JEE Main & Advanced Physics EM Waves JEE PYQ-Electro Magnetic Waves

  • question_answer
    An electromagnetic wave of frequency \[v=3.0MHz\]passes from vacuum into a dielectric medium with permittivity\[\varepsilon =4.0.\] Then,                                       [AIEEE 2004]

    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

    Correct Answer: C

    Solution :

    [c] For vacuum \[{{\varepsilon }_{0}}=1\]
    For medium \[\varepsilon =4\]
    So refractive index \[\mu =\sqrt{\varepsilon /{{\varepsilon }_{0}}}=\sqrt{4/1}=2\]
    Wavelength \[\lambda '=\frac{\lambda }{\mu }=\frac{\lambda }{2}\]
    and wave velocity \[v=\frac{c}{\mu }=\frac{c}{2}\]
    Hence it is clear that wavelength and velocity will become half but frequency remains unchanged when the wave is passing through any medium.


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