Electromagnetic waves of frequencies higher than 92 MHz are

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 Multiple Choice QuestionsMultiple Choice Questions

11.

In a plane electromagnetic wave, the electric field of amplitude 1 Vm-1 varies with time in free space. The average energy density of magnetic field is (in Jm-2)

  • 8.86 × 10-12

  • 4.43 × 10-12

  • 17.72 × 10-12

  • 2.21 × 10-12


12.

Which one of the following is the property of a monochromatic, plane electromagnetic wave in free space?

  • Electric and magnetic fields have a phase difference of π2

  • The energy contribution of both electric and magnetic fields are equal.

  • The direction of propagation is in the direction of electric field E

  • The pressure exerted by the wave is the product of energy density and the speed of the wave


13.

If the magnetic field of an electromagnetic wave is given as By = 2 x 10-7 sin (103 x + 1.5x 1012 t) tesla, the wavelength of the electromagnetic wave is

  • 0.314 mm

  • 0.628 mm

  • 6.28 mm

  • 1.26 mm


14.

The electromagnetic waves travel with

  • the same speed in all media

  • the speed of sound in free space

  • the speed of light c = 3 x 108 ms-1 in free space

  • the speed of light c = 3 x 108 ms-1 in fluid medium


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15.

The speed of an electromagnetic wave in a material medium of permeability µ and permittivity is

  • 1με

  • 12με

  • 1με

  • 12με


16.

The energy of infrared waves is greater than that of

  • visible light

  • ultraviolet waves

  • micro waves

  • gamma rays


17.

Which one of the following is incorrect statement in the transmission of electromagnetic waves?

  • Ground wave propagation is for high frequency transmission.

  • Sky wave propagation is facilitated by ionospheric layers.

  • Space wave is of high frequency and is suitable for line of sight communication.

  • Space wave is used for satellite communication.


18.

The electric field of an electromagnetic wave travelling through vacuum is given by the equation E = Eo sin(kx − ωt). The quantity that is independent of wavelength is

  • kω

  • ω

  • k


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19.

The electric field of a plane electromagnetic wave varies with time of amplitude 2 Vm-1 propagating along z-axis. The average energy density of the magnetic field is (in Jm-3)

  • 13.29 × 10-12

  • 8.86 × 10-12

  • 17.72 × 10-12

  • 4.43 × 10-12


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20.

Electromagnetic waves of frequencies higher than 92 MHz are found to be reflected by the ionosphere on a particular day at a place. The maximum electron density in the ionosphere is

  • 5 × 1012 m-3

  • 2 × 1012 m-3

  • 2 × 1012 m-3

  • 5 × 1012 m-3


C.

2 × 1012 m-3

The frequency of electromagnetic waves

    v = 9maximum electron densityor v = 9dmaxor 92 × 106 = 9dmaxor    2 × 106 = dmaxor              dmax = 2 × 1012 m-3


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