Field Amplitude Relation

For an electromagnetic wave in vacuum the peak electric and magnetic field magnitudes are not independent; they are locked together by the wave speed through E_0 = cB_0. This relation comes straight from Maxwell's equations and ensures that the electric and magnetic energy densities stay equal. Rearranging gives B_0 = E_0/c = 90/(3.0 \times 10^{8}) = 3.0 \times 10^{-7}\ \text{T}. The 3.0 \times 10^{-6}\ \text{T} value is ten times too large, a common decimal slip. The huge 2.7 \times 10^{10}\ \text{T} option comes from mistakenly multiplying by c instead of dividing. The 30 T answer would treat the relation as E_0/3 with the wrong power of ten, which is physically absurd for radiation. The numerical smallness of B_0 reflects the factor of c separating the two fields, exactly as described in the NCERT Electromagnetic Waves chapter. As a sanity check, magnetic field amplitudes in ordinary light are always extremely small, on the order of 10^{-7}\ \text{T} or less, so the chosen answer is physically reasonable.