In short wave communication, waves of which of the following

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 Multiple Choice QuestionsMultiple Choice Questions

71.

Asserion: : NAND is a universal gate.

Reason: It can be used to describe all other logic gates.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false


72.

Assertion: Magnetic Resonance Imaging (MRI) is a useful diagnostic tool for producing images of various parts of human body. 

Reason:  Protons of various tissues of human body play a role in MRI.

  • If both assertion and reason are true and reason is the correct explanation of the assertion

  • If both assertion and reason are true but reason is not the correct explanation of the assertion

  • If assertion is true, but reason is false

  • Both assertion and reason are false statements


73.

In case of linearly polarised light, the magnitude of the electric field vector

  • does not change with time

  • varies periodically with time

  • increases and decreases linearly with time

  • is parallel to the direction of propagation


74.

Assertion:  The true geographic north direction is found by using a compass needle.

Reason: The impurities meridian of the earth is along the axis of rotation of the earth.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false


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75.

Assertion: There are very small sporadic changes in the period of rotation of the earth. 

Reason: Shi fling of large air masses in the earth's atmosphere produce a change in the moment of inertia of the earth causing its period of rotation to change.

  • If both assertion and reason are true and reason is the correct explanation of assertion

  • If both assertion and reason are true but reason is not the correct explanation of assertion

  • If assertion is true but reason is false

  • If both assertion and reason are false


76.

The maximum distance upto which TV transmission from a TV of height h can be received is proportional to

  • h1/2

  • h

  • h3

  • h2


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77.

In short wave communication, waves of which of the following frequencies will be reflected back by the ionospheric layer having electron density 1011 per  m3 ?

  • 2 MHz

  • 10 MHz

  • 12 MHz

  • 18 MHz


A.

2 MHz

The layer of the earth's atmosphere which contains high concentration of ions and free electrons and is able to reflect radio waves. It lies above the mesosphere.

We know that the artificial frequency of a sky wave for reflection from an ionospheric layer of the atmosphere is given by    

  νc = 9 N1/2

where  n is the number density of electrons /m3

It  is given that

    N = 1011 m3   

  νc = 9 ×  ( 1011 )1/2

       = 2.8 × 106 Hz   

  νc = 2.8 MHz

Hence the wave of frequency 2 MHz will be reflected back.


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78.

X-ray beam are affected by

  • electric field

  • magnetic field

  • both (a) and (b)

  • none of these


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79.

All components of the electromagnetic spectrum in vacuum have the same

  • energy

  • velocity

  • wavelength

  • frequency


80.

The difference between soft and hard X-rays is of :

  • velocity

  • intensity

  • frequency

  • polarization


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