Under the Doppler Effect, an observer behind a moving wave source observes
increased wave frequency
no wave frequency
decreased wave frequency
unchanging wave frequency

Question

Under the Doppler Effect, an observer behind a moving wave source observes 
    increased wave frequency 
   no wave frequency 
   decreased wave frequency 
   unchanging wave frequency

anonymous · Answer

Decreased wave frequency. Think about a police car with its sirens driving away from you. Does it appear to be fading? Yes... that is decreased wave frequency.

anonymous · Answer

Deceased wave frequency. if the observer was in front of the source, the waves would get pushed together as it approached the observer. But if the observer is behind the source as the source goes away the wave frequency becomes more spaced out.