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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.

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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 : 2

  • 1 : 8

  • 4 : 1

  • 1 : 4


D.

1 : 4

Given, ZA : ZB = 1 : 2

We know,  v ∝ Z2

Hence, vAvB = 1222

     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).


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