<Dd> H = v × D (\ displaystyle \ mathbf (H) = \ mathbf (v) \ times \ mathbf (D)) or </Dd> <Dd> B = 1 c 2 v × E (\ displaystyle \ mathbf (B) = (\ frac (1) (c ^ (2))) \ mathbf (v) \ times \ mathbf (E)) </Dd> <P> where r ^ ′ (\ displaystyle \ mathbf (\ hat (r))') is the unit vector pointing from the current (non-retarded) position of the particle to the point at which the field is being measured, and θ is the angle between v (\ displaystyle \ mathbf (v)) and r ′ (\ displaystyle \ mathbf (r)'). </P> <P> When v ≪ c, the electric field and magnetic field can be approximated as </P>

State biot savart law and express this law in vector form