The magnetic field of a plane electromagnetic wave is given by \( B_x = 2\times10^{-7}\sin(0.6\times10^{3}y + 2\times10^{11}t)\,\mathrm{T} \). An expression for its electric field is :
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → \( E_z = 60\sin(0.6\times10^{3}y + 2\times10^{11}t)\,\mathrm{V/M} \)
An electromagnetic wave is transverse: the electric field and the magnetic field are perpendicular to each other and to the direction of propagation.
The phase contains \( y \) and \( t \), so the wave travels along the \( y \)-axis. The magnetic field is along \( x \), so the electric field must be along the remaining axis, \( z \).
The amplitudes are related by \( E_0 = c\,B_0 \):
\( \displaystyle E_0 = c\,B_0 = 3\times10^{8}\,\mathrm{m\,s^{-1}} \times 2\times10^{-7}\,\mathrm{T} = 60\,\mathrm{V\,m^{-1}} \)
The electric field oscillates in phase with the magnetic field, so \( E_z = 60\sin(0.6\times10^{3}y + 2\times10^{11}t)\,\mathrm{V/m} \).
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 – …
