# Search results

1. ### Why does perspective skew some lines and not others?

Imagine looking at a set of x-y-z axes, from directly along the z-axis. Say in this image, the road is the line z=0. Why is it, that only lines on or parallel to the z-axis get skewed? All the surfaces that are in or parallel to the x-y plane remain undistorted, and their angles are at 90...
2. ### LaTeX PS and Jpg in Latex Files

Hi everyone, I was wondering if someone could clarify how to put both .ps and .jpg files in the same latex file. At the minute I'm having to convert all my .jpgs to .ps using photoshop then compiling my latex file by going Latex->PS->PDF. However all my converted jpgs look all pixelated...
3. ### Net Flux from isotropic source

Hi everybody. Apologies for asking what may be a very simple question, but in every text book I've read, they say that the net flux through an area dA from an isotropic emitter is zero. But it also says that the sun is an isotropic emitter. Now hold on, the net flux from the sun is clearly...
4. ### Electron Transitions: Superposition of States

It'd be great if you could help me clarify a few things in my head. Firstly I've got written in my notes "quantum mechanics forbids spontaneous transitions from one energy level to another because energy eigenfunctions are time independent". However this seems a bit of a circular...
5. ### Twin paradox without length contraction

Hi all, apologies if this has been posted a million times before.... I'm trying to explain the twin paradox without getting involved with length contraction. One way to think of it is Twin A remains at rest on Earth then twin B goes off at 4c/5 to Alpha centauri 4 light years away, then...
6. ### Speed of light pulse if you have a velocity of c

Homework Statement A light pulse is emitted in an inertial frame. You are moving at a constant velocity of c AWAY from the pulse, and initially 10m away from the pulse. Will the pulse reach you, and what velocity will you measure for c? Homework Equations The Attempt at a...
7. ### Perturbation in Infinite Square well

Homework Statement Calculate the 1st order probability an electron in the ground state of an infinite sqaure well (width 1) will be found in the first excited state t seconds after the pertubation H=sin(PI*x) is switched on. Homework Equations Transition frequency is omega_12 The Attempt...
8. ### Michelson Interferometer Pattern

Homework Statement Explain how a pattern of straight line fringes of equal thickness can be observed in a michelson interferometer. Homework Equations see diagram 1/3 of the way down page at http://www.holo.com/holo//book/book6&7.html [Broken] The Attempt at a Solution I really...
9. ### Microscopic Ohm's Law

Homework Statement Explain the terms used in the microscopic version of Ohm's Law Homework Equations j=oE The Attempt at a Solution Well I know what we have here is the current density within a conductor is equal to its conductivity multiplied by an 'E-field'. But what is this...
10. ### Work: Sign Convention Problem

Homework Statement One mole of an ideal gas at 300K expands isothermally from a pressure of 2x10^6 Nm^-2 to a pressure of 2x10^5 Nm^-2. Calculate the work done ON the gas. Homework Equations dW = PdV The Attempt at a Solution Following through the integral, it becomes clear that work...
11. ### Magnetic Field Vector due to Infinitely long wire

Hi everybody, I have quite a simple question here. I know that for an infinitely long current carrying wire, the magnitude of the magnetic field is given by (mu_0*I)/(2*Pi*R) where mu_0 is the magnetic permeability of free space. What I would like to know is what is the vector form of...
12. ### Electric Field due to a charged conducting finite cylindrical shell.

Hi everyone. I'm having a bit of trouble with finding an electric field. Basically, I'm trying to understand the formula for a cylindrical capacitor, so the method involves integrating the field between two conducting cylindrical shells. Firstly can Gauss's law be used in this case, because the...