What would be the limitations on an AC unit that worked like this?
The unit consists of a single, long rectangular chamber. On the inside is a moving wall. On one side of the wall is a vacuum, and the other side is room-temperature air. The moving wall starts much...
View Articlehow does radius of point spread function affect reconstruction errors?
Hi guys, I've been struggling with this concept for a few days now. I have this *good* image that I am blurring (using a gaussian blur), then adding some small percentage of gaussian white noise to it....
View ArticleShouldn't a wire (coil) just store energy and not give it away?
Hello, I was thinking about induced currents in a wire(coil). For example when a current from an external source passes through a wire - the changing magnetic field induces a current opposing the...
View ArticleWhy does the Lagrangian have negative potential energy?
I am watching Susskind's derivation of Newton's F=ma from the Euler-Lagrange equations (53 minutes in) here http://www.youtube.com/watch?v=3apIZCpmdls for which he uses the Lagrangian of kinetic energy...
View ArticleConfusion regarding the concept of acceleration along a component
Suppose we have a wedge with angle θ on which there is a block. We are pushing the wedge with the least force required to keep the block stationary. If the acceleration of wedge is A then the...
View ArticleQuestion about Dirac Delta function
In page 555, Appendix B of Intro to electrodynamics by D Griffiths: [tex]\nabla\cdot \vec F=-\nabla^2U=-\frac{1}{4\pi}\int D\nabla^2\left(\frac{1}{\vec{\vartheta}}\right)d\tau'=\int D(\vec...
View Articlerealistic acceleration (in g's) check?
Folks - doing some research and just needed a reality check on acceleration - let me know if this makes sense: If I drop an object, it should take roughly 5 cm (.102 sec) to reach 1 m/s, correct? I'm...
View ArticleQuestion in Helmholtz Theorem
In page 555, Appendix B of Intro to electrodynamics by D Griffiths: [tex]\nabla\cdot\vec F=D,\;\nabla\times\vec F=\vec C\;\Rightarrow\;\nabla\cdot \vec C=0[/tex] Griffiths let ##\vec F=-\nabla...
View ArticleDifference between Impulse and Momentum
What's the difference between impulse and momentum ? When do we use impulse or when do we say a body has impulse ?
View Articlesolving paraxial equation (to get cavity modes)
Hello, I've been going through some cavity material and attempted analyses regarding transverse modes. Invariably, they always deal with general solutions of paraxial equation and do not have solutions...
View ArticleUnderstanding the physics of antennas
I'm currently preparing for a challenge exam, and I'm having trouble understanding antennas. My physics book is good, but it is very brief in its section on antennas. I know there are more complicated...
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Z0 of a line with unequal wires
In case of a transmission line consisting of two wires in parallel (aka Balanced line) the characteristic impedance Z0 is given by this equation: where l is half the distance between the wire centres,...
View ArticleHow can you guess solutions of parametric resonance equation?
Hi, first time asking questions in this forum. I am self-learning classic mechanics this summer using Laudau's book and so far I feel everything is pretty interesting and makes sense for me. But still,...
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Perpetua mobile theoretical misunderstanding
Hello I was patent examiner on the Portuguese patent office for 3 years and we have a lot of perpetua mobile applications, so I wanted to find now, the theoretical misunderstanding I'm missing here...
View ArticleMagnetic field and respecetive force
Hello I just want you to explain me a bit of physics, cause I am a lay. How to relate (which formula) the magnetic field of a permanent magnet, the vector B at each point (x,y,z), with the force...
View ArticleHow to find the "mass-energy" in a certain field
I saw somewhere that for a charged particle of radius R, the method of finding the "mass-energy" in such an electrostatic field (caused by the charged particle is) M = ∫E^2 dV, where E is the electric...
View ArticleCapacitance needed to heat Nichrome wire 34°
Hi PF! I'm working on a portable heating circuit. I'd like to use an ultracapacitor charged by 2 AA batteries to increase the temperature of 2.25m of 1mm Nichrome wire by 34° in 6 seconds. The question...
View ArticleE&M and relativity
I remember when I took E&M my teacher said that special relativity was built into Maxwells equations. Lets look at a line charge moving at non-relativistic speeds first. We use amperes Law to find...
View ArticleVoltage & Galvanic Cells
In a galvanic cell, electrons are supplied by oxidation at the anode. I am struggling to find clarity on what makes the electrons move from the anode to the cathode when a wire is connected between the...
View ArticlePartial vacuum due to a fan
My understanding is that when a fan begins spinning, a partial vacuum is created. Physically, what creates this partial vacuum? Does the motion of the blades create a void in which there are fewer air...
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