Electromagnetic Waves - Result Question 8
8. 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 :
(a) $2 m^{-1}$
(c) $6 m^{-1}$
(b) $0.5 m^{-1}$
(d) $3 m^{-1}$
[2012]
Show Answer
Answer:
Correct Answer: 8. (a)
Solution:
- (a) On comparing the given equation to
$\vec{E}=a_0 \hat{i} \cos (\omega t-k z)$
$\omega=6 \times 10^{8}$
Wave factor,
$k=\frac{2 p}{r}=\frac{w}{c}$
$k=\frac{\omega}{c}=\frac{6 \times 10^{8}}{3 \times 10^{8}}=2 m^{-1}$
