Question

If an electromagnetic wave of frequency $5 \,MHz$ travels from vacuum into dielectric medium of electrical permittivity $ε = 4$, then its (take $µ_r = 1$)

• 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
$n=\sqrt{\mu_{r} \varepsilon_{r}}=\frac{\lambda_{\text {air }}}{\lambda_{\text {medium }}}$
Or $\lambda_{\text{med }}=\frac{\lambda_{\text {air }}}{\sqrt{\mu_{r} \varepsilon_{r}}}=\frac{\lambda}{\sqrt{4}}=\frac{\lambda}{2}$