Electric field of plane | GEOMETRICAL OPTICS

JEE MAIN 2021

01-09-21 S2

Question

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:

$\frac{1}{3}$

✓ 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 $=\sqrt{\varepsilon_r \mu_r}$ $$ \begin{aligned} & 3=\sqrt{\varepsilon_r(1)} \\ & \Rightarrow \varepsilon_r=9 \end{aligned} $$

Question Tags

JEE Main

Physics

Easy

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