At a certain point and a certain time the electric field of an electromagnetic wave is in the negative z direction and the magnetic field is in the positive y direction.Which of the following statements is true?
A)Energy is being transported in the positive x direction but half a cycle later, when the electric field is in the opposite direction, it will be transported in the negative x direction.
B)Energy is being transported in the positive x direction and half a cycle later, when the electric field is in the opposite direction, it will still be transported in the positive x direction.
C)Energy is being transported in the negative x direction but half a cycle later, when the electric field is in the opposite direction, it will be transported in the positive x direction.
D)Energy is being transported in the negative x direction and half a cycle later, when the electric field is in the opposite direction, it will still be transported in the negative x direction.
E)None of the above is true.

Question

Quizplus · Accepted Answer

The direction of energy transport in an electromagnetic wave is given by the Poynting vector, which is the cross product of the electric field vector and the magnetic field vector. Given the electric field is in the negative z direction and the magnetic field is in the positive y direction, their cross product points in the positive x direction, indicating the direction of energy transport. This direction does not change with the oscillations of the wave; thus, even half a cycle later when the electric field is in the opposite direction, the energy will still be transported in the positive x direction.

At a Certain Point and a Certain Time the Electric