trajectory of the particle is a diameter of the ...
- 31
0
votes
3
answers
148
views
Traveling to Mars in 24 Days
I am trying to calculate an electromagnetic rail launch from the Moon but I need to know if humans can survive the launch. Please see the specs below.
150 miles of track
Proposed final launch speed ...
- 13
0
votes
1
answer
2k
views
Equation of Trajectory [closed]
I was reading about Lorentz force law and motion of a charged particle under Electric field or magnetic field and I understood how they move in it.
But as I was moving further I came across the ...
- 343
1
vote
2
answers
423
views
Description of the motion of the COM of a system of charged particles moving in a magnetic field
I recently came across a problem where an electrically neutral particle is at rest in a uniform magnetic field. The particle now splits into two charged particles of equal mass $m$; charge and mass ...
- 2,077
0
votes
2
answers
610
views
Electrical force between two objects
I tried to solve the following problem:
There are 2 objects . The object m1 with charge q and the object m2 with charge q.(same charge).The object m2 is connected with a rope to the ceiling.
at the ...
- 397
9
votes
1
answer
860
views
Electron in the proximity of a magnetic monopole
I am puzzling about an exercise in the book "Electromagnetic Theory" by Ferraro (p.543).
An electron (mass $m$, charge $-e$) in a monopole magnetic field $\vec{B}\left(\vec{r}\right)=g\frac{\vec{r}}{...
- 393
0
votes
1
answer
6k
views
A basic question: what is accelerating voltage? [closed]
Or would it be acceleration voltage? Acceleration sounds like it makes more sense, but my paper says accelerating.
What are possible ways you could go about calculating it?
- 103
1
vote
2
answers
789
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 ...
- 2,565