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Physics · 2026 · 3 marks
CBSE 2026 · Region 3 · Set 1 · Q25
(a) Depict the variation of electric field ( E ) and magnetic field ( B ) with respect to the direction of propagation of an electromagnetic wave.…
(a)
Depict the variation of electric field $\displaystyle (\overrightarrow{\mathrm{E}})$ and magnetic field $\displaystyle (\overrightarrow{\mathrm{B}})$ with respect to the direction of propagation of an electromagnetic wave. Write their two important characteristics.
(b)
Show that $\displaystyle \frac{1}{\sqrt{\varepsilon_{0} \mu_{0}}}$ gives the velocity of an electromagnetic wave in free space.
Marking-scheme solution
(a)
Characteristics of an electromagnetic wave (any two):
(i)
Electric and magnetic fields are perpendicular to each other.
(ii)
Speed of an electromagnetic wave in free space or vacuum is equal to $\displaystyle 3 \times 10^{8} \mathrm{~ms}^{-1}$.
(iii)
Electric and magnetic fields are in the same phase.
(iv)
Electromagnetic waves are transverse in nature.
(v)
Electromagnetic waves can travel in vacuum.
(b)
$\displaystyle \dfrac{1}{\sqrt{\mu_{0} \varepsilon_{0}}}=\dfrac{1}{\sqrt{4 \pi \times 10^{-7} \times \dfrac{1}{4 \pi \times 9 \times 10^{9}}}}$
$\displaystyle =\sqrt{9 \times 10^{16}}$
$\displaystyle =3 \times 10^{8} \mathrm{~m} / \mathrm{s}$ = velocity of an electromagnetic wave in free space.
All Electromagnetic Waves questions2026 question paperNCERT solutions: Electromagnetic WavesPractice Electromagnetic Waves →
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