Field Amplitude Relation

NCERT Class 12, Chapter 8 (Electromagnetic Waves) establishes that in a plane electromagnetic wave the magnitudes of the electric and magnetic fields at every instant are linked by E = cB, where c is the speed of light. This follows directly from Maxwell's equations and reflects the fact that the two fields carry energy together and oscillate in phase, reaching their peaks simultaneously. The same proportionality holds for the peak values, so the peak magnetic field is simply the peak electric field scaled down by the large factor c. To find the peak magnetic field, rearrange to B₀ = E₀/c = 60 / (3 × 10⁸) = 2.0 × 10⁻⁷ T. The value 1.8 × 10¹⁰ T is grossly wrong because it multiplies E by c instead of dividing, giving an absurdly large field. The value 5.0 × 10⁻⁸ T uses an incorrect factor and does not follow from E/c. The value 3.0 × 10⁻⁶ T results from a power-of-ten slip in dividing by the speed of light. A magnitude check confirms that magnetic fields in ordinary electromagnetic waves are extremely small, of the order 10⁻⁷ T for such an electric field, so the chosen value is physically reasonable; this smallness is precisely why the magnetic force on charges in a wave is usually negligible compared with the electric force.