Question

If the direction of electric and magnetic field vectors of a plane electromagnetic wave are along positive $y$ direction and positive $z$ direction respectively, then the direction of propagation of the wave is along

• A. positive $z$ direction
• B. negative $z$ direction
• C. negative $y$ direction
• D. positive $x$ direction
• E. negative $x$ direction

Hint:

Use right-hand rule: $\vec{E} \times \vec{B}$ gives wave direction.

Answer 1

The Correct Option is D

Concept: Direction of EM wave propagation
The direction of propagation is given by the Poynting vector: \[ \vec{S} = \vec{E} \times \vec{B} \] ---

Step 1: Given directions \[ \vec{E} \parallel +\hat{y}, \quad \vec{B} \parallel +\hat{z} \] ---

Step 2: Cross product \[ \hat{y} \times \hat{z} = \hat{x} \] ---

Step 3: Physical meaning
• Electric field oscillates along $y$
• Magnetic field along $z$
• Energy propagates perpendicular to both → along $x$ --- Final Answer: \[ \boxed{\text{positive } x \text{ direction}} \]