# electromagentic

1. ### A Time derivative jump of the electric/magnetic field

So I just wanted to see if anyone could offer some suggestions. So in my mind this seems impossible, in the case of electric field a jump in time derivative of that field would indicated in my mind that electric charge was either introduced or removed from the system instantaneously which would...
2. ### Circular loop of wire is concentric with a solenoid

Question: In Figure (a), a circular loop of wire is concentric with a solenoid and lies in a plane perpendicular to the solenoid's central axis.The loop has radius 6.13 cm. The solenoid has radius 2.07 cm, consists of 8230 turns/m, and has a current i_sol varying with time t as given in Figure...
3. ### Fringe spacing of the Interference pattern due to two Coherent waves

Homework Statement: In the attached image. Homework Equations: formulas of fringe width and phase differences I think. It has been a long time since I have dealt with these kinds of interference/fringewidth problem, I cant figure out a way to start solving this problem. I was thinking about...
4. ### Number of Turns vs. Wire Gauge (BLDC Motor)

Summary: For the same mass of copper wire, would more turns or greater thickness create a stronger magnetic field from a coil? So I am attempting to make a brush less DC motor, and I am wondering whether the coils would create a greater magnetic force if there are more turns or if the wire is...
5. ### I Lorentz gauge

hi, I'm currently taking a classical field theory class (electromagnetism in the language of tensors and actions and etc) and we have just encountered the gauge symmetry, that is for the 4 vector potential we can add a gradient of some smooth function and get the same physics (if we take Aμ →...
6. ### Polarization dependent phase shift of EM waves on reflection off of a dense medium

I've seen this video: There it is explained that an electromagnetic (here radio) wave has a phase shift if it was radiated in horizontal polarization, but it does not experience the phase shift when it was emitted vertically polarized when it gets reflected on the ground. When reading up on...
7. ### I Particle movement in a non-static magnetic field

Particles follows accordingly the general equation: $$m*\overrightarrow{a}=q*\overrightarrow{E}+q*\overrightarrow{v}\wedge \overrightarrow{B}$$ But in the case of two coupled coils the time varying current at primary coil (and its magnetic field variation) creates corresponding varying...
8. ### Getting very low flux linkage in ANSYS Maxwell

I'm new to ANSYS Maxwell and I'm trying to follow the inductance calculation example in the user's guide. The results for the inductance are pretty close but the value of flux are very low. What cause this? What should I do?
9. ### Calculate the power measured by the detector at distance h from the source

1. Homework Statement An isotropic point source radiates electromagnetic energy, and its output is measured by a thin disc-like detector of radius R. Calculate the power measured by the detector at distance h from the source, assuming that the plane of the disc is orthogonal to the line of...
10. ### How do transformers work, and how to read dot notation

<Moderator's note: Moved from a technical forum and thus no template.> Hi all, I have attempted this question but have a few queries on how transformers work, and what the dot notation represents. (a) The flux would be clockwise around the iron core. (b) This is the question where it gets a...
11. ### Are longitudinal magnetic waves possible?

1. Homework Statement Are longitudinal magnetic waves possible? Give reasons for your answer. 2. Homework Equations Working with Maxwell's equations, Lorentz force, electrostatic and electromagnetic waves in plasma. 3. The Attempt at a Solution No idea whatsoever. I believe it is...
12. ### I One dimensional wave, function of a wave

I am currently reading through 'Optics' by Eugene Hecht chp 2 page 20, he talks about the function of the wave and the direction of travel of the wave i.e $\psi(x)=f(x-t)$ and right at the bottom of the page he say this: Equation (2.5) is often expressed equivalently as some function of ##t -...
13. ### B Waves and Penetration

Why do radio waves pass through walls while visible light can't? I guess this has something to do wit the wavelength. What I know is that higher wavelength means higher ability of penetration. So why radio waves penetrate obstacles?
14. ### The height of a dielectric material between two coaxial pipes

1. Homework Statement This is the exercise 10.6 from Feynman lectures on Physics 2. Two coaxial pipes of radii a and b(a<b) are lowered vertically into an oil bath. If a voltage V is applied between the pipes, show that the oil rises a height H. Show that H=(V^2)(κ-1)ε_0/[ln(b/a)ρ(b^2-a^2)g]...
15. ### Calculation of Change in Magnetic Flux Linkage Across a Wire

