Question

Identify the statements with no Doppler effect:
a) Source of sound and listener both are at rest but a strong wind is blowing
b) A whistle is being revolved in a horizontal circle with the observer standing outside the circle.
c) Source of sound and observer are moving relatively perpendicular to one another.

• A. only a
  
• B. both a and b
• C. only c
• D. a, b, c

Answer 1

The correct option is C only c

a) the statement may be a case of doppler effect as both source and observer are at rest but wind is blowing , so when we take relative velocity of source and observer with respect to wind in the direction of propogation of sound , the situation becomes as source and observer both are moving in same direction with same speed .

b) this option is a case of doppler effect as the object will have varying velocity in the direction of instantaneous line joining the source and observer while the source (whistle) will complete the circle.

c) since source and observer are not having any relative velocity in the direction of line joining them so this is not a case of doppler.

so the answer is c.