A plane electromagnetic wave of frequency 500 Hz travelling along x-axis in the air has electric field E = 9.9 V/m. The magnetic field associated with the wave will be:
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → \( 3.3\times10^{-8} \) T
In an electromagnetic wave the field magnitudes are related by \( E = cB \), whatever the frequency; the 500 Hz value is not needed.
\( \displaystyle B = \frac{E}{c} = \frac{9.9\,\mathrm{V\,m^{-1}}}{3\times10^{8}\,\mathrm{m\,s^{-1}}} \)
\( \displaystyle B = 3.3\times10^{-8}\,\mathrm{T} \)
Note: NTA picked this question from an NCERT (2026-27) example and changed the figures. Do not ignore NCERT while practising numericals.
NCERT (2026-27):
Nature of Electromagnetic Waves – …
