d'Alembertian and wave equation.
I am studying Coulomb and Lorentz gauge. Lorentz gauge help produce wave equation: [tex]\nabla^2 V-\mu_0\epsilon_0\frac{\partial^2V}{\partial t^2}=-\frac{\rho}{\epsilon_0},\;and\;\nabla^2 \vec...
View ArticleOptics: Can a magnified real image be larger than the lens diameter?
Hi all, This is probably a silly questions, but I want to be sure :). I'm wondering if a real image, created by a convex lens, can appear larger than the lens diameter itself. As an example, I'm...
View ArticleReflection of particles and light: different reflection surface types
Hi, I'm interested in reflection of both particles and light off surfaces. My problem is associated with a model that I'm working on and can be divided in to two parts as far as I see it. The first...
View ArticlePosition-time equation from force-position equation
I've been trying to obtain an equation of position in terms of time given force in terms of position. I've tried and I think I've managed to obtain an equation of velocity in terms of position using...
View Articlewhy can there be no arcing in a perfect vacuum?
i understand why there can be no breakdown, however "arcing" is just the transfer of electrons. a breakdown in air just provides a path for the electrons to take. But if you have two sharp surfaces,...
View ArticleHomeowners Want to Limit EMF Exposure by AC Units
Hi, I work in the construction industry. I have a homeowner that would like to protect herself from electromagentic field (EMF) exposure. (She fears cancer from EMF's.) The airconditioning unit in...
View ArticleAn intuitive meaning to the phase constant k?
k being the one from the harmonic wave ψ(x,t) = Asin(kx - ωt) where k = 2π/λ The way I see it right now, k is just defined this way to get the period of sin(x) to be λ by using sin(kx), so I wondered...
View ArticleQuestion on Dirac Delta function in Griffiths
My question is in Griffiths Introduction to Electrodynamics 3rd edition p48. It said Two expressions involving delta function ( say ##D_1(x)\; and \;D_2(x)##) are considered equal if:...
View ArticleDirection of Friction for Rolling Motion
A ball is attached with a string on the side. When the string is pulled up, static friction accelerates the ball forward while the tension rotates the ball. When a ball is placed on a incline with...
View Articlekinetic inductance
can self-inductance and kinetic inductance be combined in the same model?
View ArticleStationary wave question
Standing waves are set up on the apparatus. Here the distance from P to Q is L=1.20m and the oscillator is set to a frequency 120Hz. A standing wave appears when the mass of the hanging block is 286.1g...
View Articlekinematics
a man moves in an open field such that after moving 10 m on a straight line he makes a sharp turn of 60 degree to his left .the total displacement after 8 such turns is equal to
View ArticleHow can a conductive surface be held at a desired potential?
I was reviewing some things relating to electric fields around conducting surfaces, and the book I was using (Purcell) mentioned that a conducting surface can be held at any arbitrary electric...
View ArticleElectric potential puzzle
This is question 2.30 from the 2nd edition of the Purcell book on Electricity and Magnetism. It's an interesting puzzle, and I've been thinking about it for a while, but I can't make any headway, so...
View ArticleDo electric fields in a conductor go to zero in all instances?
In the absence of external forces, the electric field inside a conductor is supposed to go to zero. This is because if any field were to exist, then the charges in the conductor would experience force...
View ArticleMagnetic field of a solenoid
I'm a bit confused with the equation for a long solenoid. The usual derivation has us consider a rectangular loop enclosing N number of currents over the length L through it. So by Ampere's law one...
View ArticleWork done on the system
I have little confusion about understanding a lecture note for calculation of work done by a expansion of gas. According to text, Work done against a force w= - Fx So work done on the system by...
View ArticleWeight/Resistance aluminum and plastics
At parity of maximum resistance before failure (in the case of aluminum, deformation), weighs less aluminum or plastic? Let me explain better: if i apply a force of 1000N on one end of a rectangular...
View ArticleHelp understanding Faraday cages.....
I have a basic understanding of electrostatics but can't quite get my head around how a Faraday cage works. If you take a hollow metal sphere for example and bring an external source charge towards the...
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