Discussion Forum

1)

 An  electromagnetic wave of frequency 3.0 MHz passes from vacuum into a  non-magnetic medium with permittivity,  

$\epsilon=16 \epsilon_{0}$ . where $\epsilon_{0}$ is the free space permittivity. The change in wavelength is 

Answer:

Option A

Explanation:

Given , frequency of EM wave 

f=3MHz

= $3 \times 10^{6}$ Hz

 and permittivity of non -magnetic medium

 $\epsilon=16\epsilon_{0}$

 Wave length of EM wave,

 $\lambda=\frac{c}{f}=\frac{3 \times 10^{8}}{3 \times 10^{6}}$

$\lambda$  =100 m

Velocity of electromagnetic (EM)  into non-magnetic  material

   $v=\frac{c}{\sqrt{\epsilon_{r}}}=\frac{3 \times 10^{8}}{\sqrt{16}}$     $\left[ \because \epsilon_{r}=\frac{\epsilon}{\epsilon_{0}}=16\right]$

    = $\frac{3}{4}  \times 10^{8}$  m/s

 $\therefore$    Wavelength  ,   $\lambda'=\frac{v}{f}=\frac{\frac{3}{4}\times 10^{8}}{3 \times 10^{6}}=25 m$

$\therefore$   Change in wave length = $\lambda'- \lambda$

  =25-100= -75 m