Electromagnetic theory miscellaneous


Electromagnetic theory miscellaneous

Electromagnetic Theory

  1. An uniform plane wave incident normally on a plane surface of dielectric material is reflected with a VSWR of 3 what is the percentage of incident power that is reflected?









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    Percentage of reflected power given by
    P– R = | Γ |2 Pi+

    Γ =
    3 – 1
    2
    =
    1
    3 + 142

    PR– =
    1
    2 Pi+
    2

    so percentage reflected power
    PR
    × 100 =
    1
    × 100 = 25%
    Pi4

    Correct Option: B

    Percentage of reflected power given by
    P– R = | Γ |2 Pi+

    Γ =
    3 – 1
    2
    =
    1
    3 + 142

    PR– =
    1
    2 Pi+
    2

    so percentage reflected power
    PR
    × 100 =
    1
    × 100 = 25%
    Pi4


  1. A material has conductivity of 10–2 mho/m and a relative permittivity of 4 the frequency at which conduction current in the medium is equal to the displacement current is—









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    As hints are provided in the synopsis that displacement current is the rate of change of electric flux density, so we get

    JC = σ E, JD =
    ∂D
    ⇒ ωD = ω ε0εr E
    ∂t

    so when both currents are equal
    JC = JD ⇒ σE = ω ε0 εr E
    ω =
    σ
    ε0 εr

    f =
    σ
    2π × 8.85 × 10–12 × 4

    = 4.49 × 1010–3 × 1010 = 45 MHz

    Correct Option: A

    As hints are provided in the synopsis that displacement current is the rate of change of electric flux density, so we get

    JC = σ E, JD =
    ∂D
    ⇒ ωD = ω ε0εr E
    ∂t

    so when both currents are equal
    JC = JD ⇒ σE = ω ε0 εr E
    ω =
    σ
    ε0 εr

    f =
    σ
    2π × 8.85 × 10–12 × 4

    = 4.49 × 1010–3 × 1010 = 45 MHz



  1. The dominant mode in a rectangular waveguide is TE10 because this mode has—









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    For the dominant mode either cut-off frequency should be lowest or cut-off wavelength should be highest.

    Correct Option: D

    For the dominant mode either cut-off frequency should be lowest or cut-off wavelength should be highest.


  1. The phase velocity of wave propagating in a hollow metal waveguide is—









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    Explained in the synopsis provided.

    Correct Option: A

    Explained in the synopsis provided.



  1. If a plane electromagnetic wave satisfies the equation
    2Ex
    = e2
    2Ex
    ∂z2∂t2

    the wave propagates in—









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    For the propagation of plane electromagnetic wave their is change in the intensity (magnitude) of wave in the direction of propagation with the time.

    Correct Option: B

    For the propagation of plane electromagnetic wave their is change in the intensity (magnitude) of wave in the direction of propagation with the time.