According to Bohr's model, an electron in a hydrogen atom radiates energy when it

  • A. moves in a stable orbit
  • B. jumps from a higher energy level to a lower one
  • C. jumps from a lower energy level to a higher one
  • D. is at rest in the nucleus

Explanation

Bohr postulated that an electron in an allowed orbit does not radiate at all, contradicting classical electromagnetism, and that a photon is emitted only when it drops to a lower level, carrying exactly the energy difference. Absorbing a photon does the reverse and lifts the electron to a higher level. This is why emission and absorption spectra of an element show lines at the same wavelengths.

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