Recent content by Kyle91

  1. K

    Understanding ray diagrams for concave lenses

    Hey guys, So some friends and I are studying for a test and we came across this question. I've absolutely no idea what the answer is simply because every website I've found only shows parallel rays and a ray going through the centre of the lens. It's incredibly aggravating. Anyway here's the...
  2. K

    Why can we see light when looking down a metallic tube? TEM modes can't exist.

    Yeah I know that Transverse Electric (TE) and TM modes can exist in these type of waveguides but I was under the impression light we see has to have an Electric and Magnetic component. Does that mean that we can see EM waves with no M or no E field? ---- Edit: I should have been more clear, I...
  3. K

    Why can we see light when looking down a metallic tube? TEM modes can't exist.

    So what are you saying is wrong? Those formulas clearly show that EM waves propagating in z cannot exist - assuming perfectly conducting, propagation solely in z etc. etc.
  4. K

    Why can we see light when looking down a metallic tube? TEM modes can't exist.

    I don't think I communicated clearly. Look on that same wikipedia page under Analysis, it says - This is due to - If we sub in Ez and Hz = 0 (being transverse Electromagnetic Waves) then Ex = Hx = Ey = Hy = 0. And so there cannot exist a transverse electromagnetic wave in a perfectly...
  5. K

    Why can we see light when looking down a metallic tube? TEM modes can't exist.

    Hey everyone, I'm going over my course content for an exam this Saturday and I'm a bit confused by a realisation I've just had. In a metallic waveguide we know there are no TEM modes. But wouldn't this mean that we couldn't see through metallic waveguides as we see electromagnetic radiation...
  6. K

    Intro Electromag Question - Wave Equation

    Hey thank you so much for this, it certainly makes a lot more sense with the three-d wave equation!
  7. K

    Intro Electromag Question - Wave Equation

    Homework Statement Homework Equations The Attempt at a Solution b) I could figure it out if kz was changed to kx... Double Derivative of E(r, t) with respect to x is = 0 Double Derivative of E(r, t) with respect to t is = -ω2*E0*cos(kz - wt + ∅0) Multiply the second term by k2/ω2...
  8. K

    Uncertainty Propagation for the Slope of a Line of Best Fit

    I've already got the relationship such that a straight line will apply. I've made a quick mock up of my actual data - see here http://imgur.com/fbwIb. So what I need to do is find the error in that light blue line. Of course the obvious and inaccurate way to do it would just be to alter...
  9. K

    Uncertainty Propagation for the Slope of a Line of Best Fit

    So I thought I just figured it out. I used the above data points but no where in that formula did it ask for the error in my points. I think that formula is solely used to find the error assuming the data is 'almost linear'. For example if my data points were (0, 8.1), (1, 10.1), (2, 12). There...
  10. K

    Uncertainty Propagation for the Slope of a Line of Best Fit

    Hey thanks for the link! I had a read through but I'm still not fully understanding it. Could you please run me through an example? Let's say I've three data points - (0 +-0.1, 8 +-0.5), (1 +-0.2, 10 +-0.4), (2+-0.3, 12+-0.6) With my line of best fit being y = 2x + 8. Edit: Oh so I only need...
  11. K

    Uncertainty Propagation for the Slope of a Line of Best Fit

    Hi guys, So I'm writing up a physics lab and I have a bunch of data points. All of these data points have both x and y error bars. The relationship between x and y is linear and so I've made a line of best fit using Python passing through the data. Now the slope of that line of best fit...
  12. K

    Easy Electrodynamics Question on Field Lines

    Homework Statement Explain why the electric field is perpendicular to any conducting surfaces in static situations. Is this true in general (i.e. even for changing electric or magnetic fields)? Are there similar conditions on the direction of a magnetic field at the surface of a...
  13. K

    Energies of a Quantum Harmonic Oscillator

    Hey guys I was just looking over a past homework problem and found something I'm not too sure on - A particle is in the ground state of a Harmonic potential V (x) = 0.5mω2x2 If you measured the energy, what are the possible results, and with what probabilities? Now I know the answer...
  14. K

    What are some solutions to the Schroedinger Equation?

    Hey all, I'm trying to study for an exam so I apologise if this isn't the right section. Anyway I noticed over the course of the semester the lecturer saying that we should remember some of the basic solutions to the schrodinger equation. I think he's referring to the infinite square well...
  15. K

    Why is the Gravitational Potential Energy formula negative?

    Hey guys So if I lift a book from the ground it gains potential energy. I do work on the book and when I release it the potential energy that I gave the book pulls the book back down to Earth. However I was looking at a potential energy formula for planets which was V = -GMm/r But...
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