Electromagnetic Waves Question 3
Question 3 - 25 January - Shift 1
All electromagnetic wave is transporting energy in the negative $z$ direction. At a certain point and certain time the direction of electric field of the wave is along positive y direction. What will be the direction of the magnetic field of the wave at that point and instant?
(1) Positive direction of $x$
(2) Positive direction of $z$
(3) Negative direction of $x$
(4) Negative direction of $y$
Show Answer
Answer: (1)
Solution:
Formula: Poynting vector
As , poynting vector
$\overrightarrow{{}S}=\overrightarrow{{}E} \times \overrightarrow{{}H}$
Given energy transport $=$ negative $z$ direction
Electric field $=$ positive $y$ direction
$(-\hat{k})=(+\hat{j}) \times[\hat{i}]$
Hence according to vector cross product magnetic
field should be positive $x$ direction.
