Q. An electromagnetic wave of frequency $v = 3.0\ MHz$ passes from vacuum into a dielectric medium with relative permitivity $\varepsilon_{r} = 4.0$. Then
A) Wavelength is doubled and the frequency remains unchanged
B) Wavelength is doubled and frequency becomes half
C) Wavelength is halved and frequency remains unchanged
D) Wavelength and frequency both remain unchanged
Explanation
(c) Refractive index $= \sqrt{\frac{\mu\varepsilon}{\mu_{0}\varepsilon_{0}}}$
Here $\mu$ is not specified so we can consider $\mu = \mu_{0}$
Then refractive index $= \sqrt{\frac{\varepsilon}{\varepsilon_{0}}} = 2$
$\therefore$ Speed and wavelength of wave becomes half and frequency remain unchanged
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.