The electric field of a plane electromagnetic wave, travelling in an unknown nonmagnetic medium is given by, E_y =20 sin (3 × 10^6 x-4.5 × 10^14 t )…

The electric field of a plane electromagnetic wave, travelling in an unknown nonmagnetic medium is given by, $$E_{\mathrm{y}}=20 \sin \left(3 \times 10^6 x-4.5 \times 10^{14} \mathrm{t}\right) \mathrm{V} / \mathrm{m} $$ (where $\displaystyle x, \mathrm{t}$ and other values have S.I. units). The dielectric constant of the medium is $\displaystyle \_\_\_\_$ (speed of light in free space is $\displaystyle 3 \times 10^8 \mathrm{~m} / \mathrm{s}$ )