8/05  Because we were short of time, I did not give you
      today's ungraded HW during lecture.  Here it is:
      Consider a series AC circuit with a generator, a
      resistor, and a capacitor, and with inductance which
      is small enough to ignore. R = 45 kOhms, C = 355 pF,
      and the driving angular frequency is 100,000 rad/s.
      The capacitor voltage has been measured to be 
      (0.262 V) times a sine function of omega_driving
      times the time.  Show that the maximum resistor
      voltage must be 0.419 V, and that the maximum
      generator EMF must be 0.494 V.

7/23  Because we were short of time, I did not give you
      today's ungraded HW during lecture.  Here it is:
      Show how to use the Biot-Savart Law to show that
      (a) For a current segment of length L oriented on
      the y axis from the origin to the point (0,L), with
      the current in the +y direction, the magnetic field
      strength created at a point P at location x on the
      x axis is
                  B = (k/c^2)*(IL/(x*sqrt(L^2+x^2))).

      (b) For a quarter circle (radius R) of current I
      flowing clockwise from the point (-R,0) to the
      point (0,R), the magnetic field strength created
      at the origin is
                          B = mu_0*I/(8*R).

      Thanks. GBA

7/17  Because we were short of time, I did not give you
      today's ungraded HW during lecture.  Here it is:
      A metal rod sticking vertically into the ground
      has just been struck by lightning.  As a result,
      a momentary current of size I is flowing from the
      bottom of the rod into the ground; assume that this
      current is spreading uniformly into a hemisphere of
      ground centered at the bottom end of the metal rod.
      At this location, the resistivity of the ground has
      a value rho.  Show that, while the current I is
      flowing, there must be an electric field of magnitude

              E(r) = rho*I/(2*pi*r^2)

      existing within the ground near the bottom end of
      the metal pole, where r represents the distance
      from the bottom end of the pole.  Thanks.  GBA

7/15  I neglected to give you the ungraded HW for today.
      Here it is.  Use Gauss' Law and the definition of
      capacitance to show that nested, concentric, spherical
      metal shells of radius a and b (b>a) have a capacitance
      of (k*((1/a)-(1/b)))^(-1).

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