question_answer

A source of sound emits sound waves at frequency It is moving towards an observer with fixed speed  where  is the speed of sound in air). If the observer were to move towards the source with speed  one of the following two graphs (A and B) will give the correct variation of the frequency f heard by the observer as is changed.        [JEE MAIN 11-04-2015]

The variation of f with is given correctly by:

A)  graph A with slope

B)    graph A with slope

C)    graph B with slope

D)    graph B with slope

Correct Answer: A

Solution :

[a] For the given situation

frequency listened by an observer is f.

So,

equating the equation

So choice is [a].