Question

Two sound sources shown in the figure vibrate in phase. By - L₂ has values, 20 cm, 60 cm and 100 cm. If the frequency of sound source is 1700/n Hz. Then find the value of n : [Speed of sound is 340 m/s]

Answer 1

The minima will be heard at P when a crest from S₁ and a trough from S₂ reach there at the same time. This will happen if L₁ - L₂ is λ/2 or λ + (λ/2) or 2λ + (λ/2) and so on. Hence, the increase in L₁ between consecutive minima is λ₁ and from the data we see that λ = 0.40 m. Then from λ = v/f  

⇒ f = 340/0.40 = 850 Hz