# If an electromagnetic wave of frequency $v = 3.0\: MHz$ passes from vacuum into a dielectric medium with permittivity $e = 4.0$ then
$\begin {array} {1 1} (a)\;\text{wavelength is doubled and frequency remains unchanged}\\ (b)\;\text{wavelength is doubled and frequency becomes half} \\ (c)\;\text{wavelength is halved and frequency remains unchanged}\\ (d)\;\text{wavelength and frequency both remain unchanged} \end {array}$