An observer in an inertial frame finds that at a point P the Electric field vanishes but the Magnetic field does not. This implies that in any other inertial frame the electric field E and the magnetic field B satisfy: [these values in vectors] 1. |E|2 = |B|2 2. E . B = 0 3. E x B = 0 4. E = 0 I know the answer is E.B = 0 but why is that?