Question

If an electromagnetic wave of frequency $5MHz$ travels from vacuum into dielectric medium of electrical permittivity $\epsilon =4$, then its (take ${\mu }_r=1$)

• A. wavelength is halved and the frequency remains unchanged
• B. wavelength and frequency are both doubled
• C. wavelength and frequency both remain unchanged
• D. wavelength is doubled but the frequency remains unchanged
• E. wavelength remains unchanged but the frequency is doubled

Answer 1

Answer: (A)

Refractive index
$n=\sqrt{{\mu }_r{\epsilon }_r}=\frac{{\lambda }_{\text{air }}}{{\lambda }_{\text{medium }}}$
Or ${\lambda }_{\text{med }}=\frac{{\lambda }_{\text{air }}}{\sqrt{{\mu }_r{\epsilon }_r}}=\frac{\lambda }{\sqrt{4}}=\frac{\lambda }{2}$