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Physics Resonance: Problem set 24 -->

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Saturday, 12 November 2016

Problem set 24

  1. The Hamiltonian of a simple pendulum consisting of a mass m attached to a massless string of length l is H = \frac{p_\theta^2}{2ml^2}+ mgl(1- \cos\theta). If L denotes the Lagrangian, the value \frac{dL}{dt} is:
    1. -\frac{2g}{l}p_\theta\sin\theta
    2. -\frac{g}{l}p_\theta\sin{2\theta}
    3. \frac{g}{l}p_\theta\cos{\theta}
    4. lp_\theta^2\cos{\theta}
  2. Two bodies of equal mass m are connected by a massless rigid rod of length l lying in the XY-plane with the centre of the rod at the origin. If this system is rotating about the z-axis with a frequency \omega, its angular momentum is
    1. ml^2\omega/4
    2. ml^2\omega/2
    3. ml^2\omega
    4. 2ml^2\omega
  3. An infinite solenoid with its axis of symmetry along the z-direction carries a steady current I. The vector potential \vec A at a distance R from the axis
    1. is constant inside and varies as R outside the solenoid
    2. varies as R inside and is constant outside the solenoid
    3. varies as \frac{1}{R} inside and as R outside the solenoid
    4. varies as R inside and as \frac{1}{R} outside the solenoid
  4. Consider an infinite conducting sheet in the xy-plane with a time dependent cunent density Kt\hat i, where K is a constant. The vector potential at (x, y,z) is given by \vec A=\frac{\mu_0K}{4c}(ct-z)^2\hat i. The magnetic field \vec B is
    1. \frac{\mu_0Kt}{2}\hat j
    2. -\frac{\mu_0Kz}{2c}\hat j
    3. -\frac{\mu_0K}{2c}(ct-z)\hat i
    4. -\frac{\mu_0K}{2c}(ct-z)\hat j
  5. When a charged particle emits electromagnetic radiation, the electric field \vec E and the Poynting vector \vec S = \frac{1}{\mu_0} \vec E\times\vec B at a large distance r from the emitter vary as \frac{1}{r^n} and \frac{1}{r^m} respectively. Which of the following choices for n and m are correct?
    1. n = 1 and m=1
    2. n = 2 and m=2
    3. n = 1 and m=2
    4. n = 2 and m=4

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