# Search results

1. ### Where did the electric constant came from?

Try this link. It looks like a factor to make units match: http://en.wikipedia.org/wiki/Vacuum_permittivity
2. ### Electric field inside a conductor?

For a historical and empirical view look up Faraday Cage or Faraday's Pail. Let the conductor be isolated. The net charge on the surface is neutral. Now bring in a source that generates an E field external to the conductor. The free charge in the conductor moves about in a tiny tiny tiny...
3. ### Speed of electric signal?

I'm not an authority on superconductors, however, I am confident that the scientific community reserves the term "super" for very special cases of conductors, fluids, states of matter, etc. I agree the All About Circuits reference should use the term "perfect conductor" in its description, and...
4. ### Speed of electric signal?

My recollection is about 0.9c for a DC signal (infinite frequency) in a copper conductor, but I don't recall doing an analysis myself. This reference treats the transmission line as a superconductor for analysis, and yields results similar to the concept expressed by xantox (note k is the...
5. ### Magnetic Fields and Work

I regard a field as a mathematical model to predict changes in momentum (force) over distance specified with or without a time delay. These momentum interactions can be of course microscopic or macroscopic and through such interactions we infer the existence of a field and build a model...
6. ### Magnetic Fields and Work

The simple case of the charge changing velocity (accelerating) without colliding with anything is then that of an electron (or proton) moving in a constant circle in a magnetic field at constant velocity vC. It seems to me the conservation of momentum and Newton's Third Law would hold upon...
7. ### Magnetic Fields and Work

My understanding is that in the modern view Conservation of Momentum can be used to derive Newton's Third Law for an isolated system. Momentum p = mv is conserved, then the terms F = dp/dt in a time-derivative of conserved momentum should include action reaction pairs. I haven't studied the...
8. ### Magnetic Fields and Work

Comment on my philosophy. Galileo, who is recognized as a pioneer of empirical methods, said the (untested) ideas of the philosophers gave him a great pain! Now this flies in the face of conventional "wisdom," which regards emotion as playing no part in theoretical science! I have discovered it...
9. ### Potential of electrodes

I use the "paint" program in the Windows accessories folder under the Start menu. The tools are sufficient for making a quick rough sketch with some practice. Use black and white and Save As *.png or *.gif seems to produce a small file size for resource economy. The capacitance of a system...
10. ### Fundamentally, what is an electric field?

The OP asks about the similarities between General Relativity and Electromagnetic waves, so I'm posting this link, which has a number of (apparently informed) papers near the bottom on Gravity and Relativity: http://www.metaresearch.org/home.asp [Broken] I've always wondered how space...
11. ### Potential of electrodes

Sketch attached of my understanding of the question. Choice of ground node is arbitrary. There is an E-field in the gap between the plates which may or may not be a linear function from 0 to 100V.
12. ### Potential of electrodes

As long as a 100V source is connected across the electrodes, the difference in potential is 100V. The definition of potential is the work W required to move a positive test charge q+ from one equipotential surface to another. Where q+ = e is the elemental charge. V2 - V1 = dW/q+ You...
13. ### Fundamentally, what is an electric field?

Interference patterns exist in EM fields. The classic example of particle-wave duality is light (or electrons) passing through a double-slit. http://en.wikipedia.org/wiki/Double-slit_experiment I'm not sure how this applies to gravity or electrostatic field models. I'll think about your...
14. ### Fundamentally, what is an electric field?

My understanding is that the electrostatic field lines must terminate on a region of static charge. This is similar to gravity terminatining on a region with mass, although I am not familiar with the theory of gravity waves (time delay in the influence of gravitational force). The motion of...

My old college physics textbook illustrates the experiment as a cork ball, with positive charge, lowered on a silk thread into a conducting can, with the can sitting atop an isolator stand. Before the cork ball touches the bottom or any part of the can, the inside can surface takes a negative...
16. ### Shouldn't a DC current emit EM waves?

This quote is from the Wiki article link cited by Bob S above. In p-n junctions (diodes, transistors, photodetectors) the charge carriers, which are holes and electrons, are generated via some random process that introduces shot noise. In a good conductor there are always many free...
17. ### Shouldn't a DC current emit EM waves?

