What Direction Does the Magnetic Field Oscillate in a Vertically Traveling Wave?

[lisamay44]

If an electric field wave oscillates north and south, and the wave is traveling straight up, then what direction does the magnetic field wave oscillate?

east and west
north and south
up and down
It does not oscillate; this situation is impossible.

I know that magnetic fields and electric fields travel perpendicular to each other. Do they travel perpendicular to each other on two dimensions (then the answer would be east and west) or do they travel perpendicular to each other on three dimensions (and then the answer would be up and down)? My initial reaction is that they travel perpendicular to each other on 3 dimensions (answer = up and down), but I am not sure.

 

[alphysicist]

Hi lisamay44,

You said that the electric and magnetic fields are pependicular to each other in an electromagnetic wave; now how are those fields related to the direction of travel of the wave?

 

[Moetasim]

Your initial reaction is correct. Magnetic and electric fields are perpendicular to each other in three dimensions. Therefore, if the electric field wave is oscillating north and south, the magnetic field wave would be oscillating east and west, as they are perpendicular to each other in three dimensions. This is known as the right-hand rule, where the direction of the electric field is determined by the direction of the thumb and the direction of the magnetic field is determined by the direction of the fingers when the hand is held in a certain position. So, in this case, the fingers would point east and west, perpendicular to the thumb pointing north and south.