JEE MainPhysicsElectromagnetic Waves
Which of the following combinations of directions for the electric field ( E ), magnetic field ( B ), and wave propagation ( S ) is NOT physically possible for an electromagnetic wave in a vacuum?
Options
- AE along -z , B along +y , S along -x
- BE along +y , B along +z , S along +x
- CE along -x , B along -z , S along -y
- DE along +z , B along +x , S along +y
Correct answer
A. E along -z , B along +y , S along -x
Step-by-step solution
The direction of wave propagation S must be along the direction of E B . Let us check each option: For the first option: E is along - k and B is along + j . E B = (- k ) ( j ) = -( k j ) = -(- i ) = + i (positive x -direction). However, the given propagation direction is -x . Thus, this combination violates the cross-product rule and is not possible. For the second option: E is along + j and B is along + k . E B = ( j ) ( k ) = + i (positive x -direction). This is possible. For the third option: E is along - i and