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# If an electromagnetic wave of frequency $v = 3.0\: MHz$ passes from vacuum into a dielectric medium with permittivity $e = 4.0$ then

$\begin {array} {1 1} (a)\;\text{wavelength is doubled and frequency remains unchanged}\\ (b)\;\text{wavelength is doubled and frequency becomes half} \\ (c)\;\text{wavelength is halved and frequency remains unchanged}\\ (d)\;\text{wavelength and frequency both remain unchanged} \end {array}$

Both speed and wavelength of wave will become half,  the frequency remaining unchanged
(Frequency of a wave depends on the source as due to refraction,
it is assumed that the energy is conserved, so $h\nu$ remains the same.)
Ans : (c)

edited Oct 8, 2014