If vy , vx and  vm are the speeds of gamma rays, X-rays and

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 Multiple Choice QuestionsMultiple Choice Questions

61.

Assertion:  Electromagnetic waves are transverse in nature 

Reason: The electric and magnetic fields of an e.m. wave are perpendicular to each other and also perpendicular to the direction of wave propogation.

  • 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.


62.

Assertion:  X-ray astronomy is possible only from satellites orbiting the earth. 

Reason:  Efficiency of X-rays telescope is large as compared to any other telescope.

  • 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


63.

Black  holes  in  orbit  around  a  normal  star  are  detected  from  earth  due  to  the  frictional  heating  of  infalling  gas  into  the  black  hole,  which  can  reach  temperatures  greater  than  106 K.  Assuming  that  the  infalling  gas  can  be  modelled  as  a  blackbody  radiator,  then  the  wavelength  of  maximum  power  lies

  • in the visible region

  • in the X-ray region

  • in the microwave region

  • in the gamma-ray region of electromagnetic spectrum


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64.

If vy , vx and  vm are the speeds of gamma rays, X-rays and microwaves respectively in vacuum,  then

  • vy > vx >  vm

  • vy < vx < vm

  • vy >  vx >  vm

  • vy = vx = vm


D.

vy = vx = vm

Increasing the order of frequencies of the spectrum is given by

  Radio waves < micro-wave < visible rays < ultraviolet rays < X-rays < gamma rays < cosmic rays

And

The order of the wavelength of spectrum is given by

Radio waves  > micro wave >  infrared wave >  visible rays >  ultraviolet rays > x-rays >  gamma rays >  cosmic rays

but

speed of each radiation equals 3 × 108 m/s

 Because all the radiations are component of electromagnetic waves and speed of the electromagnetic wave is 3 ×  108 m/s

Hence 

 Vg = Vx  = Vm = 3 ×  108 m/s


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65.

The velocity of electromagnetic radiation in a medium of permittivity ε0 and permeability μ0 is given by 

  • 1μ0 ε0

  • μ0ε0

  • ε0μ0


66.

If there were no atmosphere, the average temperature on earth surface would be

  • lower

  • higher

  • same

  • 0°C


67.

Assertion:  X-rays can penetrate through the flesh but not through the bones. 

Reason:  The penetrating power of X-rays depends on voltage.

  • 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


68.

Which wavelength of sun is used finally as electric energy?

  • Radio waves

  • Infrared waves

  • Visible light

  • visible light


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69.

CO2 laser uses

  • microwaves

  • infra red

  • ultra violet

  • visible light


70.

Assertion: Dipole oscillations produce electromagnetic waves.

Reason: Accelerated charge produces electromagnetic waves.

  • 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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