An electromagnetic wave of frequency ν = 3.0 MHz passes from vacuum into a dielectric medium with permittivity ε = 4.0. Then (a) wave length is halved and frequency remains unchanged (b) wave length is doubled and the frequency becomes half (c) wave length is doubled and the frequency remains unchanged (d) wave length and frequency both remain unchanged.

Answer: (a). Frequency stays the same across the boundary. n = √(εr) = √(4) = 2 ⇒ v = c/2 λ = v/ν ⇒ wavelength becomes half. So the answer is (a) wavelength is halved and frequency remains unchanged.

An electromagnetic wave of frequency ν = 3.0 MHz passes from vacuum… | JEE Main 2004 (AIEEE)

Q27JEE Main 2004 · AIEEEEasy

Speed of EM Waves in a Medium

An electromagnetic wave of frequency $\nu = 3.0\text{ MHz}$ passes from vacuum into a dielectric medium with permittivity $\epsilon = 4.0.$ Then

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Answer: (a)

Frequency stays the same across the boundary.
$n = \sqrt{\varepsilon_r} = \sqrt{4} = 2 \Rightarrow v = c/2$
$\lambda = v/\nu \Rightarrow$ wavelength becomes half.
So the answer is (a) wavelength is halved and frequency remains unchanged.

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Speed of EM Waves in a Medium question from JEE Main 2004 (AIEEE)

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