ANSWER TO CHAPTER 32 HOMEWORK

1.  (a)  If we write the argument of the cosine function as kz + wt = k(z + ct), we see that the wave is traveling in the -z direction.

          Because E and B are perpendicular to each other and to the direction of propagation, and E is in the x-direction, B can have only y-component, with magnitude  B_o = E_o/c.

          Because a rotation of E into B must give the direction of propagation, -z-direction, B must be in the  -y-direction.

     (b) the wave is traveling in the -z-direction.

2.  The energy per unit area per unit time is

                     S = ce_oE_rms²

                        = (3.00 x 10⁸m/s)(8.85 x 10^-12C²/N.m²)(28.6 x 10^-3V/m)² = 2.17 x 10^-6W/m².

       We find the energy transported from

                      U/t = AS = (1.00 x 10^-4m²)(2.17 x 10^-6W/m²)(3600s/h) = 7.82 x 10^-7J/h.