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Springs and Electric Field

  1. Mar 16, 2008 #1
    1. The problem statement, all variables and given/known data
    A rigid rod of mass m and length l is suspended from two identical springs of negligible mass such that one spring is attached at either end of the rod. The upper ends of the springs are fixed in place and the springs stretch a distance d under the weight of the suspended rod. I did manage to solve this and find the k=(ma)/(2d) however the question will continue to say If the springs are a part of a circuit connected to a battery with negligible internal resistance and E with a Resister with resistance R and a switch(there is a picture however it is not of much use) Then the rod will move by delta d down from the springs. The total resistance of the circuit is R (the same as the one resister, assuming the wires have negligible resistance.) The rod is in uniform magnetic field directed perpendicular to the field the upper ends of the springs remain fixed in place and the switch is closed. When the system comes to equilibrium the rod is lowered by the prior mentioned delta d.
    a)What is the direction of the magnetic field according to the coordinate axis with x to the right y up and z out of the page
    b)Determine the magnitude of the magnetic field in terms of: m, d,delta d, E (epsilon) R and fundimental constants.
    c) when the switch is suddenly opened the rod oscillates. For these oscillations determine the following in terms of d delta d and fundamental constants, the period (T) and the max speed of the rod.

    Relevant equations

    3. The attempt at a solution
    I got a using the right hand rule however beyond there I am clueless please help. This is a high school AP physics class with no calculus please, thank you much.
  2. jcsd
  3. Mar 17, 2008 #2


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