1. Homework Statement A straight wire of length 0.20m moves at a steady speed of 3.0m/s at right angles to a magnetic filed of flux density 0.10T. Use Faraday's law to determine the e.m.f. induced across the ends of a wire. 2. Homework Equations E= Nd Φ/dt but N=1 so E= dΦ/dt 3. The Attempt...
16. ### I Duration of electromagnetic disturbance

Let us say I have a moving charge. At each point x,y,z in it's path from understanding there is a transverse electromagnetic wave being radiated (could also be viewed as a photon). The electric field at any point x1,y1,z1 in the path is disturbed. The moving charge does the same thing all...
17. ### Radar Cross section Vs Reflection Coefficient

I am working on HFSS and designing Antennas for LOW RCS , in all previous works they calculate the S11 parameter for the unit cell then make an array form this unit cell and calculate the RCS , my question is what is the relation between S11 and RCS and why we calculate S11 for the unit...
18. ### I Why is there interference if EM waves don't interact?

Radio waves pass through everywhere without interacting with each other and that enables us to hear different phone calls and radios without disturbance. However, we do hear some noise sometimes because different signals interfere with each other. How are both of the last two statements true (if...
19. ### Sign of the Faraday-Lenz equation

1. Homework Statement Hello, good afternoon, I have a question that's coming up when I'm doing electromagnetic induction exercises. In some exercises they ask me to determine the electromotive force (iee), and when they do the exercise resolution they do it with absolute value. In other...
20. ### Simulating a Faraday Cage

Hi guys, I'm wanting to simulate faraday cage form, analysing mesh perforations defined by wavelengths of different electromagnetic spectra (eg. radio, microwave, UV etc). Are there any good analysis softwares which I could import a pre-made digital model with these perforations and simulate...
21. ### Spherical conductor shell problem

1. Homework Statement Consider a spherical conducting shell with inner radius R2 and outer radius R3, that has other spherical conductor inside it with radius R1 (this one is solid). Initially the 2 spheres are connected by a wire. We put a positive charge Q on the sphere and after some time we...
22. A

### Draw field lines for both magnetic fields

1. Homework Statement 2. Homework Equations N/A 3. The Attempt at a Solution Im not sure if I've done this right because it seems too little for 6 marks. I have arrows coming from the north to the south end for the magnet's magnetic field. I have arrows going counter clockwise around...
23. ### I What is magnetic force generated by planar spiral coil?

Hello everybody, I have a planar spiral coil with wire. I want to move a magnet in vertical direction with the magnetic force generated by coil. I want to know how much impulsion to magnet will be occured on vertical direction. I have been searching for the answer but I am a little bit confused...
24. ### Electromagnetic Problem

1. Homework Statement...
25. ### I Why a conductive shield doesn't block the magnetic field?

Hi While studying the shielded wires, i noticed that the magnetic field of the inner conductor can penetrate the shield conductor (can be calculated in the region 3). However, the boundary condition of the magnetic field at the surface (between dielectric and perfect conductor) of a perfect...
26. ### B Photoelectric effect and atomic excitation

A few quick questions I'd like cleared up: 1) Alkali metals are said to have a really low threshold energy, enough for visible light to cause the photoelectric effect. Does this mean if I aim a flashlight (turned on) at a piece of sodium, I could ionise it? Simply flashing a light over a piece...
27. ### A Experiment design FTL particle though magnetic field

Hi. I was browsing Wikipedia on a topic, went to magnetic bearings, etc etc...ended up on synchrotron radiation then the phrase about how a moving or accelerat/ing/ed particle passing through a magnetic field generates electromagnetic radiation. Then I has a revelation. How to get a particle...
28. ### Solenoid Diagram

1. Homework Statement (http://imagemap-generator.dariodomi.de/uploads/160725_010743_e42ea59f2569dfbV.png [Broken]) 2. Homework Equations No equations or anything. Just need a visual concept understanding (11U Physics) 3. The Attempt at a Solution The solutions say that all compasses...
29. ### Where to place a third charge so it experiences no force

1. Homework Statement A point charge of 5.6 microcoulombs is placed at the origin (x=0) of a coordinate system, and another charge of -1.9 microcouloumbs is placed on the x axis at .29m. Where on the axis can a third charge be placed so that it experiences no charge? q1= 5.6 E-6 q2= -1.9 E-6...
30. ### I Electric and Magnetic Fields, Photons, Charges

I know that magnetic fields create moving charges (an electric current) normal to the plane of the magnetic force lines. I also have heard that magnetic and electric fields create each other in a perpendicular direction to the other (badly worded). Electric currents are moving charges (usually...