JEE MAIN - Physics (2023 - 25th January Morning Shift - No. 13)
An 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?
Negative direction of $$y$$
Positive direction of $$z$$
Positive direction of $$x$$
Negative direction $$x$$
Explanation
As, poynting vector
$$ \overrightarrow{\mathrm{S}}=\overrightarrow{\mathrm{E}} \times \overrightarrow{\mathrm{H}} $$
Given energy transport $=$ negative $\mathrm{z}$ direction
Electric field $=$ positive $\mathrm{y}$ direction
$(-\hat{\mathrm{k}})=(+\hat{\mathrm{j}}) \times[\hat{\mathrm{i}}]$
Hence according to vector cross product magnetic field should be positive $\mathrm{x}$ direction.
$$ \overrightarrow{\mathrm{S}}=\overrightarrow{\mathrm{E}} \times \overrightarrow{\mathrm{H}} $$
Given energy transport $=$ negative $\mathrm{z}$ direction
Electric field $=$ positive $\mathrm{y}$ direction
$(-\hat{\mathrm{k}})=(+\hat{\mathrm{j}}) \times[\hat{\mathrm{i}}]$
Hence according to vector cross product magnetic field should be positive $\mathrm{x}$ direction.
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