1.

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

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 

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.

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

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

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

X-rays are

• electromagnetic radiation

• stream of electron

• stream of proton

• stream of uncharged particle

Who discovered X-rays?

• Roentgen

• Madam Curie

• Rutherford

•  All of these

If  ${\mathrm{\lambda }}_{\mathrm{\nu }}, {\mathrm{\lambda }}_{\mathrm{x}} \mathrm{and} {\mathrm{\lambda }}_{\mathrm{m}}$represent the wavelengths of visible light, X-rays and microwaves respectively, then

• ${\mathrm{\lambda }}_{ \mathrm{m}} > {\mathrm{\lambda }}_{ \mathrm{x}} > {\mathrm{\lambda }}_{ \mathrm{\nu }}$

• ${\mathrm{\lambda }}_{\mathrm{v}} >{\mathrm{\lambda }}_{\mathrm{m}} > {\mathrm{\lambda }}_{\mathrm{x}}$

• ${\mathrm{\lambda }}_{\mathrm{m}}> {\mathrm{\lambda }}_{\mathrm{v}} > {\mathrm{\lambda }}_{\mathrm{x}}$

• ${\mathrm{\lambda }}_{\mathrm{v}} > {\mathrm{\lambda }}_{\mathrm{x}} > {\mathrm{\lambda }}_{\mathrm{m}}$

In gamma ray emission from a nucleus

• both the neutron number and the proton number change

• there is no change in the proton number and the neutron number

• only the neutron number changes

• only the proton number changes