First slide

Introduction-Electromagnetic waves

Question

An electromagnetic wave of frequency f = 3.0 MHz passes from vacuum into a dielectric medium with relative permittivity $ε_{r} = 4.0$ and relative permeability $μ_{r} = 1.0$ Then

Moderate

A

Wavelength is halved and frequency remains unchanged
B

Wavelength is doubled and frequency becomes half
C

Wavelength is doubled and the frequency remains unchanged
D

Wavelength and frequency both remain unchanged

Solution

$F r e q u e n c y r e m a i n s c o n s \tan t d u r i n g r e f r a c t i o n v_{m e d} = \frac{1}{\sqrt{μ_{0} \in_{0} \times μ_{r} \in_{r}}} = \frac{1}{\sqrt{μ_{0} \in_{0} \times 4}} = \frac{c}{2} N o w, \frac{λ_{m e d}}{λ_{a i r}} = \frac{v_{m e d}}{v_{a i r}} = \frac{c / 2}{c} = \frac{1}{2} ∴ W a v e l e n g t h i s h a l v e d a n d f r e q u e n c y r e m a i n s u n c h a n g e d .$

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