Question

Out of the following options, choose the pair of space and time-varying electric fields $\left(E\right)$ and magnetic fields $\left(B\right)$ that would generate a plane electromagnetic wave that progresses in $\left(\right.-z\left.\right)$ direction.

• A. $E_{x ,}B_{y}$
• B. $E_{y},B_{x}$
• C. $E_{x ,}B_{y z}$
• D. $E_{y},B_{z x}$

Answer 1

Answer: (B)

The direction of propagation of electromagnetic wave is perpendicular to the plane in which the electric field and the magnetic field are oscillating.

Mathematically, the direction of propagation of electromagnetic wave is given by
$\Rightarrow \overset{ \rightarrow }{E }\times \overset{ \rightarrow }{B}$
The result of the cross product of electric and magnetic field is $-\hat{k}$ as per question.
By vector product rule:
$\hat{j}\times \hat{i}=-\hat{k}$
Therefore, the electric field should be in $y$ axis and the magnetic field should be in $x$ axis.