SATHEE: Electromagnetic Waves - Result Question 15

Electromagnetic Waves - Result Question 15

15. If $\vec{E}$ and $\vec{B}$ represent electric and magnetic field vectors of the electromagnetic waves, then the direction of propagation of the waves will be along

[2002]

(a) $\vec{B} \times \vec{E}$

(b) $\vec{E}$

(d) $\vec{E} \times \vec{B}$

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Answer:

Correct Answer: 15. (d)

Solution:

(d) Direction of propagation of electromagnetic waves is perpendicular to Electric field and Magnetic field. Hence, direction is given by

vector $\vec{S} = \vec{E} \times \vec{H} = \frac{\vec{E} \times \vec{B}}{μ_{0}}$ .

In electromagnetic waves, the rate of flow of energy crossing a unit area is described by Poynting vector. The magnitude of poynting vector

$\begin{aligned} | \vec{S} | = \frac{1}{μ_{0}} E B \sin 90^{\circ} = \frac{E B}{μ_{0}} \\ = \frac{E^{2}}{μ_{0} c} (∵ B = \frac{E}{c}) \end{aligned}$

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Electromagnetic Waves - Result Question 15

15. If E→ and B→ represent electric and magnetic field vectors of the electromagnetic waves, then the direction of propagation of the waves will be along

Answer:

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15. If $\vec{E}$ and $\vec{B}$ represent electric and magnetic field vectors of the electromagnetic waves, then the direction of propagation of the waves will be along