Question

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

• A. wavelength is doubled and 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

Answer 1

Answer: (C)

wavelength is halved and frequency remains unchanged

$f=3.0mHz$

$E=4.0$

$C=fZ$

C is the speed of light into the medium

$C_0=f_i{Z}_{i}C=\frac{C_0}{n}C=f_f{Z}_{f}n=\sqrt{\frac{\epsilon }{{\epsilon }_0}}C=\frac{C_0}{2}$

Now since frequency depends on source

Hence $f_f=f_i{Z}_f=\frac{Z_i}{2}$

Speed and wavelength will be halved