Adipole antenna is located at the origin with its axis along the z-axis. as the antenna's electric current oscillates up and down the z-axis, polarized electromagnetic radiation travels away from the antenna along the positive y-axis. what is a possible direction of the radiation's oscillating magnetic field at point y=10m on the y-axis?
x-direction
y-direction
z-direction
45° between the positive x- and positive y-directions
45° between the positive x- and positive z-directions

The direction of an EM wave's Poynting vector determines the direction of the wave's propagation:

S = 1/μ₀(E×B)

S is the Poynting vector, μ₀ is the magnetic constant, E is the electric field vector, and B is the magnetic field vector. Note that we are taking the cross product between E and B, not taking the product of two scalar quantities.

Since S depends on the cross product of E and B, you may use the right hand rule in the following way to determine the direction of B:

You can conclude that B must point along the x axis.

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