Chapter 23
----------

1).  The Capacitive Reactance is given by (see formula 23.2)
             X_C = 1/(2*pi*f*C)
     where f is the frequency and C is the capacitance.
     ---> f = 1/(2*pi*X_C*C) = 1/(2*3.14*168 Ohm * 7.5*10^(-6) F) = 126 Hz

4).  The capacitive reactance X_C is: 
             X_C = 1/(2*pi*f*C)
      The capacitance is:
        ---> C =  1/(2*pi*f*X_C) = 1/(2*3.14*170 Hz * 36 Ohm) = 2.6 10^(-5) F
      Using now the capacitance we can get capacitive reactance at a new
      frequency:
           X_C = 1/(2*pi*f*C = 1/(2*3.14*510 Hz * 2.6 10^(-5) F) = 12 Ohm
      Another, quicker way to arrive at the solution is to notice that the
      capacitive reactance is inversely proportional to the  frequency.
      Thus
       X_C1/X_C2 = f2/f1 ==>
          X_C2 = X_C1*f1/f2 = 36 Ohm*(170 Hz/510 Hz) = 12 Ohm

10). The Ohm's law for the inductor is
             V = I * X_L ,
     where I is the current through the inductor, X_L is the inductive 
     reactance. Since X_L = 2*pi*f*L 
      --->   V = I*2*pi*f*L = 2*3.14*750 Hz*0.08 H*0.2 A = 75.3 V

18).  Each component of the system has a resistance or reactance. The
      voltage across each component depends on the current flowing in the
      circuit. The value of the current depend on the total impedance.
      First of all let's find the total impedance of the system:
         Z = sqrt(R^2+(X_L-X_C)^2)
      where X_L is a reactance of the inductor, and X_C is the reactance
      of the capacitor. 
         X_L = 2*pi*f*L = 2 * 3.14 * 1350 Hz * 5.3*10^(-3) H = 44.9 Ohm
         X_C = 1/(2*pi*f*C) = 1/(2*3.14*1350Hz*4.1*10^(-6)F) = 28.8 Ohm
         Z   = sqrt((16 Ohm)^2 + (44.9 Ohm - 28.8 Ohm)^2)    = 22.7 Ohm

      The current in the circuit is equal to
       I = V/Z = 15 V / 22.7 Ohm = 0.66 A

      Potential across the resistor is V=I*R   = 0.66 A * 16 Ohm   = 10.6 V
       --//--             capacitor is V=I*X_C = 0.66 A * 28.8 Ohm = 19 V
       --//--             inductor  is V=I*X_L = 0.66 A * 44.9 Ohm = 29.6 V
     
      Note that the generator voltage 15 V is NOT equal to the sum
      of the voltages across the elements in the circuit, though they
      are connected in series.