CBSE Class 12 · 2008 · All India · EM WavesShort Answer

An electromagnetic wave is travelling in a medium with a velocity

v = v \hat{i}

. The electric field oscillations of this wave are along the y-axis.
(a) Identify the direction along which the magnetic field oscillations take place.
(b) How are the magnitudes of the electric and magnetic fields in the wave related to each other?

Answer: (a) Along the z-axis.
(b) $E_{0} = c B_{0}$ , i.e. $E / B = c$ .

Solution

(a) For an electromagnetic wave,

E

B

and the direction of propagation form a right-handed set, with

E \times B

along

v

.
With

v

along

\hat{i}

(x) and

E

along

\hat{j}

(y), the magnetic field must oscillate along

\hat{k}

(z).
(b) The field magnitudes are related by

E_{0} = c B_{0} \Rightarrow \frac{E}{B} = c

B ∥ \hat{k}, E_{0} = c B_{0}

CBSE Class 12 Board · 2008 · All India · Subjective

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