Important Questions of Electromagnetic Waves Physics | Zigya

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91.

An electromagnetic wave travels along Z- axis. The pair of space and time varying field is

  • Ey, Bx

  • By, Ez

  • Ex, By

  • Ez, Bx


92.

Arrange the following electromagnetic radiation in the order of decreasing energy.

A. Infrared waves         B. Ultraviolet rays

C. Orange light             D. Green light

  • B, C, A, D

  • D, A, C, B

  • B, D, C, A

  • A, C, D, B


93.

The electric field associated with an electromagnetic wave in vaccum is given by E = i 40 cos (kz − 6 x 108 t), where E, Z and t are in volt m-1, metre and second respectively. The value of wave vector (k) is

  • 2 m-1

  • 0.5 m-1

  • 6 m-1

  • 3 m-1


94.

Electrons with de-Broglie wavelength λ fall on the target in an X-ray tube. The cut-off wavelength of the emitted X-rays is

  • λ0 = 2mcλ2h

  • λ0 = 2hmc

  • λ0 = 2m2c2λ3h2

  • λ0 = λ


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95.

Which of the following electromagnetic waves have the smallest wavelength ?

  • γ-rays

  • X-rays

  • UV waves

  • infrared rays


96.

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


97.

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


98.

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


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99.

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


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