7: Exam Questions

Question 1

photons of red light are emitted by the neon atoms in the gas inside the laser. Explain what energy levels are and how they can be used to explain the emission of photons from atoms.

Answer 1

1) energy levels explanation: electrons have discrete energies in atom/AW
2) each photon produced by electron moving between levels
3) photon energy equal to energy difference between levels
4) electron loses energy/making transition in correct direction

Question 2

Another laser emits blue light. The power in its beam is also 1.0 mW. Explain why the laser emitting blue light emits fewer photons per second compared with a laser of the same power emitting red light.

Answer 2

1) blue light has a higher frequency/shorter wavelength than red light 2) energy per photon is higher (so fewer needed to produce one mW)