Physics Question from JEE Main 2026 · 22 January, Shift 1

The electric field of a plane electromagnetic wave, travelling in an unknown non-magnetic medium is given by,

$$E_y = 20 \sin (3 \times 10^6 x - 4.5 \times 10^{14} t) \, V/m$$

(where $x$, $t$ and other values have S.I. units). The dielectric constant of the medium is _____.