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

What physical change occurs when source of sound moves and observer is stationary?

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

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

What is the physical change occurs when the source of sound is stationary but the observer moves?

At what velocity should a source of sound move towards a listener so that apparent frequency is twice the actual frequency?

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.

State the expression for apparent frequency when source of sound and listener are moving towards each other