The amplitude of the magnetic field of an electromagnetic wave in vacuum is \( B_0 = 300\,\mathrm{nT} \). What is the amplitude of the electric field part of the wave? (Given speed of light in vacuum, \( C = 3 \times 10^{8}\,\mathrm{ms^{-1}} \))
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → 90 N/C
In an electromagnetic wave in vacuum the amplitudes of the electric and magnetic fields are related by the speed of light.
\( \displaystyle E_0 = c\,B_0 \)
\( B_0 = 300\,\mathrm{nT} = 300\times10^{-9}\,\mathrm{T} = 3\times10^{-7}\,\mathrm{T} \)
\( \displaystyle E_0 = 3\times10^{8}\,\mathrm{m\,s^{-1}} \times 3\times10^{-7}\,\mathrm{T} = 90\,\mathrm{N/C} \)
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 – …
