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 

• infrared waves produce heating in a microwave oven 

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.

• microwave infrared, ultraviolet, gamma rays

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 phase and perpendicular to each other

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

• 3 m^-1

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

• gamma -rays