CBSE
Multiple Choice QuestionsThe 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
X-rays are
electromagnetic radiation
stream of electron
stream of proton
stream of uncharged particle
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
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
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 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
The velocity of electromagnetic radiation in a medium of permittivity 
and permeability 
is given by
Who discovered X-rays?
Roentgen
Madam Curie
Rutherford
All of these
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.
If represent the wavelengths of visible light, X-rays and microwaves respectively, then
