Question

An electromagnetic wave of frequency $v=3.0MHz$ passes from vacuum into a dielectric medium with permittivity $ϵ=4.0$. Then

• A. wavelength is halved and frequency remains unchanged.
• B. wavelength is doubled and frequency becomes half.
• C. wavelength is doubled and frequency remains unchanged.
• D. wavelength and frequency both remain unchanged.

Answer 1

The correct option is A wavelength is halved and frequency remains unchanged.

Frequency remains constant during refraction.
$v_{med}=\frac{1}{\sqrt{{\mu }_0{ϵ}_0\times 4}}=\frac{c}{2}$
$\frac{{\lambda }_{med}}{{\lambda }_{air}}=\frac{v_{med}}{v_{air}}=\frac{\frac{c}{2}}{c}=\frac{1}{2}$
$\therefore$ wavelength is halved and frequency remains unchanged.