Electromagnetic Waves Ques 33
33. The electric field associated with an e.m. wave in vacuum is given by $\vec{E}=\hat{i}$ $ 40 \cos (k z-6 \times$ $10^{8} t$ ), where $E, z$ and $t$ are in volt $/ m$, meter and seconds respectively. The value of wave vector $k$ is :
[2012]
(a) $2 $ $m^{-1}$
(b) $0.5 $ $m^{-1}$
(c) $6 $ $m^{-1}$
(d) $3 $ $m^{-1}$
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Answer:
Correct Answer: 33.(a)
Solution:
- (a) On comparing the given equation with
$\vec{E}=a_0 \hat{i} \cos (\omega t-k z)$
$\omega=6 \times 10^{8}$
Wave factor,
$k=\frac{2 p}{r}=\frac{w}{c}$
$k=\frac{\omega}{c}=\frac{6 \times 10^{8}}{3 \times 10^{8}}=2 $ $rad/m$
BETA
