The amplitude of the magnetic field of a harmonic electromagnetic wave in vacuum is \( B_{0} = 450 \) nT. What is the amplitude of the electric field of the wave?
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \( 135\,\mathrm{N\,C^{-1}} \)
In an electromagnetic wave the amplitudes of the electric and magnetic fields are related through the speed of light: \( E_{0} = cB_{0} \), where \( c = 3\times10^{8}\,\mathrm{m\,s^{-1}} \) in vacuum.
\( B_{0} = 450\,\mathrm{nT} = 450\times10^{-9}\,\mathrm{T} = 4.5\times10^{-7}\,\mathrm{T} \)
\( E_{0} = cB_{0} = (3\times10^{8})(4.5\times10^{-7}) = 135\,\mathrm{N\,C^{-1}} \)
Note: NTA picked this question from an NCERT (2026-27) exercise and changed the figures. Do not ignore NCERT while practising numericals.
NCERT (2026-27):
Exercises – …
