Question

There are three sources of sound of equal intensities and frequencies 400,401 and 402 vibrations per second.The number of beats/sec is

• A. 0
• B. 1
• C. 3
• D. 2

Answer 1

Answer: (B)

1

Beating is the periodic variation of intensity at a given point due to superposition of two waves having slightly different frequencies. The number of intensity maxima one hears per second, or the beat frequency, equals the difference in frequency between the two sources.

Thus here the beat frequency $=401-400=402-401=1$