An electromagnetic wave of frequency 3.0MHz passes from Vacuum into a non-magnetic medium with permittivity ∈=25∈0, where ∈0 is the free space permittivity. The change in wavelength is

when an electro magnetic wave is travelled from one medium to another medium its frequency remains constant but its  velocity and wavelength will be changed. Speed of electromagnetic wave in vacuum is  C=1μ0∈0=fλWhere 'f' is frequency and 'λ' is wavelength of electromagnetic waveSpeed of electromagnetic wave in a medium is C'=1kμ0∈0 where 'K' is dielectric constant C'=1kμ0∈0=fλ'  where λ' is wavelength of wave in a mediumTherefore,  fλ'fλ=1k ⇒λ'=λk ⇒λ'=λ∈∈0 λ'=λ25⇒λ'=λ5Change in wavelength is  λ'−λ=λ5−λ ⇒λ'−λ=−45λ=−45×Cf ⇒λ'−λ=−45×3×1083×106=−4005               ∴λ'−λ=−80m