JEE Main · 2004 · 24 Apr 2004 · Offline · EM Waves

An electromagnetic wave of frequency

v = 3.0

MHz passes from vacuum into a dielectric medium with permittivity

ε = 4.0

. Then

(A)wavelength is doubled and the frequency remains unchanged
(B)wavelength is doubled and frequency becomes half
(C)wavelength is halved and frequency remains unchanged✓ Correct
(D)wavelength and frequency both remain unchanged.

Answer: (C)

Solution

The medium has refractive index

μ = \frac{ε}{ε _{0}} = 4 = 2

, so light slows to

\frac{c}{2}

on entering it. The frequency is set by the source and does not change, so from

v = f λ

the wavelength must fall by the same factor of two. The wavelength is halved while the frequency stays unchanged.

JEE Main · 2004 · 24 Apr 2004 · Offline · Single correct option

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