# Read about electricity and magnetism | 93 Discussions | Page 1

1. ### Resultant field at the center of two semicircular current arcs

So the magnetic field induced at the center of a current-carrying loop is given by: B = μ0 i /2r where r is the radius of the loop In the case of a semi-circular loop, this becomes B = μ0 i /4r In the question, i = 2A, r1 = 1m and r2 = 2m So, field induced at the center of first semicircular...
2. ### I Charge Inside a Cavity in a Conductor

Let us say we have a cavity inside a conductor. We then sprinkle some charge with density ##\rho(x,y,z)## inside this surface. We have two equations for the electric field $$\nabla\times\mathbf{E}=0$$ $$\nabla\cdot\mathbf{E}=\frac{\rho}{\epsilon_0}$$ We also have the boundary conditions...
3. ### I How does Electric Field Penetrate through a Multi-Layer Sandwich of different dielectrics?

I'm trying to understand how the total electric field changes as it passes through layers with different electrical permittivities and conductivities (as shown in the linked figure). The rectangular prism layers are assumed to be very thin. The conductivities ##\sigma## and relative...
4. ### Electric field from a charge q1

Hi, I have a charge q1 = -10 * 10^9. The the coordinatesare (3,4)m. I found the electric field vector that is (-2160i -2880j) n/c. My questions is if I add a charge q2 to the the coordinates(0,0) is the electric field stay the same?
5. ### Force on a copper loop entering into a magnetic Field B with speed v

Hi, second problem in one evening, I'm sorry! But i'm also not quite sure if I did this one right. I had thought I need lenz's law but there is no current before entering the field so I just use the induced Voltage? My approach: ## V = \frac {B*A}{t} ## ## IR = \frac {B*A}{t} ## and ## A = v*t...
6. ### What are some good books on electricity and Magnetism

Can someone please suggest some good books on electricity and Magnetism for graduation in physics? Thanks for helping:smile:
7. ### Sphere-with-non-uniform-charge-density ρ= k/r

I am working on the same problem as a previous post, but he already marked it as answered and did not post a solution. https://www.physicsforums.com/threads/sphere-with-non-uniform-charge-density.938117/ I am curious as to a method of finding the ##k## and substituting into the electric...
8. ### Final potential difference of a 2 capacitor system

Homework Statement An isolated parallel-plate capacitor of area ##A_1## with an air gap of length ##s_1## is charged up to a potential difference ##\Delta V_1## A second parallel-plate capacitor, initially uncharged, has an area ##A_2## and a gap of length ##s_2## filled with plastic whose...
9. ### Wire surrounded by a linear dielectric in a uniform E field

Homework Statement We have an uncharged, conducting wire with radius a. We surround it by a linear dielectric material, εr, which goes out to radius b. We place this in an external electric field, Eo. Homework Equations We have electric potential inside (a < s < b) Vinbetween=Acosφ +...
10. ### Calculating the electric potential

Homework Statement We have the cross section of a metal pipe that has been split into four sections. Three of the sections have a constant electric potential, Vo. The fourth section is grounded so electric potential is zero. We are looking for electric potential inside and outside of the pipe...
11. ### Electric field of spherical shell

Homework Statement Consider a spherical shell with uniform charge density ρ. The shell is drawn as a donut with inner (R1) and outer (R2) radii. Let r measure the distance from the center of the spherical shell, what is the electric field at r>R2, R1<r<R2, and r<R1. I am working on the r > R2...
12. ### Calculating total Coulomb force vector ?

Homework Statement Consider a configuration consisting one +q charge ( upper right) and three −q charges, arranged in a square. Side lengths = d. Calculate the total F force vector acting on charge +q. Homework Equations Vector form of culomb’s force F=( kq1q2/r^2) rhat (rhat for unit...
13. ### Infinite chain of alternating charges (+/-)

Homework Statement A crystal is a periodic lattice of positively and negatively charged ions. (a) Consider an infinite one-dimensional crystal of alternating charges +q and −q, separated by distance d...
14. ### Testing Electricity and Magnetism section in GRE Physics

Hi, I am taking GRE Physics this year and I am preparing from Conquering GRE Physics book and I have covered everything in that book on Electricity and Magnetism (yet to study Optics and Waves). My question: How much from Griffith Electrodynamics book do I need to study? Or is the material in...
15. ### Some good physics educators on youtube?

HI! I'm in first year physics right now doing the second part of my course - electricity and electromagnetism, and I'm REALLY struggling. This is mostly due to the fact that other than very basic, grade 11 circuits, I had no base going into electricity for first year physics because my teacher...
16. ### Classical Looking for a textbook of undergrad E&M, for Physics Forum Help that I give

I sometimes post answers to threads people post about E&M. Unfortunately, my Masters in physics was 40 years ago and I am a little rusty. I am looking for something that will help me answer people's questions. The level of math can be fairly sophisticated as I have brushed up a bit.
17. ### I Please suggest whether I should use delta or dx method.

I previously made a derivation of Neumann potential. It can be found in the pdf file below. I originally made it in the ##dx## method. It involved equations like ##dm=I dS##. My maths teacher told that such an expression has no meaning, at least in elementary calculus. However I argued that my...
18. ### I Fun magnetics question with the Meissner Effect

I was hoping I could get some help deriving a formula that shows how much current is needed to generate enough of a magnetic field to lift an X newton mass L meters above a superconductor. ( Probably in centimeters but meters here for the sake of SI easiness ) I was helping one of my professors...
19. ### I What is the electrostatic force field?

I have just covered the electricity unit in my advanced higher physics course, and have happily accepted that a force is created between charged particles. I understand that coulombs law can be used to calculate this force, but here is my question. What actually is this force between the charged...
20. ### Radial force on charged particle in beam of positive ions

Homework Statement Many experiments in physics call for a beam of charged particles. The stability and “optics” of charged-particle beams are influenced by the electric and magnetic forces that the individual charged particles in the beam exert on one another. Consider a beam of positively...
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### Resistors in Series - Lab data confusion

Homework Statement (see my attached photo to better understand where I am coming from!) So after some research, I've discovered that the current at different points in a simple series circuit is supposed to be the same value, and that the voltage is supposed to be different values. I...
22. S

### Resistors in Series - Lab data confusion

Hi guys! (see my attached photo to better understand where I am coming from!) So after some research, I've discovered that the current at different points in a simple series circuit is supposed to be the same value, and that the voltage is supposed to be different values. I performed a lab on...
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### I Is average time between and after collision same for a gas?

I am stuck on this concept in my physics book where the author claims that in a low density ionic gas the average of the time between collision and average of the time taken from last collision in ions is same. He further states that the average time to the next collision is same as the average...
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### Draw field lines for both magnetic fields

Homework Statement Homework Equations N/A 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 the...
25. ### Electric Field and Potential Scenario

Homework Statement I was wondering in what situation would the potential and the electric field of the system both be equal to zero at the same time? Homework Equations W=-ΔU=-ΔVq ΔV=-∫Edr V=kQ/r (with reference r->∞) The Attempt at a Solution I know for the middle of a dipole the potential...
26. ### I Not sure what I can make into equivalent resistors

Could I combine the two resistors together in parallel to make an equivalent resistor, and then use that equivalent resistor in series with the capacitor? It would be great if there was some rule of thumb that I can use to know what I can make into an equivalent resistor/capacitor down the line...

30. ### A Discontinuities in the time derivative of the magnetic field

An inductor and resistor are arranged in parallel to a constant voltage source. There is a switch connected to a terminal on the inductor that can create a closed loop that includes either the voltage source, or the resistor. The switch is left connecting the source and inductor for a long...