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.

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

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

If v_y , v_x and  v_m are the speeds of gamma rays, X-rays and microwaves respectively in vacuum,  then

• v_y > v_x >  v_m

• v_y < v_x < v_m

• v_y >  v_x >  v_m

• v_y = v_x = v_m

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

• $\frac{1}{\sqrt{{\mathrm{\mu }}_0 {\mathrm{\epsilon }}_0}}$

• $\sqrt{\frac{{\mathrm{\mu }}_0}{{\mathrm{\epsilon }}_0}}$

• $\sqrt{\frac{{\mathrm{\epsilon }}_0}{{\mathrm{\mu }}_0}}$

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

• lower

• higher

• same

• 0^°C

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

Which wavelength of sun is used finally as electric energy?

• Radio waves

• Infrared waves

• Visible light

• visible light

69.

CO₂ laser uses

• microwaves

• infra red

• ultra violet

• visible light

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