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 1015 –1017Hz.
Two elements A and B with atomic numbers ZA and ZB are used to produce characteristic X-rays with frequencies vA and vB respectively. If ZA : ZB = 1 : 2, then vA : vB will be
1 : 8
4 : 1
1 : 4
D.
1 : 4
Given, ZA : ZB = 1 : 2
We know, v ∝ Z2
Hence,
vA : vB = 1 : 4
In which of the following phenomena, the heat waves travel along straight lines with the speed of light ?
Thermal conduction
Forced convection
Natural convection
Thermal radiation
D.
Thermal radiation
Thermal radiation is the heat waves travel along straight lines with the speed of light.
The energy of gamma (γ) ray photon is Eγ and that of an X-ray photon is Ex. If the visible light photon has an energy of Ev, then we can say that
EX > Eγ > Ev
Eγ > Ev > EX
Eγ > EX > Ev
EX > Ev > Eγ
C.
Eγ > EX > Ev
Eγ ≥ 100 keV
EX = 100 eV to 100 keV
Ev = 2.48 eV
So, we can say that
Eγ > EX > Ev
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 electromagnetive wave, therefore the correct choice is (a).