Recent content by jmc8197

  1. J

    Lienard-Wiechert potential for 2 discrete Qs

    I've tried a simple derivation of the Lienard-Wiecher potential for 2 discrete charges seperated by dr, but end up with a result which isn't the same as the theoretically correct version: Take two charges q1 @r1, q2 @r2 with r1 > r2, dr = r1 - r2, parallel and both travelling at velocity v...
  2. J

    Magnetism and closed loops

    All magnetic fields are created by moving charges, whether they are moving in straight lines or orbits within an atom, as in your bar magnet. Secondly, a moving charge within a magnetic field experiences a magnetic force, such that moving charges will tend to attract one another if they are...
  3. J

    Centre of Mass Theorem false for a rotating body?

    Let's consider things simply. The forces acting on the centre of mass are gravity, and the reaction of the table to the support. So another torque must come from the fact that it is precessing, or maybe from spinning? or a combination of the two? I never knew that a gyroscope could generate an...
  4. J

    Centre of Mass Theorem false for a rotating body?

    But surely the centre of mass traces out a circle as it precesses, the com being in the centre of the fly wheel?
  5. J

    Centre of Mass Theorem false for a rotating body?

    For a distributed mass, F = M dv/dt where F is the total external force, M the total mass, and v the velocity of the centre of mass. But take the case of a gyroscope, where the force acting on the centre of mass is gravity, assuming it is uniform over the body. The gyroscope doesn't topple...
  6. J

    Shy girl electrical eng

    Electrical Engineering OK I'm an electrical engineer, and although there were 10% of women engineers on my course and most of them did brilliantly, I've never come across a woman engineer. In the UK, the EE society has gone out of it's way to promote the image of women in engineering, and...
  7. J

    Frequency Response of Amplifiers (BJT and FET transistors)

    The joys of Low, mid and high freq response Well, at "low frequencies" the response is dominated by the high vaue capacitors because the low value capacitors have an impedance that remains high compared to other impedances over the "low frequency response" range. At the mid frequency response...
  8. J

    Some questions on rigid modies in Landau's Mechanics book

    The following comes from Landau's Mechanics, pages 97 - 98. For a particle in a rigid body, v = V + W x r -- (1) where for some origin O of the moving body measured in the "fixed" system of co-ordinates, v = particle's velocity in the "fixed" system, V = velocity of O in "fixed" system...
  9. J

    Question concerning rigid bodies

    The following comes from Landau's Mechanics, pages 97 - 98. For a particle in a rigid body, v = V + W x r -- (1) where for some origin O of the moving body measured in the "fixed" system of co-ordinates, v = particle's velocity in body in the "fixed" system, V = velocity of O in "fixed"...
Top