bottle. sound by blowing across the top
sound created by blowing accross the top of the bottle produces sound due to standing waves created on air inside the bottle. why blowing inside the bottle does not produce sound but only across? how...
View ArticleClik here to view.
lens to lens distance is not 2f in "4f system"
Dear, I studied 4f system and I've got a question. As far as I know, 4f system is optical filtering system (attached file). In the configuration in the attached file, region between L1~L2 is infinity...
View ArticleInteraction between 2 charges moving at the same velocity
How does a moving point charge affect another point charge moving at the same velocity and separated by some distance in one direction relative to an observer whom the charge are moving? What formula...
View Articleds/dt and dr/dt
This is one very basic question. But I just need to confirm if I understood it right. Suppose a particle moves along a curve and crosses Δs path in Δt time. Then we can say the velocity of the particle...
View ArticleWhat Exactly is Light?
I've heard that a changing electric field creates a magnetic field and a changing magnetic field creates an electric field, but I am still very confused about exactly how this propagation actually...
View ArticleMeaning of Dyadic Green Function in Electromagnetism
I know that in the vector potential formulation one can use a scalar Green function (to find the said potential and from then on the electric and magnetic fields), and that this works because the...
View ArticleWhy won't a magnet slow down when falling through a copper coil?
Please watch this video (link: http://www.youtube.com/watch?v=JN-A3RryOC8) for reference. As you can see, the magnet does not slow down (at least, not appreciably) when falling through the copper...
View ArticleOscillation of a liquid in U -tube
I am facing difficulty in understanding a key point . Hence I am putting it here instead of Introductory Physics section . Here is a part of the solution provided by the teacher ,but it doesn't look...
View ArticleSpring scale w/ Different Forces
I have two questions that I think are analogous (tell me if they are not). 1. If I have a spring scale and apply 50 pounds of force to one side and 40 pounds to the other, what would it read and why?...
View Articlemechanistic analysis of lambertian and isotropic radiators
Hello Physics Forums I need a little help wrapping my head around the concept of lambertian emitters as compared to isotropic emitters. As I understand it a lambertian emitter emits less and less...
View ArticleProblem understanding the derivation of the Boltzman distribution
I am currently reading "Quantum Physics of Atoms, Molecules, Solids, Nuclei, and Particles" by Robert Eisberg and Robert Resnick (2nd edition). In Appendix C they derive the boltzman distribution and...
View ArticleVariation of a quantity
Suppose I have such an equation: [itex]A= f(B)[/itex] so [itex]A[/itex] is a function of [itex]B[/itex]. Can I really use the fact that a variation of [itex]A[/itex] is like taking the differential of...
View ArticleFree energy flow
Hello, I am working on non linear fluid dynamics with my professor. We are trying to model multiphase flows of immiscible fluids. And my professor today asked me to look up works on 'free energy...
View ArticleBuoyant force on a submerged cube
So a cube submerged in water will experience pressure on all six sides, and the pressure on the bottom will be greater than the pressure at the top (assuming there's gravity) and the cube will float to...
View ArticleIntensity and frequence of light
I have a doubt that can we increase the intensity of light without changing its amplitude and by increasing its frequency ? :what:
View ArticleDoes a rotating point charge constitute a current ?
Does a point charge 'q' (say an electron) moving with constant angular speed ω in a circle of radius R constitute a current ? A rotating ring of uniform charge density is treated as a current flowing...
View ArticleShield low-frequency magnetic fields, but not high-frequency ones
I am wondering if it is possible to shield strong (1 Tesla) DC magnetic fields with high attenuation factor (10^4 or better) WITHOUT also shielding AC magnetic fields above frequencies of ~10kHz. I...
View ArticleLagrangian density, regular Lagrangian, E&M
Greetings, I have two semi-related questions. 1. When making the Lagrangian formalism of electrodynamics, why is it that we use the Lagrangian density [itex]\mathcal{L}[/itex], rather than the plain...
View ArticleProof of Fermat and HuygensFresnel principle
Hey guys, I don't know if here is the right section for this question but anyway. So I was looking for the proof or derivation of the Fermat's principle and all I got was the HuygensFresnel principle....
View ArticleVector Calculus Question in Lagrangian Mechanics
Hi guys. I hope this isn't a bad place to post my question, which is: I'm reading some lecture notes on Lagrangian mechanics, and we've just derived the Euler-Lagrange equations of motion for a...
View Article