A physicist is in court, defending herself on the charge of running a red light. She testifies that because of the Doppler effect, as she approached the intersection, the light appeared green to her. Which of the following best describes the Doppler effect?
1) The change in frequency or wavelength of a wave as observed by an observer moving relative to the source of the wave
2) The change in frequency or wavelength of a wave as observed by an observer standing still relative to the source of the wave
3) The change in amplitude of a wave as observed by an observer moving relative to the source of the wave
4) The change in amplitude of a wave as observed by an observer standing still relative to the source of the wave