In a good conductor (such as copper) there are many free electrons in the conduction band. The discrete energy levels of each electron in a single atom merge into one continuous band of energy in the crystal lattice structure of many atoms, so a band with no discrete energy levels occurs. The...
18. ### Shouldn't a DC current emit EM waves?

According to your wiki link, shot noise only applies when there are a relatively small number of electrons in the flow of current, so that noise becomes a statistically significant factor in the average flow, but this factor diminishes in significance as the magnitude of current flow increases...
19. ### Shouldn't a DC current emit EM waves?

The general question says, Shouldn't a DC current emit EM waves? The simple answer is yes, a static B field is generated by a DC current per Ampere's Law. There is a coupling of the electric current and magnetic field whenever charge flows. If the specific question of detecting each electron...
20. ### Electric Field Strength- variations

Bob S, Typically I would sketch the problem in paint and post if it really needs attention. I found a problem in my Field & Waves book which says a static E field can be shaped by a dielectric lens. I am not sure if a charged parabolic surface provides a focus point for a static E field...
21. ### Charge between two isolated capacitors

Please note my analysis showing q = 0 in the figure at post #16 is incorrect. The charge in the dielectric at a plate surface is always smaller than the opposite charge on the metal plate. Please refer to these two references and/or a good physics/electrostatics textbook for proper analysis...
22. ### Shouldn't a DC current emit EM waves?

There is a simpler model that applies as well to smooth DC flow, Ampere's Law. As the question implies, a DC current in a wire induces a static B field around the wire. The wiki doesn't do a great job explaining it, but here's the link...
23. ### Capacitor thermodynamic non sequitur

It happens to me all the time.
24. ### Capacitor thermodynamic non sequitur

I spoke too soon. Let two capacitors have the same capacitance C and maximum voltage rating V. In each configuration let the terminal voltage be Vt. Series Configuration: Equivalent capacitance: Cs = C/2. Terminal voltage: Vt = 2V. Substutute into (1/2)*Cs*(Vt)^2 = (1/2)*(C/2)*(2V)^2...
25. ### Capacitor thermodynamic non sequitur

Scroll down on this reference and see the equivalent capacitance Ceq: http://www.physics.sjsu.edu/becker/physics51/capacitors.htm In theory both configurations could be used to store the same energy. In practice, if the caps are voltage rated for maximum voltage, then stacking two in...
26. ### Charge between two isolated capacitors

LiteHacker, I had an excellent fields and waves professor 20 years back. Now I need to refresh most of the knowledge ... You need to look also at the properties of a conductor, and how a surface charge is induced while it remains an equipotential surface. There may be a free charge flow...
27. ### Charge between two isolated capacitors

Excellent reference on basic electrostatic field problems and parallel plate capacitor: http://www.ac.wwu.edu/~vawter/PhysicsNet/Topics/ElectricForce/FlatSheet.html [Broken] http://www.ac.wwu.edu/~vawter/PhysicsNet/Topics/Capacitors/ParallCap.html [Broken]
28. ### Electric Field Strength- variations

Bob S. & others: Excellent reference on basic electrostatic field problems and parallel plate capacitor: http://www.ac.wwu.edu/~vawter/PhysicsNet/Topics/ElectricForce/FlatSheet.html [Broken] http://www.ac.wwu.edu/~vawter/PhysicsNet/Topics/Capacitors/ParallCap.html [Broken]
29. ### Electric Field Strength- variations

If the permitivity (dielectric constant) is that of free space, I believe the boundary conditions and integral above would give the constant field of a parallel plate capacitor after applying superposition of the two E fields upon the space between the plates. Of course in a practical capacitor...
30. ### Electric Field Strength- variations

Field and Wave Electromagenetics by David K. Cheng (1985). Boundary Conditions at Conductor / Free Space Interface E = \frac{\rho_{s}}{\epsilon_{0}} "The normal component of the E field at a conductor-free space boundary is equal to the surface charge density (rho) on the conductor...