A source emits a sound of frequency $400\text{ Hz}$, but the listener hears it to be $390\text{ Hz}$. Then,

A source emits a sound of frequency $400\text{ Hz}$, but the listener hears it to be $390\text{ Hz}$. Then,
  1. the listener is moving towards the source
  2. the source is moving towards the listener
  3. the listener is moving away from the source
  4. the listener has a defective ear

Solution

Since, apparent frequency is less than the actual frequency, hence the relative separation between source and listener should be increasing.

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