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Which of the following is an electromagnetic wave ?

  • A.Sound wave
  • B.Cathode rays
  • C.Infra red rays
  • D.Ultrasonic wave

Answer: C

Infrared rays are electromagnetic.

They are oscillating electric and magnetic fields and travel through vacuum at \(3\times10^{8}\ \mathrm{m\,s^{-1}}\). Sound and ultrasonic waves are mechanical and need a medium; cathode rays are a stream of electrons, which are particles.

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