In a plane electromagnetic wave, the electric field oscillates sinusoidally at a frequency of \( 3 \times 10^{10}\,\mathrm{Hz} \) and its amplitude is 30 V/m. The amplitude of the oscillating magnetic field is:
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → \( 1 \times 10^{-7}\,\mathrm{T} \)
In an electromagnetic wave the ratio of the field amplitudes is the speed of light, \( E_0 = c\,B_0 \). The frequency does not enter this relation.
\( \displaystyle B_0 = \frac{E_0}{c} = \frac{30\,\mathrm{V\,m^{-1}}}{3\times10^{8}\,\mathrm{m\,s^{-1}}} = 1\times10^{-7}\,\mathrm{T} \)
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 – …
