Electric field of plane electromagnetic wave propagating through a non-magnetic medium is given by $\mathrm{E}=20 \cos \left(2 \times 10^{10} \mathrm{t}-200 \mathrm{x}\right) \mathrm{V} / \mathrm{m}$. The dielectric constant of the medium is equal to : (Take $\left.\mu_{\mathrm{r}}=1\right)$
Select the correct option:
A
9
B
1
C
$\frac{1}{3}$
D
3
✓ Correct! Well done.
✗ Incorrect. Try again or view the solution.
Solution
Speed of wave $=\frac{2 \times 10^{10}}{200}=10^8 \mathrm{~m} / \mathrm{s}$
Refractive index $=\frac{2 \times 10^8}{10^8}=3$
Now refractive index $=\sqrt{\varepsilon_r \mu_r}$
$$
\begin{aligned}
& 3=\sqrt{\varepsilon_r(1)} \\
& \Rightarrow \varepsilon_r=9
\end{aligned}
$$
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