The electromagnetic wave of the radiation field from a wire antenna travels toward the plane of your paper (which is in the -z direction). At time t = 0 s, the wave strikes your paper at normal incidence. The magnetic field vector at point O in the figure points in the -y direction and has a magnitude of 4.0 × 10 - 8 T. The frequency of the wave is 1.0 × 10 16 Hz.
-What is the direction of electromagnetic energy transport?
A)the positive x direction
B)the negative x direction
C)the positive y direction
D)the negative y direction
E)the negative z direction

Question

The electromagnetic wave of the radiation field from a wire antenna travels toward the plane of your paper (which is in the -z direction). At time t = 0 s, the wave strikes your paper at normal incidence. The magnetic field vector at point O in the figure points in the -y direction and has a magnitude of 4.0 × 10 - 8 T. The frequency of the wave is 1.0 × 10 16 Hz. 
-What is the direction of electromagnetic energy transport?
A)the positive x direction 
B)the negative x direction 
C)the positive y direction 
D)the negative y direction 
E)the negative z direction

Quizplus · Accepted Answer

The direction of electromagnetic energy transport is always perpendicular to the electric and magnetic fields, which in this case are both in the -y direction at point O. Therefore, the direction of energy transport must be perpendicular to the -y direction, which is in the -z direction. Therefore, the answer is E, the negative z direction.

The Electromagnetic Wave of the Radiation Field from a Wire