Electromagnetic Waves

JEE Main level, single correct, medium

54 of 165

Question 54 of 165

All electromagnetic wave is transporting energy in the negative zz direction. At a certain point and certain time the direction of electric field of the wave is along positive yy direction. What will be the direction of the magnetic field of the wave at that point and instant?

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Answer: (A) Positive direction of xx

In an electromagnetic wave, the direction of energy flow is along the direction of the wave propagation. Therefore, the wave propagates along negative z direction.
Electric field is along the positive y direction and the wave propagates along negative z direction. Thus, magnetic field is in direction perpendicular to both z and y axes.
Using vector algebra,
(−k^)=(+j^)×(i^)(-\hat{k})=(+\hat{j})\times \left(\hat{i}\right)
Hence, magnetic field is in positive xx direction.

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