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The animation represents a traveling electromagnetic wave in the z direction. You can click-drag to the right or left to rotate about the z axis. Click-drag up or down to rotate in the xy plane. Restart. Which wave is the electric field and which one is the magnetic field?

Note that both the electric and magnetic fields in this animation are drawn with equal magnitude so you can see both fields. In reality, the magnetic field would be a factor of c smaller than the electric field in MKS units.

Problem authored by Melissa Dancy and Wolfgang Christian.