What physical change occurs when source of sound waves is at rest and the listener moves?

What physical change occurs when a source of sound moves and listener is at rest?

A source of sound moves towards an observe.

Assertion : The apparent frequency will remain same as the frequency of source of sound if source and listener move at right angles to each other. Reason : Apparent frequency will always increase whether source is moving towards the listener or listener is moving towards the source.

A source of sound moves towards a listener with a velocity equal to that of sound. If the source emits n waves per second, then the listener moving away from the source with the same velocity receives

A listener is at rest with respect to the source of sound. A wind starts blowing along the line joining the source and the observer which of the following quantities don't change ?