JEE Main · 2021 · 18 Mar 2021 · Shift 2 · EM Waves

A plane electromagnetic wave propagating along y-direction, can have the following pair of electric field (

E

) and magnetic field (

B

) components :

Answer: (D)

Solution

In a plane electromagnetic wave

E

B

and the direction of travel form a right-handed orthogonal set, with

E \times B

along the direction of propagation. A wave moving along

y

can therefore have no field component along

y

, and the two fields must be perpendicular to each other within the

x

z

plane. That leaves

E_{z}

with

B_{x}

, since

\hat{k} \times \hat{i} = \hat{j}

, and

E_{x}

with

B_{z}

, since

\hat{i} \times \hat{k} = - \hat{j}

and the wave then runs along the

y

-axis the other way. Pairings such as

E_{y}

with

B_{x}

, or

E_{y}

with

B_{y}

, are ruled out because a

y

component lies along the direction of propagation. The permitted pairs are

E_{x}

with

B_{z}

, or

E_{z}

with

B_{x}

JEE Main · 2021 · 18 Mar 2021 · Shift 2 · Single correct option