# What is Electromagnatics: Definition and 15 Discussions

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1. ### B Untraditional Space Travel

If an infinite amount of energy were available to create the lift mechanism for a space launch. What would be required to fire a 200lb object into low Earth orbit(160km) after speeding it up in a way similar to how the large hadron collider speeds up a particle. Assuming the launch vehicle...
2. ### What is the attenuation below cut-off frequency for TE10?

It is not useful to talk about the attenuation below cut-off frequency, but I have this doubt about what happens to the wave below cut off for an electric conductor. As we know if we derive the propagation constant, it becomes imaginary saying that there should not be any wave propagating in the...
3. ### Inductrack and Halbach Array

Hi, I am currently completing a Gold CREST Award on the Hyperloop Train, and when researching came across a technolofgy called Inductrack. I kind of understand the general concept behind it, however, there's this one paragraph I'm not too sure on and was wondering if someone could explain it...
4. ### Magnetic field and potential

Homework Statement Homework EquationsThe Attempt at a Solution Using ## \nabla \times \vec A = \vec B##. I got that both ##\v A_1 ~~and~~ \vec A_2 ## produce ## \vec B##. So, the correct option is (d). Is this correct? [/B]
5. A

### Why is del(E_t) zero in TEM mode of transmission lines?

I was going through MIT opencourseware https://ocw.mit.edu/courses/electrical-engineering-and-computer-science/6-013-electromagnetics-and-applications-spring-2009/readings/MIT6_013S09_chap07.pdf and I didnt understand exactly why in equation 7.1.37 and 7.1.38 in page 192 the divergence of...
6. ### Surface current density-logic and definition contradict

Okay, so in Griffith's introduction to electrodynamics, Griffith clearly defines surface current density as follows: "when charge flows over a surface, we describe it by the surface current density, K. Consider a 'ribbon' of infinitesimal width dL running parallel to the current flow. If the...
7. ### Maximizing x-component of force

A charge Q is placed at a distance a = 3m and a charge q is placed at a distance b For what value(s) of b is the x-component of the force maximized? I know to maximize the force we need to maximize F_Qq = k Qq b/(3^2 + b^2)^{3/2}. To do this we need to set the first derivative to zero and...
8. ### [Physics 2 w/calc Uni] Cylinder inside of a cylindrical shell

Figure (a) shows a narrow charged solid cylinder that is coaxial with a larger charged cylindrical shell. Both are nonconducting and thin and have uniform surface charge densities on their outer surfaces. Figure (b) gives the radial component E of the electric field versus radial distance r from...
9. ### 2 Types Of Magnetic Potential Energy

There are 2 types of magnetic potential energy equations: 1. ##U = -\vec \mu \cdot \vec B## 2. ##U = \frac{1}{2} \int \mathbf{A} \cdot \mathbf{J} \, \mathrm{d}V## - I have searched for the second equation, only can find some information in one web site. Do you know what their names are and...
10. ### What is the equivalent of Electric P.E. in Magnetism?

There is an analogy between electric and gravitational potential energy. ## U_g = \frac {GmM}{r}## ## U_e = \frac {kqQ}{r}## What is the analogous formula in magnetostatics? Thanks...
11. ### How did Maxwell's theory predict that c is constant?

In the book, briefer history of time, hawking says that maxwell's theory of electromagnetism, concluded that speed of light is finite and constant, which made other physicists to give up the idea of absolute time, and think of newer concepts. How did maxwell, through his theories, correctly said...
12. ### Relativity and Circular Magnetic Field

According to relativity, If magnetic field is just an electric field viewed from a different frame of reference, why is the magnetic field around the wire is circular?
13. ### Two Velocities in the Lorentz Law

Lorentz Force: $$\vec{F}=q\vec{v_1}\times\vec{B}$$ v1 is the velocity of particle. And magnetic field is: $$\vec{B}=\frac{\mu_0}{4\pi}\vec{v_2}\times\frac{\hat{r}}{r^2}$$ If we combine them, we see that there are 2 velocities: v1 and v2... I just watched this video about relativity and...
14. ### Photonic local density of states and field intensity

Dear All: I'm very confusing with the relationship between photonic local density of states and the field intensity. In thermal equilibrium, the field intensity should be proportional to the photon's number (or squared) and also be proportional to the local density of states. We know that this...
15. ### Electromagnatics Disperate Help

Hi i am in ap physics and we just finished the electric charges and electric fields chapter but i am completely clueless. I haven't been keeping up with the problems and haven't been to a lot of classes and now it has come back to haunt me. Any good sites out there or can anyone answer some of...