In a plane electromagnetic wave, the phase difference between electric and magnetic field vectors is
Answer & explanation
Correct answer: option 1
The correct answer is Option (1) → zero
In a plane electromagnetic wave, E and B are perpendicular in direction but oscillate in phase: they reach their maxima and zeros at the same place and time.
\( E_x = E_0\sin(kz - \omega t) \)
\( B_y = B_0\sin(kz - \omega t) \)
Both have the same phase \( (kz - \omega t) \), with \( E_0 = cB_0 \), so the phase difference is zero.
Why the other options are incorrect
Option (2) \( \pi/4 \) — Incorrect. There is no phase lag of \( \pi/4 \) between the fields; both follow the same sine function.
Option (3) \( \pi/2 \) — Incorrect. \( \pi/2 \) (90°) is the angle between the directions of E and B, not their phase difference.
Option (4) \( \pi \) — Incorrect. A phase difference of \( \pi \) would make B zero or reversed when E is maximum, but E and B peak together.
NCERT (2026-27):
Nature of Electromagnetic Waves – “… The electric and magnetic fields \( E_x \) and \( B_y \) are perpendicular to each other, and to the direction \( z \) of propagation. We can write \( E_x \) and \( B_y \) as follows:
\( \displaystyle E_x = E_0 \sin (kz - \omega t) \qquad [8.7(a)] \)
\( \displaystyle B_y = B_0 \sin (kz - \omega t) \qquad [8.7(b)] \)”