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 )…
JEE Main 2026 — Physics Electromagnetism
2026integermedium
The electric field of a plane electromagnetic wave, travelling in an unknown nonmagnetic medium is given by, Ey=20sin(3×106x−4.5×1014t)V/m (where x,t and other values have S.I. units). The dielectric constant of the medium is ____ (speed of light in free space is 3×108m/s)
Official previous-year question
Held on 22 Jan 2026 · Verified 6 Jul 2026.
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Solution
From the wave equation Ey=20sin(3×106x−4.5×1014t):
Wave number: k=3×106 m⁻¹
Angular frequency: ω=4.5×1014 rad/s
Speed of wave in medium: v=kω=3×1064.5×1014=1.5×108 m/s
Speed of light in vacuum: c=3×108 m/s
Refractive index: n=vc=1.5×1083×108=2
For a nonmagnetic medium: n=ϵr
Dielectric constant: ϵr=n2=4
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