CBSE
Gujarat Board
Haryana Board
Class 10
Class 12
Welders wear special goggles or face masks with glass windows to protect their eyes from electromagnetic radiations. Name the radiations and write the range of their frequency.
The radiations are ultraviolet radiations.
The frequency range of UV rays is 10^{15} –10^{17}Hz.
During the propagation of electromagnetic waves in a medium:
Electric energy density is equal to the magnetic energy density.
Both electric and magnetic energy densities are zero.
Electric energy density is double of the magnetic energy density.
Electric energy density is half of the magnetic energy density.
C.
Electric energy density is double of the magnetic energy density.
An electromagnetic wave in vaccum has the electric and magnetic fields and which are always perpendicular to each other. the direction of polarisation is given by and that of wave propagation by then
C.
The threshold frequency for a metallic surface corresponds to an energy of 6.2 eV, and the stopping potential for a radiation incident on this surface 5 V. The incident radiation lies in
X-ray region
ultra-violet region
infra-red region
visible region
B.
ultra-violet region
The electric field associated with an electromagnetic wave in vacuum is given by E=i 40 cos (kz-6x10^{8}t), 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}
A.
2 m^{-1}
Electromagnetic wave equation
Electromagnetic wave equation
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
A.
the frequency of the microwave must match the resonant frequency of the water molecules
It is an electromagnetic wave, therefore the correct choice is (a).
It is an electromagnetic wave, therefore the correct choice is (a).