# electromagetism

20. ### I Are these instances of identical magnetic fields?

Are both magnetic fields emanated from an electromagnet fed with a current spike from a charge capacitor and a rotating static magnetic feild from permanent magnets instances of time varying fields? The permanent magnet would be attached to perhaps some rotating disc thus passing over a target...
21. ### Force of one distribution of charge on another

1. Homework Statement I need help on solving this exercise : We have a ring of radius = $a$ uniformly charged (total charge = $Q$) and on its axis a segment $OA$ (length = $a$ also) of uniformly distributed positive electric charges with the charge density $\lambda'$ and of total...
22. ### I What was the value of the permeability constant in 1865?

What is the value of the permeability constant in 1865, the time when Maxwell's theory was first published? What was the experimental method used to determine the constant. Who did the experiment.
23. ### Charging a battery by moving a magnet randomly in 2D plane?

I'm sorry if this question is a little abstract, but would appreciate any guidance! It's for a DIY project I am considering. Suppose you have a flat panel mounted on a wall, and a very strong magnet that will move in any direction on the plane of the flat panel. Through any possible arrangement...
24. ### Show that the radiation field is transverse

1. Homework Statement Show that the radiation field is transverse, $\vec{\nabla}\cdot\vec{A}=0$ and obeys the wave equation $\nabla^2\vec{A}-\frac{1}{c^2}\partial_t^2\vec{A}=0$. You should start from the expansion of the quantum Electromagnetic field. 2. Homework Equations...
25. ### Propagation of EM waves

1. Homework Statement Use Maxwell's equations to elaborate an coherent explication of why electromagnetic waves propagate independently of the source that produces them. 2. Homework Equations Maxwell's equations in vacuum: $\nabla * E=0$ $\nabla * B=0$ ##\nabla \times E =...
26. ### Toroid with Air Gap magnetostatics problem

1. Homework Statement consider a toroidal electromagnet with an iron ring threaded through the turns of wire. The ring is not complete and has a narrow parallel-sided air gap of thickness d. The iron has a constant magnetization of magnitude M in the azimuthal direction. Use Ampere's law in...
27. ### Winding Direction Consideration (Proper Winding)

Hello, I'm boy who suddenly been strucked by curiosity on how hand crank generator works and i watch and read some of how to create one, specially this one on youtube: and i want to create one but i don't have a 3D printer, but i saw some alternative but as i do/design my own coil based on...
28. ### I Inverse square law confusion

i have heard how our broadcasts will be seen by aliens far away or whatever. but i realize those signals are going to "attenuate" by d^-2 anyway... how come in astronomy we can see light sources millions of light years away? shouldn't those signals be far too weak to detect after such a long...
29. ### Is today's exam question unsolvable? - Proton Motion in a Magnetic Field

<Moderator's note: Moved from a technical forum and thus no template.> Hello all, Earlier today I had an electromagnetism exam, and it seems to me that this problem is unsolvable. There's just too little information given. A proton enters an uniform magnetic field. It's initial speed v is...
30. ### Courses Review Griffiths E/M before Jackson?

Hello, I will be starting my junior year this August, I shall be having the dreaded advanced electromagnetism course that follows Jackson's book the coming semester. Unfortunately, I didn't work very hard during my freshman year e/m course (which uses Griffiths' book) and have a few gaps in my...