The electric and magnetic field of an electromagnetic wave are:

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 Multiple Choice QuestionsMultiple Choice Questions

41.

If E and B represent electric and magnetic field vectors of an electromagentic wave, the direction of propagation of the wave is along

  • E × B

  • B × E

  • E

  • B


42.

Out of the following statements which is not true ?

  • Infrared radiations arise due to minor electron transitions in atoms

  • Infrared radiations are used for long distance photography

  • Sun is the natural source of infrared radiation

  • Infrared radiations are detected by using a bolometer


43.

The electric field associated with an electromagnetic wave in vacuum is given by E=i 40 cos (kz-6x108t), where E, z= and t are in volt/m, metre and second respectively. The value of wave vector k is

  • 2 m-1

  • 0.5 m-1

  • 6 m-1

  • 6 m-1

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44.

The condition under which a microwave oven heats up a food item containing water molecules most efficiently is

  • the frequency of the microwave must match the resonant frequency of the water molecules

  • the frequency of the microwave has no relation  with natural frequency of water molecules

  • microwave are heat waves, so always produce heating 

  • microwave are heat waves, so always produce heating 

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45.

The decreasing order of wavelength of infrared, microwave, ultraviolet and gamma rays is

  • gamma rays, ultraviolet, infrared, microwaves

  • microwaves, gamma rays, infrared, ultraviolet

  • infrared, microwave, ultraviolet, gamma rays.

  • infrared, microwave, ultraviolet, gamma rays.

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46.

The energy of the EM waves is of the order of 15 keV. To which part of the spectrum does it belong?

  • X - rays

  • infrared rays

  • Ultraviolet rays

  • Ultraviolet rays

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47.

The velocity of electromagnetic radiation in a medium of permittivity straight epsilon subscript straight o and permeability straight mu subscript straight o is given by

  • square root of epsilon subscript o over mu subscript o end root
  • square root of straight mu subscript straight o straight epsilon subscript straight o end root
  • fraction numerator 1 over denominator square root of straight mu subscript straight o straight epsilon subscript straight o end root end fraction
  • fraction numerator 1 over denominator square root of straight mu subscript straight o straight epsilon subscript straight o end root end fraction
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48.

The electric and magnetic field of an electromagnetic wave are:

  • in phase and parallel to each other

  • in opposite phase and perpendicular to each other

  • in opposite phase and parallel to each other

  • in opposite phase and parallel to each other


D.

in opposite phase and parallel to each other

Electromagnetic waves are those waves in which there are a sinusoidal variation of electric and magnetic field vectors at right angles to each other as well as right angles to the direction of wave propagation.
The sinusoidal variation in both electric and magnetic field vectors ( occurs, simultaneously. As a result, they attain the maxima and minima at the same place and at the same time. The amplitudes of the electric and magnetic fields in free spaces are related by



In the figure, electric field vector and magnetic field vector () are vibrating along Y and Z directions and propagation of the electromagnetic wave is shown in X -direction.

Hence, electric and magnetic fields are in phase and perpendicular to each other.

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49.

X-rays are

  • electromagnetic radiation

  • stream of electron

  • stream of proton

  • stream of uncharged particle


50.

Who discovered X-rays?

  • Roentgen

  • Madam Curie

  • Rutherford

  •  All of these


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