18 SECTION B Answer ALL questions. 16 Read the passage and answer the questions that follow. Atoms can be promoted into an excited state when they absorb energy. This results in the release of radiation at a random time. When several atoms are close together a quantum effect can occur. When one atom emits radiation this affects all the other nearby excited atoms. The excess energy of many of the atoms is released simultaneously and an intense flash of light is produced. This effect is called superradiance and can be used to produce lasers that emit a narrower range of frequencies than conventional lasers. (a) When superradiance occurs the atoms all absorb the same amount of energy. Explain how this results in all the atoms emitting radiation of a particular frequency. 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An atom is in the ground state. The atom absorbs 6.2 eV of energy. The distance between neighbouring atoms is 140 nm. Deduce whether superradiance can occur. 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(c) Superradiant lasers are highly monochromatic. Explain why a monochromatic light source is important in diffraction experiments. 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(Total for Question 16 = 11 marks)